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Thesis Supervisor: Hans-Georg Wallentinus           Department of Landscape Planning,
Thesis for the Degree of Master in Biology          Ultuna, EIA centre
20 credit points, 2002                              SLU
                                                  7$%/( 2) &217(17


   1.1 BACKGROUND ................................................................................................................... 6
   1.2 AIM ................................................................................................................................... 7
   1.2 METHOD ........................................................................................................................... 7
   1.3 SCOPE ............................................................................................................................... 8
   2.1 THE MALARIA PARASITE.................................................................................................... 8
   2.2 MALARIA VECTORS OF MALARIA....................................................................................... 9
   2.3. CLINICAL SYMPTOMS ..................................................................................................... 10
 &855(17 0$/$5,$ 6,78$7,21  

 0$/$5,$ &21752/ 0(7+2'6  
   4.1 REDUCTION AND CONTROL OF ADULT VECTORS .............................................................. 13
       &+(0,&$/ &21752/   DDT ................................................................................................................. 14 SYNTHETIC PYRETHROIDS ................................................................................. 15 INSECTICIDE TREATED BEDNETS ........................................................................ 16
       %,2/2*,&$/ &21752/   NATURAL PLANT EXTRACT................................................................................ 19
   4.2 CONTROL OF MOSQUITO LARVAE .................................................................................... 20
       %,2/2*,&$/ &21752/   BTI .................................................................................................................... 21 LARVIVOROUS FISH ........................................................................................... 22 HABITAT MANAGEMENT.................................................................................... 23
   4.3 GENETIC CONTROL .......................................................................................................... 24
 (&2/2*,&$/ ,03$&7  
   5.1 REDUCTION AND CONTROL OF ADULT VECTORS .............................................................. 25
       &+(0,&$/ &21752/   DDT ................................................................................................................. 25 SYNTETHIC PYRETHROIDS ................................................................................. 27 INSECTICIDE TREATED BEDNETS ........................................................................ 28
       %,2/2*,&$/ &21752/   PLANT EXTRACT ............................................................................................... 29
   5.2 CONTROL OF MOSQUITO LARVAE .................................................................................... 29
       %,2/2*,&$/ &21752/   BTI .................................................................................................................... 29 LARVIVOROUS FISH ........................................................................................... 30 HABITAT MANAGEMENT.................................................................................... 30
   5.3 GENETIC CONTROL .......................................................................................................... 31
 ,03$&7 21 +80$1 +($/7+ 
   6.1 REDUCTION AND CONTROL OF ADULT VECTORS .............................................................. 31

       &KHPLFDO FRQWURO  DDT ................................................................................................................. 31 SYNTETHIC PYRETHROID ................................................................................... 32 INSECTICIDE TREATED BEDNETS ........................................................................ 33
       %,2/2*,&$/ &21752/   PLANT EXTRACT ................................................................................................ 35
   6.2 CONTROL OF MOSQUITO LARVAE .................................................................................... 35
       %,2/2*,&$/ &21752/   BTI .................................................................................................................... 35 LARVIVOROUS FISH ........................................................................................... 35 HABITAT MANAGEMENT.................................................................................... 36
   6.3 GENETIC CONTROL .......................................................................................................... 36
   7.1 REDUCTION AND CONTROL OF ADULT VECTORS .............................................................. 37
       &+(0,&$/ &21752/   DDT ................................................................................................................. 37 SYNTHETIC PYRETHROID .................................................................................. 37 INSECTICIDE TREATED BEDNETS ........................................................................ 38
       %,2/2*,&$/ &21752/   NATURAL PLANT EXTRACT................................................................................ 39
   7.2 CONTROL OF MOSQUITO LARVAE .................................................................................... 39
       %,2/2*,&$/ &21752/   BTI .................................................................................................................... 39 LARVIVOROUS FISH ........................................................................................... 40 HABITAT MANAGEMENT.................................................................................... 40
   7.3 GENETIC CONTROL .......................................................................................................... 40



This thesis examines different ways of controlling malaria, which is one of the most harmful
parasitic diseases in the world. In addition, these control methods are analysed concerning
their impact on the ecological surrounding and to human health. The economical aspects of
each method are also discussed.

More than one million people die yearly of malaria and about 300-500 million people acquire
attack of acute illness every year, why an effective control of the disease is needed. Malaria is
mainly controlled by a reduction of the vectors of malaria, i.e. mosquitoes. They may be
controlled either as adult mosquitoes or as larvae. The control methods of adult mosquitoes
discussed in this thesis are indoors spraying with insecticide (DDT and pyrethroids),
chemically treated bednets and a use of repellent plant extract. Indoors spraying is effective
and comparatively inexpensive, especially when using DDT, which also has been the most
important chemical in the history of controlling malaria. However, the use of chemicals
always involves environmental risks. DDT and pyrethroids are mainly harmful for aquatic
organisms or for animals dependent on aquatic organisms, why these environments should be
protected. The effect on human health due to the use of insecticides is mainly from handling
the chemical, i.e. the treatment process. Insecticide treated bednets has proven to be very
effective agasint malaria, as it give rise to a physical protection against the mosquitoes as well
as a chemical. The nets are environmental favourable but the impregnation of the nets may
involve a risk for contamination of water environment, if the wastes are not taken care of
properly. The use of natural plant does not give rise to any known impact on the environment
or on human health. However, the efficiency towards malaria is not really studied.

Mosquitoes can also be killed as larvae. An introduction of mosquito pathogens or predators
to mosquito-breeding sites can be effective if all sites in the affected area are found. Bacteria
or larval eating fish are examples vector pathogens and predators that are brought up in this
thesis. The bacteria, %DFLOOXV WKXULQJLHQVLV LVUDHOHQVLV (Bti) have been the most promising
larval method for controlling malaria so far. However, the compound may in rare cases affect
other organisms than the target vectors and the method is expensive to use. Another larvae
control method is vector habitat management, which involves permanently or temporarily
elimination of wetlands and water bodies that is being favoured as mosquito breeding sites.
This method was used for eradication of malaria in many western countries in the 1950th and

in the 1960s. But as wetlands are crucial habitats for many organisms, this management is
often done at the expense of many important organisms.

Finally, there is also possible to control mosquitoes by genetic methods. Traditionally this
involves a release of sterile male mosquito into the target mosquito population. The sterile
males mate with the females and hence do not leave any offspring. Recently, American
scientist has discovered a way to make the mosquitoes immune against the parasites that
transmit the disease, which is a promising discovery for the future. However, a genetic control
is always very expensive and maybe not an alternative in developing countries.



Malaria is by far the most predominant tropical parasitic disease. It exists in more than 100
countries, which are inhabited by a total of some 2 400 million people. The parasite causes
300-500 million attack of acute illness globally every year, of which more than 1 million
people die. The vast majority of these deaths occur among young children in Africa. (WHO,

Malaria and the mosquitoes that transmit the disease have since the 1940s effectively been
controlled with organic pollutants such as DDT (dichlorodiphenyltrichloroethane). However,
DDT belongs to a group of chemicals called persistent organic pollutants (POPs), which all
are known to be extremely harmful when being dispersed in nature. (Bernes, 1998) In May
2001, more than hundred diplomats signed a treaty on facing out the use of POPs. If the
necessary 50 ratifications are deposited by September 2002, the convention can come into
force before the end of 2002. (WWF, 2001) Malaria control with DDT then needs to be
replaced by other methods.

Malaria and underdevelopment are closely intertwined. Over 40% of the world’s population
are at risk of malaria. (WHO, 1999c) The Swedish authority for international aid, Sida’s
(Swedish international development co-operation agency) overall objectives are to raise the
standard of living for poor people. (Sida, 2001) However, this cannot be done at the expense
of the environment, why Sida are hesitant when it comes to allowing aid for malaria control
with DDT. However there are many other chemicals as well as methods available. The use of
biological substances, a more widespread use of impregnated bednets and modification of
vector breeding sites, are some examples. Nevertheless, different methods have different
effects as well as different consequences on human health and the ecological surroundings. It
is therefore of great concern for Sida and similar organisations to be familiar with the
advantages and disadvantages of the different malaria methods when handling a request of

The overall objectives of this thesis, is to study different malaria control methods and examine
their ecological impact as well as their effects on human health and economics.

This thesis is written at the request of Sida’s Environmental Policy Division. The study is
based on literature but some information has also been received through personal
communication. The thesis is made as a class screening project report1 for malaria control,
were the advantages and disadvantages for each control method are displayed, concerning
efficiency, ecological effect, human health and cost.

Not many class-screening reports have been made in Sweden and no established model for
how to make them have been set up. However, it is a general opinion that models of this kind
are important for simplifying the work with environmental impact assessments (EIAs), as they
would save time and resources, while working with the screening process. If the screening is
conducted in an effective way, more effort could be concentrated on important site specific
effects and mitigation, which would improve the effectiveness of the EIA process.

Sources of literature have been the library at the Department of Women’s and Children’s
Health at the Uppsala University, section of International Maternal and Child Health (IMCH),
which have provided all the necessary literature published by the World Health Organisation,
WHO. Thomas Jaenson at Uppsala University, Department of Evolutionary Biology,
Department of systematic zoology has given me a lot of material and articles, especially
concerning the use of DDT and impregnated bednets. Other sources are articles found at the
Swedish University of Agricultural Science in Uppsala, the Karolinska Institute’s library in
Solna, the library of the National Institute for Working Life, Stockholm and the Internet.

  A class screening report is a model for environmental impact assessment (EIA) within a group of projects with
similar or common characteristics in term of type, time frames and environmental effects.

The aim of this report is, as mentioned earlier, to present different control methods and to
evaluate different effects that arise due to those malaria control method. The effects looked
upon here are the ecological, social (human health) and economical effects. These are chosen
as the term sustainability is based on these three keystones. However, all available malaria
methods are not dealt with in the report; the emphases are instead on choosing the most
common or most effective methods and describe these thoroughly. For example there are
numerous chemicals that can be used when controlling mosquitoes in insecticide house
spraying programmes, yet only DDT and two pyrethroids are dealt with here. They are
chosen, as they are effective as well as economically feasible in developing countries.

Malaria is a treatable disease and can be controlled with drugs and prophylactics. However,
these treatments are expensive and resistance prevalent, they are therefore not considered in
this report apart from a brief description in chapter 8.

As this paper is a class screening report it does not concern a specific location that need to be
controlled, but analyses effects and consequences of the malaria control method in general.


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Human malaria is caused by a single celled protozoan parasite, belonging to the genus
3ODVPRGLXP. The parasites are dependent on $QRSKHOHV mosquitoes and human hosts for
completing its lifecycle, which consists of two phases; a sexual phase in female $QRSKHOHV
mosquitoes, and an asexual phase in man. The four recognised malaria parasites are 3 YLYD[
3 RYDOH 3 PDODULDH and 3 IDOFLSDUXP of which 3IDOFLSDUXP is the most pathogenic of the
four species. (WHO, 1997) Malaria is principally a tropical disease as the parasites are
unlikely to complete their cycle and hence to further propagate the disease, if temperature
drops below 15-19°C. (Martin, 1995)

The life cycle of a 3ODVPRGLXP parasite starts with a bite from an infected $QRSKHOHV, when it,
with its saliva, transfers hundreds to thousands 3ODVPRGLXP sporozoites into the human host.
The parasites enter the host’s bloodstream and reach the liver, where it multiplies asexually.
Subsequently, they return into the bloodstream and pursue their development in the red blood
cells. It is now the victim (the infected human) starts to feel ill The parasites then alter
between male and female forms and hence enter the sexual phase. When another mosquito
bites the infected human, it picks up both male and female forms which, finally mate in the
digestive track of the insect. The new generation of malaria parasites moves to the salivary
glands in the mosquito, waiting to start another cycle.
(Gilles et al., 1993, WHO, 1997, Martin, 1995)

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As mentioned above, only $QRSKHOHV mosquitoes, which belong to the order 'LSWHUD can
transmit human malaria Altogether there are approximately 380 species of $QRSKHOHV, of
which only some 60 are vectors of malaria. The $QRSKHOHV vectors are most frequent in
tropical and subtropical region, but can also be found in tempered climates and even in the
Arctic during the summer. They are though not found at altitudes above 2000-2500. Gilles et
al., 1993

It is only the female $QRSKHOHV mosquitoes that blood feed; they need the protein from the
blood meal to produce eggs. $QRSKHOHV mosquitoes are principally active between sunset and
sunrise, each species with their own specific peak-biting hour. Many $QRSKHOHV bite both
animals and humans but they often prefer one to the other. The ones that prefer humans are of
course more dangerous as vectors of human malaria. (WHO, 1997)

The successive stage of growth for an $QRSKHOHV mosquito is egg, larvae, pupa and finally
adult. Eggs are laid directly on the surface of a water body. Unlike other mosquitoes they are
provided with air-filled floats that allow them to remain on the water surface. Within 2-3 days
the eggs hatch and larvae develops. Another specific characteristic of the $QRSKHOHV are that
the larvae float parallel to the water surface instead of resting at an angle to the water surface
(fig 1.) The larvae swim by sweeping movements of the body and feed on yeast, bacteria and
small aquatic organisms. The fully-grown larva then alters into a pupa, which does not feed.

Finally, 7-18 days after the eggs are laid the pupa skin splits and an adult mosquito emerge.
(Gilles et al., 1993, WHO, 1997)

                  Fig. 1. Some of the main characteristics for differentiating $QRSKHOHV Notice
             the difference between $QRSKHOHV and their close relatives, $HGHV and &XOH[ mosquitos

Larval habitats vary from species to species. Preferred spots are still areas in slow-running
streams, stagnate pools of water and rice fields. The larvae prefer to be exposed to sunlight
but it also needs grass or mats of floating vegetation or algae for cover on the water body.
(WHO, 1997, Agyepong et al., 1995) The closer humans are to $QRSKHOHV breeding sites, the
higher contact between them and the vector, and the greater the risk of infection and
transmission. (Agyepong et al., 1995)

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Typical symptoms of malaria are influenza-like cyclic attacks of fevers. The attacks of fever
coincide with the waves of parasite multiplication and destruction of red blood cells. The
symptoms vary between different parasite species but common signs include chills, headache

and muscle pains. If the infection is long lasting, anaemia and enlargement of the liver can
occur. 3IDOFLSDUXP give rise to the most severe type of malaria. If the illness is untreated it
may lead to shock, kidney and liver failure, coma or death. This parasite can also cause
damage to the brain as the parasitized blood cells may block the narrow blood vessels, why
instant treatment is essential. The other types of malaria; 3YLYD[ 3RYDOH and 3 PDODULDH are
normally not life-threatening but very young children or old and sick people are vulnerable.
(WHO, 1997) Malaria is particularly dangerous during pregnancy when it can cause severe
anaemia. (WHO, 1998)

Where there is no significant fluctuations from one year to the next in the transmission of
malaria, people are infected so frequently that they develop a degree of immunity. They can
carry the parasite without showing any symptoms. (Martin, 1995)

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Today, malaria exists in about 100 countries or territories all around the world and the illness
is responsible for 1.1 to 2.7 million deaths each year (alone or in combination with other
diseases). The regions in which malaria is active are extensively centred around the equator,
which also are some of the most heavily populated areas of the world. (WHO, 2000a)

The situation is most severe in Africa, south of the Sahara, where almost half of all the
affected countries are situated, followed by parts of Asia and Latin America. (McCarthy et al.,
1999) In Africa alone, the illness kills one out of every twenty children below the age of five,
a total of 1 million children. The disease is also a common cause of school absenteeism, and
has a negatively impact on the long term learning capacity. For adults mortality rates are
lower, but the illness may reduce the quality of life for chronic sufferers, with frequent attacks
of fever. (McCarthy et al., 1999) Death, by people in countries outside sub-Saharan Africa, is
mainly non-immune people, infected with 3IDOFLSDUXP in areas without available treatment.
(WHO, 2000a) According to UNICEF the annual direct and indirect cost of malaria in Africa
alone, is US$2000 million and to implement malaria control programmes cost at least
$300,000/nation/year. (WHO, 2000a)

Even though malaria exists in fever countries now compared with the beginning of the 20 th
century (when for example both North America and parts of Europe were affected) there has
been an increasing number of malaria epidemics throughout the world, particular in Africa. It
is not really known why the epidemics have increased but scientists believe that changes in
climate may be one answer. (Martin, 1995) Heavy rains, long periods of increased humidity
and temperature, or more permanent changes in the microclimate due to the development of
irrigation systems, agricultural projects or tree plantations improves the possibility for the
mosquitoes to breed and thus the parasite to multiply. Urban and peri-urban malaria is also
increasing, especially in south Asia and in many areas of Africa. These outbreaks are mainly
due to military conflicts as they lead to movement of people. When refugees move in to
malarious areas they contribute to new malaria outbreaks as they often are unprotected, non-
immune and physically weakened. Other explanations to the increase may be unplanned
development around large cities, as this give rise to appropriate breeding sites for the
mosquitoes. (WHO, 1998)

The knowledge about malaria, in affected areas is markedly low. In a recent survey in Ghana,
half the respondents did not know that mosquitoes transmitted malaria. (WHO, 1998)
This incompetence together with rapid deterioration of malaria prevention and control has
even lead to re-emerging of malaria in areas where it earlier has been eradicated. (WHO,

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Some of the most common or most effective malaria control methods are described in this
chapter. Their impact on the environment and on human health is then evaluated in chapter
five and six. In chapter seven, the costs that arise due to the use of these malaria methods are

 5('8&7,21 $1' &21752/ 2) $'8/7 9(&7256
All today available malaria methods, except the use of drugs, aim on reducing or eliminating
the vectors of malaria, i.e. the mosquitoes. These vectors may be controlled in their aquatic
larval stage or as adults The advantages with trying to control them as adults are that they can
be dealt with in the houses. In addition, when insecticides are used, the residual effects of the
compound last longer indoors, than outdoors, as it is not as affected by light and micro-
organisms. People are also less reluctant to control adult mosquitoes than mosquito larvae, as
the adults present a nuisance to people. (Curtis, 1991)

Personnel protection against mosquito bites is the most important control method to apply, i.e.
to avoid contact with mosquitoes. This is primarily done by wearing appropriate clothing and
by the use of repellents but could also be done by the use of bednets. The effectiveness and
function of bednets and plant extract with repellent properties are described below.

Beyond personnel protection you can control adult mosquitoes with different types of
chemicals. There are four main groups of insecticides used for controlling malaria;
(WHO, 1997) However, this thesis only deals with DDT (an organochlorine) and two
different pyrethroids as they are economically feasible to use in developing countries. DDT is
not only one of the first and most commonly used insecticides but also the cheapest.
Pyrethroids are considered rather safe for humans and for the environment and are not as
costly as most organophosphorus compounds and carbamates. (WHO, 1997)

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Many mosquitoes seek shaded and undisturbed sites for resting. In dry regions, houses are
often suitable sites. In more humid forested areas, mosquitoes do not seem to be dependent on
houses and tend to rest in the vegetation. However, in such areas mosquitoes may still enter
houses to feed, and then spend some time resting indoors before and after feeding.

The behaviour of resting indoors makes it possible to kill the mosquitoes by spraying all
surfaces where mosquitoes are likely to rest with long-lasting insecticides. The persistence of
the compound varies with the kind of insecticide, the dosage applied, the type of surface
sprayed and the climatic conditions. The duration can differ from a few weeks to over a year
depending on these factors. (WHO, 1982) Mosquitoes will come in contact with the
insecticide through their feet while resting and hence disturbed or killed before they have a
chance to feed on human. The insecticide consequently prevent the mosquitoes from
transmitting the disease as it reduces the number of infected mosquitoes that enter the house
and the number that, having bitten infective people, leave the sprayed house.
(WHO, 1995) DDT
DDT has since it was developed, been one of the most important insecticide, all around the
world. It is still probably the cheapest and the most widely employed insecticide for malaria
control. It was discovered in the 1930s by the Swiss chemist Paul Müller as the first
chlorinated organic insecticide. DDT belongs to a class of chemicals labelled Persistent
Organic Pollutant (POPs) which all toxic as well as resistant to degradation.

Indoors house spraying with DDT involves applying a small quantity of DDT on the interior
walls and ceiling as well as other places where mosquitoes are likely to rest. The mosquitoes
get the compound on their feet and death occurs due to irreversible damages to the nervous
system. The insecticide should be applied onset the season of malaria transmission for best
effectiveness. The quantities involved are approximately 2 g/m2 depending on the surface and
the length of the malaria transmission season. The effectiveness of DDT will last
approximately for six months. (WHO, 1982, WHO, 1997)

When discovered, DDT appeared to be the perfect pesticide, as it had a high target contact
toxicity and was considered harmless to mammals and humans. During and after World War

II the use of DDT increased enormously. It was then used both for disease-carrying and crop-
eating insects. DDT was also successfully used to eradicate malaria from some nations
(United States, Europe) and to lower case rates by over 99% in countries like Sri Lanka and
India. In South Africa the use of DDT wiped out two of the most dangerous species of malaria

However, with the publication of the American marine biologist Rachel Carson’s 6LOHQW 6SULQJ
in 1962, suspicion grew that DDT had very harmful effects in nature and several countries
banned the use of DDT in the 1970s. Currently, the only official use of DDT, as specified by
the world health organisation (WHO) is for controlling disease vectors in indoor house
spraying programmes. (WWF, 1999) The spreading of insect resistance together with
environmental damages were the first negative effects to be discovered. In more recent years
the discussion on whether DDT creates a hazard to human health or not has been of great
concern. In May 2001, a treaty was signed saying that the use of persistent organic pollutants
such as DDT should be completely abandoned in time.

A serious obstacle with DDT, as mentioned before, is mosquito resistance. Approximately
fifty years ago, two species of $QRSKHOHV were resistant to DDT. Today this figure has
increased significantly and more than 20 species of important malaria vectors show resistance
Synthetic pyrethroids are a group of insecticides made up by esters of specific acids or
alcohol. Synthetic pyrethroids are nerve poisons, rapidly paralysing the nervous system in the
insects. The insecticide has become widely used both in agricultural control and for disease
vector control, as they are classified as highly toxic to insects and harmless for humans.
(WHO, 1990b) Synthetic pyrethroids are, like DDT, contact insecticides with a repellent
effect on insects and thus prevent mosquito bite as it inhibit feeding and drives insects from
their hiding places. (WHO, 1996) Synthetic pyrethroids are now the most commonly used
alternative to DDT in public health programs, including house spraying. (WHO, 1990b)

Synthetic pyrethroids were produced during efforts to modify the chemical structure of
natural pyrethorid that comes from the insecticidal compounds in pyrethrum, which can be
obtained from the flowers of the plant &KU\VDQWKHPXP FLQHUDULDHIROLXP. Pyrethrum has a

high immediate toxicity but it is too unstable to use as a residual insecticide. (Gilles et al.,
1993) Several synthetic variants were completed in the 1970s, with improved physical and
chemical properties together with a greater biological activity. (WHO, 1990b) Below, when
referring to pyrethroid I am talking about the synthetic form of the compound.

The pyrethroids dealt with are permethrin and deltamethrin, as those are the most frequent
used pyrethroids for mosquito control.

Permethrin, one of the first synthetic pyrethroids with stable residual activity, is a broad-
spectrum synthetic pyrethroid. It is used against a variety of pests, parasites, biting flies and
mosquitoes. In malaria vector control, it is mainly used for indoor-biting mosquitoes.
Permethrin exists as two isomers, cis and trans. The cis isomer is more insecticidal than the
trans isomer and more toxic to mammals. (WHO, 1990a) Solution mostly include both
isomers but in different ratios. However, WHO has not made any distinction between the
different solution ratios in the ’acceptable daily intake’. When using permethrin for indoor
spraying, all sites where mosquitoes are likely to rest should be treated. At a dosage of 0.5 g
permethrin/m3 the compound remains effective for 2-3 months. (WHO, 1997)

Deltamethrin is considered to be the most powerful of all synthetic pyrethroids with a broad
spectrum of control. (Extoxnet, 1995a) It is mostly used on cotton and crops such as coffee
and maize, but it is also commonly used for animal and public health as well as for vector
control. The insect toxicity of deltamethrin is greater than that of permethrin, but deltamethrin
is also more toxic to mammals. As the compound is more powerful than permethrin, a dosage
of 0.05 g/m3 is enough when used for indoors spraying. The effect should last for 2-3 months
Nets have been used for a very long time when protecting people against mosquitopiues and
other bloodsucking insects at night. They have though proven to give insufficient protection
as mosquitoes may enter and bite humans if the nets are torn or not properly tucked around
the bed. Furthermore, there is a risk that mosquitoes feed on humans through the net. In
addition, the net does only protect people when staying under the net. However, if the nets are

impregnated with insecticidal or repellent compound these problems can partially be solved.
(WHO, 1997)

Impregnated bednets originates from Russia where they treated bednets with Lysol in the
1930’s. During World War II, German and American armies used DDT on nets, in order to
prevent mosquitoes and sandflies to enter them. During the last 15 years insecticide treated
bednets have been increasingly used as a method to prevent mosquitoes from biting humans
and thus control malaria. Today, the principal insecticide for treating bednets is synthetic
pyrethroids as they are quick acting and highly toxic to insects. (Pålsson, 1999) Pyrethroid
treated bednets are very efficient as they form a chemical barrier for the mosquitoes, aside
from the physical barrier the net creates. In addition, people underneath the net act as bait as
they release carbon dioxide and body odour, which attracts the mosquitoes. When the
mosquito is trying to feed, it will get killed or at least irritated by the pyrethroid before having
found a hole in the net. The insecticide needed when treating bednets is much less than if
spraying an entire house with the chemical. Also, travellers or nomads can use bednets as they
are readily carried and could be used over beds or sleeping mats outdoors.

                            Fig 3. Available mosquito net models

Pyrethroid treated bednets are widely used in China, Thailand, Latin America and in some
ethnic groups in Papua New Guinea and Africa and they have reduced the prevalence of
malaria disease in many of these localities. (Pålsson, 1999) Several studies on the efficiency
of pyrethroid treated bednets have also been carried out recently. A project in Guinea-Bissau
by Thomas Jaenson and Katinka Pålsson (1997) showed that bites from mosquitoes infected
with 3 IDOFLSDUXP were reduced by at least 78% due to the use of permethrin-impregnated
bednets. Furthermore, people experiencing µGLVHDVH ZLWK IHYHU¶ decreased significantly in
villages provided with i impregnated-treated bednets but not in control villages. The
conclusion of the study was therefore that impregnated nets could be an important tool when
trying to reduce disease and death, due to malaria in Guinea-Bissau. (Jaenson, 1997)
According to WHO, a wider availability and use of treated nets could decrease the malaria
illness among children by half. Presently, only 2% of the African children are protected by
insecticide treated nets during nights. (WHO, 2000b)

Where vectors of malaria mainly bites indoors before people go to bed, impregnated curtains
would be more appropriate then bednets. (Curtis, 1991)

However, the insecticide looses its strength in time, due to washing, frequent handling and a
natural degradation of the chemical. The nets therefore have to be re-treated every 6-12
months, an even more frequently if they are washed. A hand wash in cold, soapy water could
halve the nets initial content of pyrethroids (Curtis, 1991) The impregnation is done by
dipping the net in an emulsion of pyrethroid, which is easy and does not require trained
personnel as for house spraying programs. (Curtis, 1996)

As mentioned in chapter 4.1.1, there are different types of pyrethroid. Permethrin and
deltamethrin are the ones mainly used for impregnating bednets, as well as for indoor house
spraying. Deltamethrin, have a greater insecticidal effect than permethrin and only 0.008-
0.025 g/m2 is needed when re-treating nets (the higher number on cotton and fine-mesh
nettings). (WHO 1997, Jaenson, 1996) This dosage may persist for up to one year even with
one or two washings. In areas where the malaria season lasts for more than six months, the
long-lasting effect of deltamethrin is a major advantage. The main drawback with this
insecticide is that it can cause skin sensational side effects. (WHO, 1996) Permethrin, the
safer pyrethroid of the two, requires 0.10-0.50 g/m2 when re-treating nets. The residual effect
of permethrin remains for approximately six months (WHO 1997, Jaenson, 1996)

When using an insecticide intensely, there is always a risk of insect resistance. In addition to
chemical resistance there can also arise a change in behaviour. The feeding behaviour of the
mosquitoes could for example change, i.e. they feed at another time of the day or at another
place. However, up to now, confirmed cases of resistance in $QRSKHOHV due to impregnated
bednets are rare. In China, impregnated bednets have been used for a long time and neither
resistance nor control failure has emerged. (WHO, 1996)

 %,2/2*,&$/ &21752/ NATURAL PLANT EXTRACT
Already in ancient days people noticed that many plants had substances that defended them
against plant-feeding insects and other herbivores. This observation led to the use of plants
and plant-derived substances for protection against different pests. (Berger, 1994, Pålsson et
al. 1999) Natural pesticide based on these plant extracts was commonly used for controlling
mosquito bites until the development of synthetic organic chemical, such as DDT. The
natural substances then lost its importance, as the new pesticides where both more efficient
and could be produced in large quantities at a low cost. However, as the hazardous effects due
to these synthetic organic compounds now are known, a new interest for natural pesticides has
evoked. (Berger, 1994)

Katinka Pålsson at the University of Uppsala made a study in Guinea-Bissau, West Africa,
where she studied the 
 of plant products. Two products, from indigenous
plants (+\SWLV VXDYHROHQV Poit. (Laminaceae) and 'DQLHOOLD ROLYHUL Rolfe (Caesalpiniaceae))
that traditionally have been used for reducing indoor biting mosquitoes at night, where the
main focus of the study. The result indicates that both plants, when smouldered, are effective
mosquito repellents with more than 74% reduction in mosquito activity. Interviews with the
local people implied that approximately 55% of the people in the area used plant product as
repellents and that many also used it together with bednets. (Pålsson et al., 1999)(Resultat se
Katinkas diagram sid 46). Another study made by Katinka Pålsson, where she compared the
repellent activity of plant products on bednets with those of pyrethroid-treated bednets,
showed that both methods reduced the mean number of mosquitoe bites significantly.
(Pålsson et al., 1999) However, the main focus of these studies is the repellent efficiency of
the plants, not their ability as malaria control methods (Pålsson, pers.comm. 2001)

The Neem tree, $]DGLUDFKWD LQGLFDLV is one of the most promising plants for pest control. It
has been used in kerosene lamps in India, as mosquito repellent and for malaria control. Neem
could also be mixed in coconut oil and used for personal protection. When tested in a forested
village in India a protection of 81-91% from bites of anopheles mosquitoes was obtained.
(Pålsson et al., 1999)

Amelie Berger at the department of entomology, SLU, Sweden claims that natural plant
products is an important resource for local people in the tropics as:
(Berger, 1995)

It is important to consider that it may be difficult to do toxicological tests on plant products
due to the fact that they are not uniform and may consist of different active ingredients, which
vary in concentration from sample to sample. This leads to difficulties if the compounds ought
to be synthesised. (Berger 1995)

 &21752/ 2) 02648,72 /$59$(
Where the breeding sites of Anopheles are sufficiently limited in extent and easy to access,
larval control can make significant contribution to malaria control. However, in order to be
effective as malaria control method, a high percentage of all productive breeding sites within
flight range of the community must be found and effectively dealt with. Furthermore, larval
control only reduces the density of local vector populations; it does not reduce the mosquito's
chance of surviving to the dangerous age at which they can carry sporozoites, i.e. malaria
infection. (Curtis, 1996)

Biological control of $QRSKHOHV involves introducing mosquito pathogens or predators to the
mosquito-breeding site. Viruses, bacteria, protozoa, fungus plants and natural predators such
as larvivorous fish are examples of different vector pathogens and predators. The bacteria,

%DFLOOXV WKXULQJLHQVLV, and larvivorous fishes have been the most promising biological
methods for controlling malaria so far, and are thus going to be described below. (Gilles et al,

 %,2/2*,&$/ &21752/ BTI
%DFLOOXV WKXULQJLHQVLV (Bt) is a facultative anaerobic bacterium with an ability to form
endospores and crystals. The crystals are, if ingested, toxic to certain invertebrates, especially
larvae belonging to the insect order &ROHRSWHUD, 'LSWHUD and /HSLGRSWHUD. (WHO, 1999b)
%DFLOOXV WKXULQJLHQVLV LVUDHOHQVLV (Bti) a subspecies to Bt, is specialised on mosquito and
blackfly larvae while other dipterous like flies and gadflies are unaffected by the bacillus. Due
to the efficiency of Bti, it has been used in large-scale vector control programmes since early
1980s in for example Germany and West Africa. In China it has been used for controlling
mosquitoes by adding it to domestic containers of drinking water.

The effective substance in Bti is an insecticidal crystal protein that may be attached to a spore.
The crystal by itself is not toxic, but when the mosquito larvae ingest it, the crystal becomes
affected by the basic environment (pH 9) in the gut. The crystal dissolves and the proteins are
released. Enzymes then activate the protein and the toxin becomes operative. The activated
protein paralyses the gut and the larva cease to feed. Without food the larvae die within hours
or at the latest after a couple of days. (WHO, 1999b)

Fig 4. Mechanism of toxicity of Bt                       (WHO, 1999b)

The treatment with Bti involves spreading a large quantity of spores and crystals at larval
breeding sites during periods of larval hatching. The typical usage of Bti is restricted to
situations where the breeding habitats are well defined, such as ponds, ricefields, floodwater
situation, lagoons, pastures and urban habitats. Bti are not practical to use when controlling
mosquito vector whose breeding areas are extensive and difficult to access. It is neither very
efficient in heavy polluted waters. (WHO, 1999a) The bacteria have a short residual effect,
and the substance must therefore be applied exactly at the time of larvae hatching in order to
be efficient. It has proven to be difficult to retain the toxin within feeding range of the larvae
for more than a day or two. (Curtis, 1991) As the bacteria not are long lasting, it is necessary
to apply more Bti each time new mosquito larvae hatch, which often involves 2-3 applications
per season. (WHO, 1999b)

Although Bti has been used for mosquito and blackfly control programmes for more than 15
years there is still no documented case of resistance due to %DFLOOXV WKXULQJLHQVLV LVUDHOHQVLV
The complexity of the insecticidal protein and the intermixing of treated and non-treated
populations are most likely the answer why resistance has not occurred (WHO, 1999a)
However, resistance to other bacteria used for similar matter has been detected so the
development of resistance towards Bti could not be disregarded. (Jaenson, 1996) LARVIVOROUS FISH
Another type of biological control method is to enhance the distribution and density of the
larvae’s natural predator, for example by different types of larvivorous fish. Nevertheless, they
can only be used in special situations where the water and other conditions are suitable for
them. Examples of such waters are cisterns, shallow ponds or small streams.

Some of the most successful larvivorous fish species, *DPXVLD DIILQLV (mosquitoe fish) and
3RHFLOLD UHWLFXODWD (guppies) have been planted into artificial or natural bodies of water as
part of disease control programs in many countries. These species are suitable as larvivorous
fish as they prefer mosquito larvae to other types of food and their small size allows them to
access shallow water and penetrate into vegetation Other characteristics of an efficient
larvivorous fish are tolerance towards pollution, salinity and temperature fluctuations.

However, larvivorous fish are not very effective in pond and marshes with very dense
vegetation as they then may have problems finding the mosquito larvae. (WHO, 1997) HABITAT MANAGEMENT
The development of mosquito eggs and larvae require water with particular qualities. In order
to accomplish the maturation of eggs to adults, mosquitoes need still water without any flow
rate and a water body that can persist for about two weeks. Furthermore, the larvae need to be
able to access the surface to breathe. In the beginning of the last century people realised that
mosquitoes could be controlled by managing the environment so that no water bodies of this
quality was available for the mosquitoes. (Curtis, 1991)

Vector habitat management involves permanently or temporarily elimination of wetlands and
water bodies that is being favoured as mosquito breeding sites. This kind of management
played a major role in the eradication of malaria in south-eastern United States by the early
1950s and in Israel/Palestine by the 1960s. It was also one of the malaria control method that
made much of Italy malaria-free before World War II But as wetlands are crucial habitats for
many organisms, this management is often done at the expense of biodiversity. (WWF, 1998)

Road construction, irrigation system, agricultural drainage and flood control are examples of
human engineering that have greatly increased the amount of malaria as it gives rise to
suitable breeding sites for the mosquitoes. (Gilles et al., 1993) These sites have already been
modified by humans and could therefore be usable for vector habitat management without
risking loss of important or rare species. If managing these water bodies by draining or filling
them, fluctuating the water level or removing floating vegetation that act as protection for the
mosquito larvae, the breeding of mosquitoes could effectively be controlled. (Gilles et al.,

A manmade environment that creates enormous breeding sites of malaria vectors is paddy
fields (irrigated rice fields). A vector habitat management of these sites where successfully
applied as early as 1922 in Indo-China by using intermittent irrigation. This is now a well-
known technique in Japan and China and has also been used in Gambia and in Kenya. The
aquatic stage of Anopheles is approximately eighteen days and an intermitting system is
usually conducted as only having water present in the paddy field for 16-17 days at a time.

When the surface-film dries off the larvae die. However, continuous irrigation is considered
necessary during transplantation and ear sprouting in order to obtain a sufficient harvest. In
Gambia and Kenya an 80% larval reduction were obtained with this system. All larvae did not
die, as there were plots that did not dry out completely. The disadvantages with this control
system are that irrigation and drainage ditches have to be rearranged, but once this is done, the
maintenance is not any greater than with continuo irrigation. (Curtis, 1991)

 *(1(7,& &21752/
Genetic control involves rearing of male mosquitoes that are radiated or chemically sterilised
before being released into the wild population, that need to be controlled. The reared males
will compete with the wild males for inseminating the females and thus reduce or eliminate
their reproduction potential Female mosquitoes, like many other insects, mate only once in a
lifetime. If they then are inseminated with sterile sperm they will have no offspring. (Asman
et al, 1981, Curtis, 1985)

Since one cannot prevent wild males from mating with the female mosquitoes a high ratio of
released sterile males to wild males are required to succeed with this ’sterile insect technique’.
A way of getting around this problem is to release the males when the wild population is
naturally low or if that is impossible, reduce the wild population by other means. The method
is consequently most effective if prior killing with insecticides, parasites or pathogens is done.
(Curtis, 1985) According to Jaenson (1996) genetic control is only effective if the mass
release is restricted to specific islands, water bodies or deserts.

There has recently been a breakthrough in genetic control of malaria as a new method of
preventing malaria has been developed in at a university in Cleveland, US. Scientist has there
created a mosquito, which is resistant to the malaria parasite, the 3ODVPRGLXP. The genetically
modified mosquitoes produce a substance that prevents the parasite from propagating. A
professor in molecular entomology at the Keele University, Great Britain regards it as a
highly interesting method for the future. (Ny teknik, 2001)

 (&2/2*,&$/ ,03$&7
In this chapter the control method described in chapter four are being evaluated concerning
their ecological impact.

Controlling malaria by killing mosquitoes, always implies a reduction of both larvae and
adults regardless of which method is used. As mosquitoes are an important source of food for
many animals a reduction in mosquito population may have serious effects for wildlife.
During the following discussion this effect is not taken under further consideration as it are
similar for all described methods.

 5('8&7,21 $1' &21752/ 2) $'8/7 9(&7256

 &+(0,&$/ &21752/ DDT
The negative effects of DDT were first noticed in the 1950s when a connection was found
between functionally defective calves and cows grazing on pastures that had been sprayed
with DDT. In the 1960s, after the release of Rachel Carson’s 6LOHQW 6SULQJ it became apperant
that the qualities of DDT that made the insecticide so effective, also turned out to be negative
in an ecological perspective. (WWF, 1998)

Today, nobody argues about the risk of using DDT for agricultural purposes or spreading it in
mosquito breeding sites. But, still, much is unknown about the movement of DDT applied on
the inside walls of a house. The use of DDT for indoors spraying has usually been considered
as a minor source of exposure. (WWF, 1999) Nevertheless, a mass model, made on the
request by WWF, indicates that 60% to 82% of the DDT that is sprayed indoor ends up
outdoors within 6 months. (WWF, 1999) DDT may leave the houses as it is crystalline and
could flake off the wall and be swept or mopped outdoors. Direct evaporation from walls may
also occur but the risk is minimal.

However, tropical Physicians claim that there is no proof of significant leaching of DDT from
houses. They are of the opinion that the positive effects by the reduction of malaria outweigh
the small risk of DDT leakage. The countries that now use DDT for indoor spraying have a
very low health budget and to ban the use of DDT would endanger human health.

Furthermore they claim that the world-wide residues of DDT and its derivates reflects only
the past agricultural use of the compound and that the massmodel made by WWF requires
further investigations, as it is only based on one bachelor thesis (Curtis et al., 2000b)

If DDT sprayed indoors ends up in nature it is not easily broken down by light, chemical
reactions or by living organisms. Furthermore, DDT and its metabolites, especially DDE,
accumulate in living tissue as a consequence of the chemical’s ability to dissolve in fat. This
bioaccumulation (storage in living tissue) reflects the relationship between how much DDT is
taken into an organism versus the amount that is being metabolised (WWF, 1998). As the
substance move into the cells in living tissue, where it is sequestered into fat, DDT also gives
rise to biomagnifications, an increased concentration of the substance further up in the food
chain. Consequently, the concentration of DDT is much higher in the predators than in their
prey. (Bernes, 1998) The biological half-life of DDT is about eight years; that is, it takes
about eight years for an animal to metabolise half of the amount it assimilates.

DDT is highly toxic to fish and aquatic invertebrates while it is only slightly or non-toxic to
mammals and birds. (Bernes, 1998) Notwithstanding, the first effects of DDT were shown in
top predators such as seals and birds of prey. For example, Peregrine falcon, California
condors and bald eagles with high concentration of DDT started to produce eggs with thin
shells. Soon, researchers found an inverse relationship between weakened eggshells and the
p,p’-DDE residues in eggs. Eggshell thinning leads to egg cracking even under normal nesting
conditions, which results in embryo deaths and a decline in bird populations. Thin eggshells
are due to the effect DDT has on the endocrine system, i.e. the hormones. This endocrine
disruption can also lead to feminisation and demasculination of offspring, as the chemical
affects the sex hormone. Lower birth weight and abortions are other consequences. (WWF,

The breakdown of DDT in soil is very slow, with a reported half-life between 2-15 years.
Breakdown products are DDE and DDD, which also have high persistent and similar physical
properties as DDT. The main routes for loss or degradation are runoff, volatilisation and
photolysis. Studies have shown that volatilisation rates can be high in soils with very low
organic content, such as desert soils. Travel through the atmosphere occurs; for example, high
concentrations of DDT have been found in arctic biota where there has been very little local
use of the substance. This indicates a global transport of DDT. The breakdown of DDT in

water is faster than in soils. The main losses are due to volatilisation and adsorption to water-
borne particles and sediment. (Extoxnet, 1996b). SYNTETHIC PYRETHROIDS
Synthetic pyrethroids kill target insects on contact and through digestion and the toxicity are
comparable to that of DDT. However, pyrethroids are not as bioaccumulativ or persistent in
the environment as DDT and should therefore be a better alternative for mosquito control.
Nevertheless, all pyrethroids are highly toxic to aquatic invertebrates and fish, why water
environments must be protected.

The risk of getting pyrethroid in the environment due to indoor house spraying is difficult to
comment as no studies have been made on this subject. But as pyrethroids are partly
crystalline in room temperatures (20°C-25°C) it could, just like DDT, flake off the walls and
be swept outside. Nevertheless, both deltamethrin and permethrin are rather immobile in soil
and is rapidly degraded. It is therefore not likely that the chemical will accumulate in the
environment or in living tissue. (WHO, 1990b)

Microorganisms break down permethrin quite easily in most soils, except in organic soil
types. Under laboratory conditions a half-live of 28 days has been determined. Further, very
little downward moving of the compound occur as the compound binds strongly to soil
particles. Consequently the persistence of permethrin in soil environments is low to moderate
and the compound is rather immobile. Contamination of groundwater is therefore unlikely.
(Extoxnet, 1996b)

Permethrin disappears within one day from ponds and streams as it is rapidly broken down by
sunlight. It can though persist in sediments for about a week. Moreover, it is not poisonous to
most plants if used as recommended.

Permethrin is highly toxic to aquatic invertebrates and fish during laboratory tests. A
moderate potential to accumulation in these organisms has also been detected. However, in
practical use, no adverse effects have been noticed on invertebrate populations or on fish,
presumably because of the low rates of application and the low persistence of the compound.
Tests made on green algae/cyanobacteria showed that the breakdown products of permethrin

affects the growth of cyanobacteria but is relatively non-toxic to photosynthesis.
Cyanobacteria are significant nitrogen fixing organisms in wet tropical soils. (WHO, 1990a)

Permethrin has a very low toxicity to birds and show no effects on reproduction.

The persistence of deltamethrin in soils is low. The half-life in most soils is 10-20 days. When
tested in laboratory conditions, deltamethrin was practically immobile in soil as
approximately 96-97% of the initial content stayed in the 0-2.5 cm upper soil layer. In water,
deltamethrin is rapidly adsorbed by sediments, taken up by plants or evaporated into air.
There is no data on actual levels of deltamethrin in the environment, but it is expected to be
low, as degradation is rapid and the application dose very small.

Deltamethrin is, as well as permethrin, highly toxic to aquatic invertebrates as well as fish
under laboratory studies. However, deltamethrin does not, under normal conditions of use,
harm fish in the field due to decreasing bioavailability of the compound. Accumulation of the
compound, in fish, may however occur. Death of aquatic invertebrates has also been detected
in field. Furthermore, deltamethrin affects aquatic herbivorous insects, which could lead to an
increase of algae. (WHO, 1990b, Extoxnet, 1996a) Toxicity for bird is very low. (Extoxnet,

In summary, the use of pyrethroids for indoor house spraying programmes is considered
relatively safe as it is rapidly degraded in the environment and as very small quantities are
needed, when controlling malaria. However, it is important that wastage of the chemical is
taken care of. It could by no means be dumped in water environments. INSECTICIDE TREATED BEDNETS
Today, the only available insecticide for impregnating bednets is pyrethroid, which also is
used for indoor house spraying. As may be seen from chapter 5.1.1. pyrethroids are rapidly
degraded and rather immobile in the environment. When treating bednets only a very small
quantity of the compound is needed and there are very small risks of significant pyrethroid
loss from the nets.

When re-treating nets with insecticide, they are being dipped in a pyrethroid emulsion. This
emulsion must not be spilled during the treatment and the wastage cannot not be disposed in
streams, rivers or ponds as it is highly toxic to fish and other aquatic organisms. (WHO,

It is important that old, worn out nets are collected and disposed properly, as there can be
remnants of insecticide in them.

As the plants that are being used for mosquito control grown naturally in the environment,
they do not pose a hazard to the ecological surroundings. Nevertheless, if picking large
amounts of a rare or endangered species, there could be a risk of overexploiting it. Eradication
of plants can have immense effects on species that are dependent on it.

 &21752/ 2) 02648,72 /$59$(

part of the ecosystem, i.e. it occur where no applications of the organism have been made
before It persists in soil as spores, which will have a vegetative growth when enough
nutrients are available. When applying Bt to an ecosystem this vegetative spore can persist for
weeks, months or years as a natural part of the natural microflora. The insecticidal crystal
protein, however, will become biologically inactive within hours or days. (Extoxnet, 1996c,
WHO, 1999b)

When controlling malaria and mosquito vectors, Bti is mainly applied directly to the breeding
site, that is to water bodies. The bacterium rapidly sediments and become unassailable for the
mosquito larvae as they feed at the surface or in the water column. The formula is viable for a
longer period when applied to water bodies without any flow rate.

Bti has been tested in numerous studies both in laboratory and in field, without showing any
adverse effects on birds or on fish. Moreover, Bti demonstrates little, if any, direct toxicity to
non-target arthropods In field studies, however, significant decrease or increase of non-target
arthropod populations has been reported. Some arthropod belonging to the order
'LSWHUD:&KLURQRPLGDH, which are closely related to mosquitoes, have shown to be sensitive to
high dosage of Bti, but they should not be affected by mosquito larvicidal dosages (WHO,
Introducing species into new environments always involves a great risk, as it is almost
impossible to predict the consequences of the introduction. There are numerous examples of
devastating attempts of environmental manipulations of this kind. The dangers involve
driving indigenous species out of competition as well as absence of natural enemies, which
among other things could lead to an uncontrolled spread of the species.

If using larvivorous fish for malaria control it is of utterly importance that only indigenous
fish species are being used and that they are used in isolated water bodies such as cisterns,
ornamental pools etc. Even if used in these well-defined water bodies there is a risk of
humans transporting the fish from these places into more natural waters. HABITAT MANAGEMENT
Controlling mosquitoes by managing wetlands involves permanently or temporarily drainage,
which undoubtedly poses a great threat to biodiversity. The importance of wetlands in a
healthy ecosystem has been recognised only in recent years and there are now alarms of them
disappearing all around the world. (WWF, 1998) Malaria control should therefore not be
conducted through elimination of natural wetlands.

Human engineering such as road construction, irrigation system, agricultural drainage and
flood control, which are suitable breeding sites for mosquitoes, have already being modified
by humans and could therefore be suitable for vector habitat management without affecting
important or rare species. However, it is important to remember that important species may
adapt and become dependent on these manmade environments. Environmental management

should therefore be proceeded by biodiversity surveys as well as careful choice of methods in
order to ensure preservation of rare and unique habitats (WWF, 1998).

The use of intermittent irrigation in rice fields involves great water fluctuations, which not
only affects mosquito larvae but also other organisms that are adapted to these environments.
Fish may however, according to Curtis (1991) disperse to persistent accumulation of water. In
order to understand how different organisms are affected more knowledge is needed.

 *(1(7,& &21752/
Today, there are no known direct ecological consequences due to a genetic control method.
According to Jaenson, (1996) the method is ’environmentally comparatively acceptable’.
However, nobody really knows anything about the long-term risks associated with genetic
changes, as it is a fairly new method.

 ,03$&7 21 +80$1 +($/7+
This chapter deals with the effects the malaria control methods can have on human health,
which mainly involves oral and dermal effects of the different compounds.

 5('8&7,21 $1' &21752/ 2) $'8/7 9(&7256

 &+(0,&$/ &21752/ DDT
There are numerous studies on how DDT affects humans, but there are still lots of
uncertainties about how dangerous it really is. Some studies indicate that DDT may cause a
number of adverse effects in humans, ranging from acute toxicity to cancer (WWF, 1999)
while other give no significant proof of such health risks. (Curtis, 2000b) Symptoms of
acute DDT poisoning include confusion, headache, vomiting and tremors. No illness or
irritation due to dermal exposure has been seen. (WWF, 1999)

It is known that DDT and its metabolites cause endocrine disruption in animals, i.e. hormonal
disturbance. As mentioned in chapter, endocrine disruption affects the sex hormone
and thus the reproduction ability in birds. Humans are not as vulnerable as animals but they

may, when exposed to high doses of DDT, suffer from changes in the ovaries. In exceptional
cases these changes could lead to sterilisation. Furthermore, some believe that pesticides with
hormonal effect, such as DDT, can cause and develop some forms of cancer in humans. There
has for example been studies showing correlation between breast cancer and high levels of the
DDT metabolite DDE. (Bernes, 1998) However, Suzanne Snedeker states in a study on
pesticide and breast cancer risks that the more recent case-control studies do not support this
connection. (Snedeker, 2001) Key et al. (1994) claims that the studies with a positive
relationship between breast cancer and DDE were based on abnormally high DDE residues in
serum of patient dying in cancer. The high level could, according to them, be caused by body
wasting, i.e. mobilisation of DDE from body-fat deposits. (Key et al., 1994)

DDT kills insects by affecting the membrane on the nerve cells, which leads to more powerful
and prolonged nerve signals. Infant exposure to DDT on mice indicated that the pesticide
could cause damages to the learning process and to the memory. As the human central
nervous system still develops after birth there is anxiety whether breast milk with high DDT
level could give these kind of damages in new-born babies. (Bernes, 1998)

The studies mentioned above are not based on people living in houses sprayed with DDT. It is
therefore necessary to do more research in order to know whether indoor spraying with DDT
creates a hazard to the people living in the houses or not. However, it is established that the
concentration in rooms sprayed with DDT is much higher (times three) than outside air. It is
also a fact that fatty food such as milk and butter is susceptible to DDT, why residual DDT
may end up in food and hence be ingested. This fact is confirmed by a report indicating that
women living in areas sprayed for malaria control had higher concentration of DDT in their
breast milk. (WWF, 1999) SYNTETHIC PYRETHROID
Permethrin is moderately or practically non-toxic via the oral route. LD50 in rats are 430
mg/kg to 4300 mg/kg. Dermal exposure is slightly toxic, with a reported LD50 in rats to over
4000 mg/kg. There are no reports on human poisoning cases. However, there are several
reports on complaints of numbness, itching, tingling and burning from exposed workers. The

effects disappear mostly within 24 hours after exposure and there are no indications of
adverse effects, if used as recommended. (WHO, 1990a)

There are no reports on people living in houses treated with permethrin, complaining of skin
sensations or other effects.

There are several reports of dermal poisoning from exposed workers, handling deltamethrin.
Numbness in the face, red rashes on the skin, itching, tingling and burning sensation are the
most common effects. Mostly, these sensations come from neglecting safety precautions such
as using gloves and facemask. Most of them have no long-term adverse effect but disappears
within 5-7 days. (WHO, 1990b)

A study that lasted for two days was conducted on pesticide workers who applied
deltamethrin to the inside walls of houses. None of the workers induced any negative effect.
But during a second trial that lasted for five weeks, most of the workers complained of "heat
around the eyes", "burning of the eyes, "heat in the face" and "tiredness". All the workers
used protective equipment and the spray men used facial masks. (Extoxnet, 1996a)

A few cases of deltamethrin poisoning from ingestion of several grams of the product have
been reported. Oral ingestion may cause nausea, vomiting and muscles cramps. (WHO,
1990b) The acute oral LD50 in male rats range from 128 mg/kg to 5000mg/kg depending on
the carrier and condition of the study (Extoxnet, 1996a)

There are no known reports on complaints from people living in houses sprayed with
When looking on the health risks of using impregnated bednets, both the dipping process
(when retreating the nets) and the risk of sleeping under the nets need to be taken into
account. Barlow et al. (2001) has written an article on the risks associated with deltamethrin,
which the following discussion mainly is based on. No similar reports on permethrin and
bednets have been made, but as mentioned in chapter permethrin is very similar to

deltamethrin and have a lower toxicity. The risk presented below on deltamethrin should
therefore even cover the risk associated with permethrin.

Re-treatment involves soaking the nets into an emulsion of pyrethroid. This can be done
without any trained operatives. A study made by Barlow et al. (2001) presents two scenarios
of treating bednets in an emulsion of deltamethrin. A safe scenario that is an ideal situation
when all the safety procedures are being followed, and a least safe scenario, which are
considered as the worst case. The amounts of the emulsion deposited on the skin are estimated
and compared with the Acceptable Exposure Level (AELdermal) of 10 mg/kg bw/day. The
study indicates that the dermal exposure in both scenarios is well below that of AELdermal.
(Barlow et al., 2001)

The potential risks of sleeping under impregnated bednets involve inhalation of the chemical
and if coming in contact with the net, deposition of residuals onto skin. In addition, if infants
and young children sleep under the net, the possibility of them sucking on the net must be
taken under consideration (Barlow et al., 2001) There are no studies made on airborne
concentration of deltamethrin or permethrin under treated bednets. But according to Barlow
(2001) comparison can be made by extrapolate the result made on cylfluthrin (another
pyrethroid) treated net. This assumption gives figures of 0.0056 mg/m3, which may be
compared with the short-term inhalation study in rats with a no-observed-effect level (NOEL)
of 3 mg/m3. A recent field trial has though shown that some users were sneezing and/or felt
bad smell for 3-7 days after re-treatment of the bednets. One person experienced sore eyes
and a tingling skin during the first night. (Barlow et al., 2001) Studies on the risks emerging
from skin contact with the net indicate that the exposure from sleeping under a bednet would
be 0.03-0.06% of the Acceptable Exposure Level (AEL). However, if calculating with the
maximum amount that possible could be transferred onto skin, the exposure indicates a
potential skin irritation, something that has been confirmed in field trials. The oral exposure
from a child sucking or chewing on the net is at worse, well below the safety margins even if
it occurs every night. Notwithstanding, a bitter agent is added to the pyrethroid emulsion as a
safety precaution. (Barlow et al., 2001)

 %,2/2*,&$/ &21752/ PLANT EXTRACT
There are no known general health effects of using plant extract for malaria control but
dermal effects due to toxic substances in some plants may occur. (Jeanson, 1996)

 &21752/ 2) 02648,72 /$59$(

 %,2/2*,&$/ &21752/ BTI
Bti is considered to be practically non-toxic to humans and animals and the bacteria do not
persist in the digestive system of humans or mammals ingesting it. However, some subspecies
of Bacillus thuringiensis has, under experimental exposure of high doses, caused effects like
nausea, vomiting and colic. (Extoxnet, 1996c)

Workers involved in spraying operations with Bt are exposed to high concentration of the
bacteria. A study of the aerosol exposure showed no serious health problems even though
some of them experienced dry-skin, eye irritation and nasal drip or stuffiness. There are a few
cases of infection where Bt has been isolated. A farmer had an eye infection from having a
splash of a commercial Bt product in the eye. Bt has also been isolated burn and war wounds.

Where Bti have been sprayed over populated areas (for example in USA, Canada and New
Zealand) no or very few harmful effect of the substance have been reported. Bti have even
been added to domestic containers of drinking-water in some Asian countries. No adverse
effects in humans have been reported from these attempts to control malaria. Neither when, at
weekly intervals applying Bti to some African river for blackfly control, have there been any
reports on adverse effects on humans.

According to WHO, it is unlikely that Bti products may pose any danger to humans, provided
the products are free from hazardous non-Bt micro-organisms. (WHO, 1999b) LARVIVOROUS FISH
There is no known health effects due to the use of larvivorous fish in malaria control.

                                              35 HABITAT MANAGEMENT
Permanent or temporally elimination of mosquito larvae breeding sites involves no known
health effects.

 *(1(7,& &21752/
The human health risks due to genetic control should, if there are any, be involved with the
sterilising process as it implies contact with chemicals or possible exposure to radiation.

The purpose of this chapter is to estimate the cost of the above described malaria methods.
Both the actual and ecological costs are considered.

Actual costs arise due to the purchase of pesticides, bednets etc, as well as from salaries for
labour and equipment needed when conducting the control. However, the costs for controlling
mosquitoes differ between countries and regions. As this thesis not concern a specific
location, it is very difficult to calculate the true costs for every method. Nevertheless, where it
is possible to obtain figures, this is done.

Ecological costs are indirect costs that arise as a result of an action that cause damages to the
ecological surrounding. The theory about ecological economics is based on a belief that the
world’s natural resources are finite and that the capacity of the natural environment to absorb
and detoxify waste is limited. (Brännlund et al., 1998) The usual way of estimating the
ecological costs are to ask people what they are ‘willing to pay’ (WTP) for preserving a
resource. But this method may be difficult to use in developing countries, as people’s paying
capability is very low. The ecological costs due to different malaria control methods are
therefore very difficult to estimate and there is no available literature in the subject.
Consequently, this thesis does not evaluate these costs in ready money. Instead, a discussion
will be held to indicate which malaria method involves the highest ecological cost.

 5('8&7,21 $1' &21752/ 2) $'8/7 9(&7256

 &+(0,&$/ &21752/ DDT
When using DDT for indoors spraying the actual costs are equivalent to the cost of the
insecticide and the operational costs, that is the costs for spraying personnel and the
equipment. The cost for the pesticide itself is approximately US $0.08-0.1/m2 each spraying.
(WHO, 1997) In most areas it is enough with one spraying per year.

The operational cost for conducting the spraying varies greatly between different countries.
When conducting a study in Sri Lanka in 1999, the cost for personnel, equipment and
protective clothing was approximately $5 per household per intervention day. (Konradsen et
al., 1999)

The ecological cost that may arise from the use of DDT is mainly the costs for reproductive
dysfunction in higher animals. That is, the costs for a reduction or an eradication of top
predators such as seals and birds of prey. As a loss of these animals affects the whole food
chain, the costs would be considerable. SYNTHETIC PYRETHROID
The direct cost of indoors spraying with pyrethroid is estimated in the same way as for DDT,
i.e. the cost of the insecticide and the operational costs are considered.

If using permethrin, the cost for spraying is approximately US$ 0.15/m2, but the spraying
must be conducted at least twice a year, which means a total cost of about US$ 0.3/m2.
Deltamethrin is more expensive than permethrin, but as less substance is needed and it only
needs to be applied once a year, the cost is approximately the same as when using permethrin.
(WHO, 1997) The labour cost should be equivalent to that of DDT, i.e. approximately US $5
per intervention. (Konradsen et al., 1999) However, permethrin must be applied twice a year,
which doubles the operational costs.

Ecological costs due to the use of pyrethroids should be less than from the use of DDT. The
costs primarily arise if the compound is being dumped, or in another way end up in a water
environment as pyrethroids are highly toxic to aquatic organisms. The costs are then equal to
the cost of the lost organisms. INSECTICIDE TREATED BEDNETS
When calculating the direct cost on the use of impregnated bednets, both the cost of
insecticide for re-treatment and the purchase of the nets must be considered. Mostly, there is
no need for trained personnel during the re-impregnation; these costs are therefore not
included in this estimation. However, if using trained personnel to help during the process, the
operating cost should only be about US$ 2 per intervention, as no equipment is needed.
(Kondradsen et al., 1999)

According to a study in Sri Lanka the cost of insecticide is US$ 20-25/litre, which is sufficient
for about 20 double bednets. (Konradsen et al., 1999) Assuming that two persons are sleeping
under one double net, the cost of the insecticide is US$ 2.5-3/person. According to Curtis (2000a) it is US$ 1 per person for insecticide treated nets. Additional, when Katinka
Pålsson and Thomas Jaenson conducted the study Guinea-Bissau they spent approximately
US$ 1 per impregnated bednet (Pålsson, pers. com). Conclusions that can be drawn from
these estimations are that the cost for impregnating a regular size bednet is about US$ 1-3.

The price of mosquito nets depends on the quality of the net and in what country they are
bought. The preferred non-transparent nets cost the equivalent of about US $10. (Konradsen
et al., 1999) In some countries these imported goods are obtained by inflated prices, for
example in Burkina Faso where the price of these nets is approximately as much as US$ 15.
Nets of less durable material, like nylon, only costs about US$ 2.50 at the international
market. (Curtis, 1991) The life span of a bednet is estimated to about 4-6 years. If we assume
that each family own two nets of preferred quality, it would cost them US$ 0.8-

The cost arising due to the use of insecticide treated bednet are similar to those of indoors
spraying with pyrethroids. Both methods involve handling with deltamethrin or permethrin,
which is highly toxic to water environments. The re-treating of the nets may be a potential

hazard as the chemical may be spilled or dumped in natural waters, such accident would give
rise to high economical costs.

 %,2/2*,&$/ &21752/ NATURAL PLANT EXTRACT
The direct cost from using plant extract for mosquito control should be low or even free
depending on the accessibility of the plant.

The economical costs should be very low, if the plants are used in a sustainable way.

 &21752/ 2) 02648,72 /$59$(

 %,2/2*,&$/ &21752/ BTI
The use of %DFLOOXV WKXULQJLHQVLV LVUDHOHQVLV in mosquito control is a costly method mainly as
the applications has to be repeated after every egg-hatching period. The method also requires
knowledge about where and when the mosquito larvae can be found as well as personnel and
equipment for proficient spread and efficiency. In order to reach areas not assessable from the
ground, the distribution is easiest done from a helicopter. A helicopter is though often an
unacceptable high cost in developing countries. If not using helicopter, the distribution of the
compound is done from land, which implies a lot of personnel and equipment.

The cost of the bacterium depends on if using an aqueous solution ($4.0/hectar) or Bti as
granulates ($25-38/hectar). (Jaenson, 1996)

Ecological costs due to the use of Bti should be quite low as long as the compound is used
according to recommendations. However, if applying more Bti than the approved to a
mosquito-breeding site, non-target arthropod populations can decrease significantly with high
economical costs as a result.

                                               39 LARVIVOROUS FISH
The direct costs of the use of larvivorous fish are low. The cost constitutes of the purchase of
the fish and for the labour of placing them in the water body that need to be treated.

The economical costs of using larvivorous fish can be major, if non-indigenous fishes are
used, as it can lead to absence of natural enemies and uncontrolled spread of the fish. Loss of
indigenous species due to the introduced fish may give rise to unexpected changes in the food
chain and considerable economical costs. However, if the fish are used as recommended in
well-defined waters, the economical cost should be minor. HABITAT MANAGEMENT
The direct costs from managing larvae habitats or breeding sites is mainly due to the
operational cost, which means that the expenses vary greatly between different types of
management. If the management implies creating new ditches and water systems the costs
could be considerable. Other habitat management like filling pits and other manmade
breeding sites are inexpensive and could sometimes be done at community level. (Gilles et al.,
1993) However, almost all types of habitat management only need to be done ones, which
makes this method rather cost-effective. (Adult, 1994)

As habitat management is a treat to biodiversity if used at inappropriate sites. The method can
therefore imply very high economical costs. If only used in manmade water habitats these
costs are significantly decreased but there is still a risk of affecting non-target insect and
hence contribute to indirect costs.

 *(1(7,& &21752/
Genetic control is the most expensive malaria control method. The method requires some sort
of factory for the rearing of mosquitoes and the sterilisation procedure, which can be very
costly. Other costs arising from this method are the expenses around the release of the reared
mosquitoes, which has to be preceded by studies and research on were and when to free the
insects. (Jaenson, 1996)

The ecological costs due to genetic control are as well as the ecological effects, rather
unknown. However, there is today no indication of that this methods would involve high
economical costs.

It is important to remember that malaria is normally a treatable disease. Only severe malaria
caused by 3IDOFLSDUXP often results in deaths. Historically, the bark from the plant cinchona
was used for treating malaria, which in the 1820s were separated and the active-ingredient
quinine was found. (MMV, 2001) During Word War II the important drug chloroquine was
first synthesised and this drug is still the first choice when treating 3 YLYD[ 3 RYDOH, 3
PDODULDH as well as uncomplicated chloroquine-sensitive 3 IDOFLSDUXP infections as it in
cheap and safe. (Virtual naval hospital, 2001) Unfortunately, the resistance to malaria drugs is
widespread, especially to chloroquine.

In order to reduce malaria deaths and diseases and to avoid resistance, early diagnosis and
instant treatment is essential. Absence of adequate health services frequently results in access
to self-administration of drugs, which often lead to incomplete treatment and a spread of drug
resistance among the vectors. (University of Leicester, 2000) New safe, inexpensive and
affordable drugs are badly needed. (WHO, 1998)

If the patient is treated with appropriate drugs, the parasite disappears from the blood and will
be unavailable for the mosquitoes. This means that a well functioning treatment not only cure
affected people, but also helps reducing the transmission of the disease. Unfortunately, all
persons infected with the parasite do not show the symptoms of malaria. In some areas,
including Africa, a very large percentage of people may have malaria parasites yet only some
people (mostly small children and pregnant women) show the symptoms. This means that
even though drug treatment is a helpful technique in controlling malaria, it must be combined
with other methods in order to be real effective. (MFI, 1999)

In last decade considerable progress have been made in search for a malaria vaccine, which
would be a powerful substitute to malaria control. (WHO, 1998) It is however a difficult
challenge as the organism is very complex and has the ability to chance through its life cycle.
Many vaccine developers have therefore focused their efforts on creating a vaccine that limits

the ability of the parasite to successfully infect large numbers of red blood cells. This would
not prevent the infection but would limit the severity of the disease and help prevent malaria
deaths. (MVI, 2001)

There is, as could be seen in this thesis, many different ways of controlling malaria. But is
there a perfect control method? Probably not. The control must instead be adapted for a
certain situation and location. In addition, the solution of decreasing the impact of malaria is
not, in my opinion, to find THE perfect control method but to use the existing in co-operation
in order to slow down the development of chemical and behavioural resistance. A malaria
vaccine would of course be very valuable, primarily as it effectively protects people. A
vaccine would also only interfere with the actual parasite, not the vector, and hence not give
rise to as much effects on the environment, as other malaria methods, if any. However, even if
an excellent vaccine would be developed there is a great risk that people living in the most
affected regions would have problem affording it, such as with malaria drugs today.

If looking at available malaria methods, personnel protection against mosquito bites is
absolutely the first to apply, that is, prevent contact between the human body and the insect.
This is easiest done by the use of protective clothing. However, this kind of cover is almost
never sufficient in malaria areas and sometimes not even realistic if is very hot in the specific
area. Consequently, other protections must also be used. In my opinion, insecticide treated
bednets are to prefer. Today only permethrin and deltamethrin are available for treating nets
but hopefully safer chemical may be developed in the future. The dangers involved with
pyrethroids are the re-treatment process as the chemical is very toxic to aquatic environments
and could cause great damage in natural waters. Natural plant extract can possibly be use
instead or together with the insecticide-treated bednets in order to lower the cost. More
research on the effectiveness of these plants is though necessary.

In high-risk situations such as malaria epidemics it might be necessary with indoors spraying
with an insecticide. But as they pose as treat to the environment as well as to exposed humans
they should only be used sparsely. These sprayings should be conducted as governmental
spraying programmes for best effectiveness. Formulation and methods of application should

be used at the lowest effective concentration and only qualified, trained personnel should
carry out the handling of pesticides. (Jaenson, 1996) It is also important to clearly examine if
the targeting mosquito population prefers resting indoors and hence contribute to malaria
transmission before starting the spraying. In addition, synthetic pyrethroid should be avoided
for indoors residual spraying in areas where insecticide-treated bednets are used, in order to
prevent or delay behavioural resistance (WHO, 1995) When it comes to the question on
whether to use DDT or not, I agree with Thomas Jaenson when he writes, “there seems to be
no justification (apart from economical reasons) for the continued use of DDT”. (Jeanson,
1996) There are today good alternatives to DDT, which have the same lethal effect on

When using larval control such as the use of Bti, larvivorous fish and habitat management
there is always a risk of affecting other organism than the target vector. Bti is also expensive,
as the compound must be spread continuously. Situations were they could be useful are for
example when trying to control urban malaria, as the breeding sites then mostly are confined
to puddles, rubbish-heaps and cornfields.

Genetic control of mosquitoes seems to be environmental friendly malaria method with few
effects on human health. However, the cost is very high and there is not many studies
conducted on it effectiveness on controlling malaria. Nevertheless, genetic control has proven
effective when used for other kind of pests.

Finally, control or eradication of malaria vectors should not be done in natural or semi-natural
ecosystems. In these environments, people should be regarded as ”visitors” who need to adapt
themselves to the natural condition. This might even imply, avoiding entering into
environments that could pose serious risks to health. (Jeanson, 1996)


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