Appendix B cquired immunity by benbenzhou


Appendix B cquired immunity

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									A Guide to
Malaria Management
in the oil and gas industry

Primary prevention of transmissible vector-borne diseases

     In order to rationally design and implement effective primary prevention strategies, a basic under-
     standing of malaria biology, pathophysiology and epidemiology is essential. Over the past 100
     hundred years, there has been a vast experience with malaria.While this knowledge base is far from
     perfect and constantly changing, there is a strong foundation of basic scientific and medical
     knowledge that can be used for successful programme development and implementation.

     In the natural environment, malaria parasites are spread by the infection of two specific hosts:
     mammals (particularly humans) and the adult female mosquitoes of the Anopheles genus.
     Anophelines are found worldwide except on the Antarctica continent.There are approximately 430
     species of Anopheles mosquitoes but only about 30-70 play an important role in worldwide human
     malaria transmission (See Figure B-1)

     The key Anopheles mosquitoes capable of carrying and transmitting the different forms of malaria
     are known as vectors. Hence, malaria is known as a vector-borne disease. Many anophelines are
     inadequate malaria vectors since the parasites either do not or poorly develop within the mosquito.
     This general ability for the different Anopheline species to serve as effective malaria vectors is known
     as vector competence. Vector competence is specific for a given combination of mosquito and
     parasite such that a mosquito may be ‘permissive’ for one species of Plasmodium but ‘refractory’ for
     another. Vector competence is not the same as vector efficiency which refers to the capacity to
     sustain malaria transmission at low levels of vector population.There is a marked difference in both
     the vector competence and efficiency across different anopheline species. These differences are
     extremely important when vector control strategies are considered.

     Anophelines are still found in many areas where the parasite has been eliminated; hence, there is still
     a risk of disease reintroduction in many areas that are ‘malaria-free’. Unlike the situation seen in
     many vector-borne diseases, in malaria the mosquito host is seemingly unaffected by the presence

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                          Annex B: Primary prevention of transmissible vector-borne diseases

    Figure B-1: Anopheles vector worldwide

    of the parasite. However, there are factors that can significantly affect the ability of the mosquito to
    transmit malaria:

    (i) innate susceptibility of the mosquito host to Plasmodium;
    (ii) preferred source of a blood meal, i.e. human versus other mammal; and
    (iii) lifespan, i.e. whether the mosquito actually lives long enough to allow for efficient and
          effective parasite development and transmission.

    Life cycle of malaria
    The major factors that determine the occurrence of malaria are directly based on the malaria life
    ● Anopheles mosquitoes must be present and in contact with humans such that the parasite life
       cycle within the female mosquito can be completed;
    ● Humans must be present and in contact with female Anopheles mosquitoes such that once
       transmitted by the female mosquito the parasite life cycle within the human can be
    ● Plasmodium parasites must be present.

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                                         Annex B: Primary prevention of transmissible vector-borne diseases

              There are rare circumstances where the malaria parasites can be directly transmitted from one
              person to another:
              (i) mother to child or ‘congenital malaria’;
              (ii) blood transfusion contaminated by the appropriate parasite form;
              (iii) organ transplant; and
              (iv) shared needles.

              Anopheles female species require blood meals as a source of protein for the production of eggs.Two
              critical factors are:
              (i) source of blood meals; and
              (ii) feeding and resting behaviour pattern of the mosquito.

              The degree to which the Anopheles species prefers to obtain the blood meal from a human or other
              mammal is a crucial parameter for understanding malaria transmission. Anopheles species that prefer
              human blood are known as anthropophilic while those species that prefer other mammals are
              known as zoophilic. In Africa, the two most important Anopheles species (A. gambiae and A. funestus)
              are strongly anthropophilic and are extremely efficient malaria vectors.

              Feeding and resting behaviour refers to the activity cycle, i.e. dusk or dawn versus nocturnal (night-
              time), primary location of feeding and post feeding resting, i.e. indoors versus outdoors. There are
              very specific scientific terms that are used to describe these behavioural patterns:
              ● Activity—crepuscular (active at dusk or dawn) or nocturnal (active at night);
              ● Feeding—indoors (endophagic), outdoors (exophagic);
              ● Resting—indoors (endophilic), outdoors (exophilic).

              These activity, feeding and resting behaviours have a significant impact on both the overall vector
              efficiency and the analysis of potential control measures, e.g. insecticide treated bednets (nocturnal
              endophagic), indoor residual spraying (endophilic), or source reduction (exophagic/exophilic).
              Table B-1 presents the critical biological behaviours information that is typically obtained for the
              most important malaria vectors.

  Table B-1 An example of biological information related to vectorial efficiency of the three important malaria vectors
  Species        Resting sites                 Biting sites                  Human blood index (HBI) *                               Sporozoite infection rate **
                 Outdoors      Indoors         Outdoors       Indoors        Outdoors     In houses occupied with:
                                                                                          human only       mixed †     unspecified
 Arabiensis      frequently    more            frequently     more             0.08           0.84           0.42         0.72                    2.79
                               frequently                     frequently

 Gambiae         less          most            less           more             0.04           0.89           0.81         0.88                    6.33
                 frequently    frequently      frequently     frequently

 Funestus        rarely        almost          less           more             0.47             –             –           0.98                    3.85
                               exclusively     frequently     frequently

* Proportion of female mosquitoes found fed on human blood = percentage Human Blood Index (HBI)
** Proportion of female mosquitoes found containing malaria sporozoites in their salivary glands = percentage sporozoite rate    † Occupied by humans and animals

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                           Annex B: Primary prevention of transmissible vector-borne diseases

    This type of table is a useful tool and can be constructed for key Anopheles vectors in any
    geographical location. Appropriate control strategies can then be developed in order to lower the
    vector efficiency of the target Anopheles species.

    Once a human is infected by the malaria parasite, a well-understood growth and development
    cycle begins (Figure B-2). In humans, the parasites grow and develop first in the liver (in a form
    known as a ‘merozoite’) and then in the red blood cells (RBCs). The parasite grows within the
    RBC and produces 8–24 daughter cells that are released into the bloodstream when the RBC
    ruptures and is destroyed.These newly released parasites are free to continue the cycle by invading
    other red blood cells. Figure B-2 (Parasite Life Cycle) illustrates this process. The typical clinical
    symptomatology, e.g. fever, sweats and chills, is most commonly caused by the RBC stage of
    malaria infection. Severe clinical effects, e.g. cerebral malaria that can progress to death, can occur
    at this stage. During the RBC stage some of the parasites differentiate into male and female forms
    called ‘gametocytes’.When a female Anopheles mosquito feeds on an infected person the mosquito
    ingests the gametocytes. Inside the mosquito the gametocytes undergo further differentiation and
    development. Eventually, these parasites grow into a form known as a ‘sporozoite’ and migrate to
    the mosquito’s salivary glands where they can be injected into the blood stream of a person.
    Anopheles species vary in their intrinsic sporozoite rate, which significantly affects their vector
    efficiency. The newly injected sporozoites migrate to the liver where they reproduce. A single
    sporozoite can produce 30,000–40,000 daughter cells within six days, and eventually rupture from
    liver cells and re-enter the blood stream and invade RBCs.This completes the life cycle.

    Figure B-2: Parasite life cycle

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                      Annex B: Primary prevention of transmissible vector-borne diseases

Thus, two separate bites are required to perpetuate the life cycle of the parasite and maintain trans-
mission. Individuals remain potentially communicable as a function of the different parasite species:
(i) P. vivax and P. ovale: 1–3 years;
(ii) P. malariae: up to 3 years; and
(iii) P. falciparum: less than 1 year.

The mosquito stays infected for its lifespan.

Many of the clinical symptoms and disease impacts are based on an understanding of this life cycle.
The different Plasmodium species (e.g. vivax and ovale) have subtle but critical biological variations
during the liver phase. Both P. ovale and vivax can remain dormant and persist in the liver for weeks
or even years, in a form known as a ‘hypnozoite’. This explains why infected individuals can have
symptomatic relapses weeks or even years later. In expatriates, these episodes may not be initially
recognized as malaria and can be associated with a delay in diagnosis and treatment. A symptomless
interval of two years for P. vivax and four years for P. ovale years is not uncommon.

Knowledge of the life cycle, both within the mosquito and the human, provides insight into the
transmission dynamics of malaria. For example, the successful development of the parasite within
the mosquito depends on several critical factors:
(i) ambient temperature and humidity; and
(ii) whether the mosquito survives long enough for parasite to complete its cycle within the host

Higher temperatures and humidity (greater than 60%) accelerate parasite growth within the mosquito.
Depending upon both the species and temperature, the mosquito host cycle (known as the ‘extrinsic or
sporogonic’ cycle) lasts for approximately 10–21 days.The optimal temperature for P falciparum is 30˚ C
(86˚ F). At temperatures, below 20˚ C (68˚ F) Plasmodium falciparum cannot successfully complete its
growth cycle in the mosquito and transmission is interrupted. Similarly, the optimal temperature for
P vivax is 25˚ C (77˚ F) while temperature below 15˚ C (59˚ F) adversely impacts the growth cycle.

An adult female typically lives 1–2 weeks in the wild. Estimates of daily mosquito survivorship have
been made for several critical anopheline species. Daily survivorship rates of 77–84% are observed.
This means that approximately 20% of the population is dying on a daily basis.Therefore, less than
10% of the female mosquitoes would survive longer than a 14-day extrinsic cycle. However, if daily
survivorship slightly increased to 90%, then over 20% of the mosquitoes would survive longer than
the typical 14-day extrinsic period. Therefore, control measures (e.g. indoor residual spraying) that
impact mosquito longevity can have a significant effect.

Geographical areas that have both higher temperatures and humidity tend to have more intense
malaria transmission since the mosquito host cycle is faster and more efficient. Conversely, settings
that have wide temperature and humidity swings tend to have less intense and stable transmission
but may be subject to explosive episodes of transmission when ambient conditions become more
favourable.These life cycle and climate interactions help predict:
(i) which geographical environments are likely to be impacted; and
(ii) how changes in rainfall and temperature modulate and predict upswings or declines in
     malaria transmission.

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    All of the typical symptoms that are clinically observed in infected individuals are caused by red
    blood cell stage parasites. However, there is an important period of time between the infective bite
    and clinically experienced symptoms. This time interval is known as the incubation period and
    typically ranges from 7–30 days. The shorter incubation periods are associated with P. falciparum
    infection (12 days) while the longer intervals are more characteristic of P. malariae (28 days). P. vivax
    and P. ovale typically have 13 and 17 day incubation periods, respectively. The potential long delay
    between infective bite and symptoms can cause diagnostic problems and place expatriate workers at
    significant risk. As previously described, both P. vivax and P. ovale can produce dormant liver stage
    parasites that can reactivate and produce disease many months after the infective mosquito bite.
    Antimalarials taken for disease prevention (prophylaxis) are usually highly effective; however,
    incomplete drug courses or partially effective medications can also delay the appearance of
    presenting malaria symptoms by weeks or months since the parasite burden is decreased but not
    eliminated and eventually clinical disease is produced.

      Table B-2 Selected characteristics of the four species of human malaria
                                         P. falciparum                  P. vivax           P. ovale           P. malariae
       incubation days                      12 (9–14)                  13 (12–17)         17 (16–18)           28 (18–40)
       (range)                                                    or up to 6–12 months     or longer            or longer

       exoerythrocytic                        5.5–7                       6–8                 9                  12–16
       cycle (days)

       number of merozoites                  40,000                      10,000             15,000               2,000
       per liver cell

       erythrocytic cycle                       48                       42–48              49–50                  72

       red blood cell                  younger cells, but             reticulocytes      reticulocytes         older cells
       preference                      can invade cells of
                                             all ages

       relapses                                no                         yes                yes                   no

       fever periodicity                      none                         48                 48                   72

       febrile paroxysm                      16–36                       8–12               8–12                 8–10
       length (hours)                       or longer

       severity of                          severe in                mild to severe          mild                 mild
       primary attack                     non-immune

    Source: Navy Pocket Guide to Malaria Prevention and Control

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                      Annex B: Primary prevention of transmissible vector-borne diseases

At a population level, biological characteristics and human behavioural traits influence both the risk
of developing malaria and the observed intensity of transmission. The biological characteristics
include specific genetic factors that are associated with red blood cells.

Individuals who carry the sickle cell trait are relatively protected against P. falciparum malaria. This
genetic trait is more commonly found in sub-Saharan Africa. Another genetically controlled factor
is the presence or absence of certain substances, known as antigens, found on the red blood cell
membrane. The most common RBC antigens are the well known ABO (blood type) and Rh
factor. However, individuals who are negative for another set of RBC antigens known as the ‘Duffy
group’ have red blood cells that are resistant to infection by P. vivax. The majority of Africans are
Duffy negative; hence, P. vivax is relatively rare in SSA, particularly in West Africa. However, P. ovale
has taken over this ecological niche in Africa and can infect Duffy-negative individuals.

While certain genetic factors influence the individual susceptibility to malaria infection, the ability
to acquire immunity after repeated attacks of malaria is critical both for the individual and at a
community level. After multiple malaria infections, an individual develops partial protective
immunity. This individual does not have full immunity (e.g. the type of full protective immunity
associated with a vaccination) but rather is described as ‘semi-immune’. Semi-immune individuals
can still be infected by the malaria parasite but do not develop severe disease and generally lack the
usual malaria symptoms commonly associated with typical clinical disease.The concept of partial or
acquired immunity is important and will strongly influence the decision whether to use prophy-
lactic drug treatment (known as chemoprophylaxis) for local workers. Expatriates, regardless of
home country location, are usually considered as ‘non-immune’, since they lack sufficient protective

Even within the same Plasmodium species, there are various strains that are present.This observation
has been well described for P. falciparum and may account for the observation that repeated episodes
of malaria can occur even in individuals who would appear to be semi-immune.The development
of acquired immunity tends to be location specific.An individual from one malaria endemic region
may not be protected in a country that has a different spectrum and intensity of malaria. In order
to maintain effective levels of acquired immunity, an individual must be constantly exposed to
malaria.Therefore, someone who has been considered semi-immune will rapidly lose this immunity
without continuous immune (infected bite) stimulation. This observation is important in order to
develop appropriate and effective chemoprophylactic treatment programmes for individuals who
are no longer semi-immune.

In addition, any condition that decreases the natural immune response places the individual at
increased risk. For example, there are many medical conditions that affect immune response, e.g.
diabetes, HIV/AIDS, etc. These individuals are less likely to develop effective acquired immunity.
Finally, the most common medical condition that impacts immunity development is pregnancy.
Pregnancy is known to decrease immunity against numerous infectious diseases. It has been well
documented that women tend to lose their protective immunity to P. falciparum, particularly during
their first and second pregnancies. Hence, the unborn child is also at increased risk for premature
delivery and low birth weight.

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                               Annex B: Primary prevention of transmissible vector-borne diseases

    Vector epidemiology
    Epidemiology is the study of the incidence, distribution, and control of disease in a population.
    Epidemiology looks at determinants of health-related states or events in defined populations. The
    emphasis on ‘populations’ versus ‘individuals’ is critical and is a key distinguishing factor between an
    epidemiological approach and an individual based strategy. Successful MMP programmes employ
    both strategies in order to build a successful wall of prevention.While the epidemiological focus is
    usually on human groups, the same epidemiologic techniques can also be applied to vector popula-
    tions, i.e. the critical Anopheles mosquito populations.

    The geographical distribution of large-scale malaria is directly related to several key climate factors:
    (i) temperature;
    (ii) humidity; and
    (iii) rainfall.

    The temperature and humidity requirement tends to circumscribe the geographical settings to areas
    that are tropical or subtropical. Rainfall can create areas of standing water that becomes a major
    source of mosquito breeding sites.The Anopheles eggs are deposited at these sites and, in a tropical
    environment, develop in approximately 9–12 days. In a colder climate this time period can increase
    by up to 2–3 weeks. In the absence of rainfall, these critical small-scale sites disappear and adversely
    impact the eggs since they are not resistant to the effects of drying. Conversely, heavy rainfall flushes
    away breeding sites. However, even within areas of relatively stable transmission, there can still be
    striking micro-environmental variations related to altitude, low humidity/fringe dessert conditions,

     Table B-3 Environmental factors which may contribute to local variations in the prevalence of malaria
     Village characteristics      ●   size   ▲

                                  ●   cattle husbandry      ▲   or   ▼

                                  ●   irrigation for agriculture     ▲

                                  ●   closeness of mosquito breeding sites   ▲

                                  ●   control of breeding sites      ▼

     House characteristics        ●   position in village/town
                                  ●   design, e.g.:
                                      • stilts    ▼

                                      • open eaves (see right)       ▲

                                      • curtains       ▼

     Personal protection          ●   bed nets     ▼
     against mosquitoes           ●   coils and plug-ins or other
                                      commercial local products          ▼

                                ▲=    increases        ▼=   decreases

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                      Annex B: Primary prevention of transmissible vector-borne diseases

and the presence of a ‘cool season’. Significantly, these factors can be readily observed, measured and
monitored using modern remote sensing (RS) techniques. The role and application of RS
techniques for malaria programmes will be presented in subsequent sections.

Finally, there are significant human behavioural and sociological factors that contribute to
pronounced small-scale variations in the observed epidemiology of malaria (Table B-3).

Human activity patterns are related to changes in temperature, i.e. during periods of hot weather,
people may sleep outside and increase their exposure to nocturnal Anopheles mosquitoes. Similarly,
agricultural harvesting patterns, when humans might sleep adjacent to fields without netting
protection, significantly increase exposure. Analogously, continuous work operations also increase
the exposure of individuals to nocturnal vectors. Finally, human knowledge, attitudes, beliefs and
practices regarding malaria are important.

Key quantitative concepts: BCRR and EIR
Base case reproduction rate (BCRR)
The quantitative epidemiology of malaria varies dramatically. Malaria exists both as an unstable
form associated with explosive epidemics and in a stable form where transmission is continuous or
regularly seasonal. Associated with these two patterns, there are marked differences in the public
health impacts, i.e. mortality and morbidity and response to control measures. Similar control
strategies may produce quite divergent results.These differences are generally a function of biology
rather than the efficiency of the health services system.This striking observation is related to a key
epidemiological concept known as the basic-case reproduction rate (BCRR). The BCRR is a
measure of transmission and represents the mean number of new cases of malaria to which one case
will give rise directly after a single passage through the vector mosquitoes, under conditions of no
immunity in the human population.With a BCRR of five, one case will produce 5 cases in the next
generation and 25 in the subsequent generation.This pattern will be continuous until all people are
infected. In a highly endemic malaria situation, the supply of uninfected individuals gradually
decreases and acquired immunity considerations become critical. Similarly, if the BCRR falls
below 1.0, the disease will diminish and begin to die out. Therefore, the theoretical goal of trans-
mission control is to achieve a BCRR of less than 1.0.

The BCRR is significantly influenced by three characteristics of the female Anopheles mosquito:
(i) mosquito density;
(ii) man-biting habit; and
(iii) longevity.

Mosquito density is defined and measured as the number of female mosquitoes per human
inhabitant in a specific area.The man-biting habit is the chance that a given female mosquito will
feed on a human on any given day. Mosquito longevity is typically short; however, a sufficient
number of ‘geriatric’ mosquitoes survive and serve as efficient vectors. Since any value of BCRR
greater than 1.0 is consistent with disease spread, it is important to look a BCRR values across
different geographical areas. In SSA, BCRR values in excess of 1,000 are common. In parts of
Asia, BCRR values are 3–5. These rates illustrate the enormous disparity in the worldwide
malaria situation.

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     In SSA, there is an obvious excess capacity for malaria transmission such that stable high levels of
     endemicity are quite common. The extremely high BCRR level also indicates why malaria is so
     difficult to control since an enormous reduction in transmission must be achieved in order for the
     disease to die out. In the high BCRR setting, malaria is ‘stable’ and sudden epidemics are virtually
     unknown.This stable, high endemicity pattern of malaria infection is known as ‘holoendemic’. In a
     holoendemic setting, the pattern of acquired immunity is the key consideration controlling trans-
     mission stability. Therefore, sudden and dramatic influxes of individuals with low or no levels of
     immunity can be disastrous. Similarly, the introduction of large numbers of non-immune expatriate
     workers without adequate protection is invariably associated with dramatic spikes in the incidence
     of malaria within these groups. This observation explains why the sudden introduction of non-
     immune drilling crews under sub-optimal protection routinely causes a significant upsurge in
     reported malaria cases. The identical situation has been observed with the introduction of inade-
     quately protected troops into malarious areas.

     In contrast to the situation of stable malaria, numerous areas around the globe have unstable malaria
     and are prone to sudden epidemics. A malaria epidemic can be defined as a sudden increase in the
     frequency of malaria that significantly exceeds the inter-seasonal variation normally observed. In
     Africa, unstable malaria is most prevalent in the highlands of the eastern and southern parts of the
     continent. In Asia, the characteristics of unstable malaria are different. Unlike the situation in SSA,
     there are a diverse array of Asian mosquito vectors that exhibit different feeding and resting behav-
     iours. While epidemics can appear in countries like India, Sri Lanka, Papua New Guinea, and
     Pakistan, the epidemic spike is less than that seen in Africa.

     P. vivax, a generally less severe form of malaria, occurs more frequently in Asia than in Africa.African
     malaria is dominated by P. falciparum a form that can cause death. In the New World, localized
     malaria epidemics have been reported and as in Asia, are associated with P. vivax transmission.
     Nevertheless, explosive epidemics have been reported in Brazil particularly associated with reset-
     tlement and gold mining activities. In both of these situations, non-immune groups entered into
     areas of seasonally intense malaria transmission. Other malaria epidemics have been reported in
     Columbia,Venezuela, Peru and Ecuador. In general, New World malaria epidemics tend to be in
     localized and isolated areas. Certain former Soviet Republics in Eurasia have also experienced a
     resurgence in malaria epidemics in locations where transmission had been infrequent. Since there
     are significant oil and gas opportunities and operations in many of these Eurasian areas, industry
     operations and activities could be impacted.

     Entomological inoculation rate (EIR)
     Another key concept is related to the numerical method used to quantify the risk of malaria. An
     underlying assumption in most calculations is the assumption that transmission is uniform across a
     defined geographical area. In fact spatial and temporal variations are both prominent and significant.
     Nevertheless, typical risk is measured using an estimate of the ‘entomological inoculation rate
     (EIR)’. The EIR is defined as the number of mosquitoes biting people during the transmission
     season multiplied by the sporozoite rate of the vector population. As previously discussed (see
     Figure B-2) the sporozoite form of the parasite is found in the mosquito salivary gland and injected
     into a human during a blood-feeding encounter.The EIR is often used as a key indicator parameter
     for control strategy development. EIR is the favoured measure for assessing endemicity as well as
     the risk of epidemic development. Annual rates of EIR within Africa demonstrate enormous

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variability ranging from 0.1 to >1000. In SSA, an EIR <10 is found in areas that are characterized
by unstable malaria patterns while EIRs >100 indicate stable transmission patterns. Areas with
EIRs between 10 and 100 will generally have variable endemicity depending upon factors such as
rainfall, vegetation cover, population density and agricultural and land-use patterns. In SSA, annual
P. falciparum EIR data across spatially distinct sites is variable with means of 121 infected bites/year;
however, the range can be quite large (0–884). Local land use is a major predictive variable with
‘rural’ mean values of 146 while urban areas are often ten-fold lower. EIRs in major African cities
typically range from 0–54 as a function of urbanization, spatial location considerations and living
conditions. In contrast to the high annual EIR observed in SSA, EIRs for P. falciparum and P. vivax
are significantly lower in Asian studies and are quite commonly less than 1.0.

Urban malaria epidemiology
The EIR data provide insight into the spatial differences that exist across different geographical
areas. Urbanization has significant vector-host-parasite behaviour effects on malaria risks. See
Figure B-3.

Figure B-3: Conceptual framework—malaria transmission in an urban setting

  Human ecological and                                    Climatic and topographical factors
  environmental factors
                                                         humidity, rain, temperature, slope, soil type
          Land use and
  • land use patterns:
    urban agriculture;
    industry, formal/informal
  • demographic patterns:                     Larval habitat
    density per household;                •   water quality
                                          •   water quantity
                                                                                  Vector density
                                          •   fauna
                                          •   flora                           •   density                Transmission of
       Municipal initiatives
                                          •   predators                       •   species type              malaria in
   • waste management
                                                                              •   fitness                  urban areas
   • water supply/supplies
                                                                              •   life expectancy
   • vector control measures

                                                  Adult habitat
          Individual and                      • flora
         household factors                    • built environment
   •   socio-economic status                  • blood-meal (choice)
   •   housing material
   •   roofing material
   •   daily activities
   •   protective behaviours

Risk factors that are typically associated with rural malaria may be quite different in urban and peri-
urban (areas surrounding cities) settings. Peri-urban malaria rates tend to be higher than adjacent
urban areas. The overwhelming number of published studies regarding malaria risks and interven-
tions have been carried out in rural rather than urban or peri-urban environments. Relatively little
is known about the individual risk characteristics for a city dweller. For example, African urban
dwellers are 10 times less likely to be bitten by a malaria infected mosquito. Nevertheless, the
phenomenon of ‘weekend malaria’ has been observed when city dwellers temporarily visit a rural or

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     peri-urban environment (UN chronicle 1999).This phenomenon could be potentially significant for
     urban expatriate workers who visit the countryside during weekend excursions. In general, urban
     malaria falls into two broad transmission patterns:
     (i) vectors well adapted to city conditions e.g. Anopheles stephensi, the most common urban
          vector of South Asia; and
     (ii) urban settlements that encroach on the rural habitats of vectors not usually found in city

     The latter observation illustrates why there is a general decreasing transition in EIR from rural
     (highest) to peri-urban to inner city. In SSA, mean annual EIRs of 7.1 in city centre, 45.8 in peri-
     urban areas and 167.7 in rural areas have been reported.

     It is not well known if all of the standard malaria prevention, management and control strategies can
     be effectively transferred to urban settings.While there is some evidence that anopheline species are
     adapting to urban aquatic habitats (e.g. water-filled domestic containers, backyard gardens), there is
     concern that misdiagnosis and subsequent inappropriate treatment of malaria is occurring.All fevers
     cannot be presumptively assumed to be malaria in an urban setting. The typical clinical protocols
     that are employed in the countryside may not be valid in the city. Research has shown that over
     50% of the fevers in an urban setting are not laboratory proven malaria despite an initial clinical
     (non-laboratory) diagnosis to the contrary. Within an urban context, the cost-effectiveness of
     standard vector control strategies is also unknown. Many of these concerns have been summarized
     in the 2004 ‘Pretoria Statement on Urban Malaria’.

     Regardless of global setting, urbanization effects are significant and affect anopheline diversity,
     numbers, survival and infection rates with Plasmodium, and biting frequencies. Urbanization
     radically changes mosquito-breeding habitat by both eliminating open spaces and by increasing
     pollution in the remaining spaces.This process has the effect of limiting dispersion opportunities for
     adult mosquitoes. However, there appears to be a general observation that small-scale homegrown
     gardens within city boundaries may provide acceptable microenvironments for the relevant vectors.
     So-called ‘urban agriculture (UA)’ has been acknowledged as a potentially important issue. UA has
     been recognized by the UN Development Programme as an informal sector that provides food
     supply to growing cities while simultaneously contributing to overall improvements in nutrition,
     employment and poverty alleviation. For example, in a large city in Ghana (Kumasi) 90% of all
     lettuce, cabbage and spring onions consumed in the city are produced in the city itself . In order to
     achieve this level of agricultural productivity, a variety of irrigation systems must be developed.
     Many of these systems create ‘rural spots’ within the urban environment that are potential malaria
     breeding sites. Critical Anopheles species have been found in shallow wells dug for irrigation, in
     ditches of furrow systems and in human footprints on irrigated urban farms. These UA areas can
     be identified by high-resolution remote sensing satellite imagery.

     Overall, the striking difference in rural versus urban malaria is noteworthy since many oil and gas
     projects have both ‘field’ and city (urban) staffs with frequent interaction between the two groups.
     A single MMP strategy may not fit the worldwide diversity of operational settings that exists within
     the oil and gas industry. In many industry situations, there are small project staffs located in an urban
     setting; hence, an individual based clinical emphasis is appropriate. However, there are many oil and
     gas projects, e.g. pipelines, which have a much larger footprint and potentially have wider impacts

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                         Annex B: Primary prevention of transmissible vector-borne diseases

that extend across large geographical areas and numerous local communities. In this setting, a
population-based assessment of the annual EIR would provide significant insight into the types of
MMP strategies that might be effective.

Vector control
The general goal of vector control is to reduce malaria transmission by:
(i) decreasing the contact between humans and the relevant vectors;
(ii) reducing the vector population density; and
(iii) changing vector longevity.

Vector control strategies are relevant for more than malaria since there are a large number of
important mosquito-borne diseases that impact human populations, e.g. dengue fever. In general,
there are ten basic methods that are used for all vector-borne diseases, including malaria (see
Table B-4).

 Table B-4 Basic vector-borne disease strategies
 Administer or apply toxicants                           Categories that include drugs for disease prevention or cure, and
                                                         insecticides or inorganic substances that are toxic to either reservoir
                                                         hosts or parasites

 Reduce populations of reservoir hosts                   Malaria can infect both humans and other mammals; In some
                                                         malaria situations, animals are an important reservoir host for
                                                         silently cycling the disease

 Reduce populations of vectors                           Risk to human or animal health is reduced by altering the
                                                         probability of contact with either/or the reservoir host or the vector

 Induce immunity either naturally or artificially to a   Populations can be protected if sufficient levels percentages of the
 pathogen or vector                                      potential hosts are immune. There is no available vaccine for
                                                         malaria. More than 99% of the population would need protective
                                                         immunity in order to prevent transmission

 Modify the environment through a physical change        A primary method of source reduction is physical change in the
                                                         environment so that survival or reproduction of the vector is
                                                         difficult. This strategy requires an understanding of vector ecology,
                                                         population dynamics and vector-borne disease epidemiology

 Avoid areas or activities of high risk, i.e., change    A knowledge of the feeding and resting behaviours of the vector
 behaviours                                              mosquitoes is essential so that human activities can be modified

 Protect the individual or group by a physical barrier   For malaria, this strategy includes bed nets, housing improvements,
                                                         protective clothing or even the use of zooprophylaxis, i.e. the
                                                         situation where the mosquitoes prefer to feed on livestock rather
                                                         than people such that keeping cattle near human living quarters
                                                         reduces the probability of mosquitoes feeding on people

 Use agents of biological control                        This strategy uses other natural predators to control vectors.
                                                         Examples include the introduction of predators, e.g., fish (Gambusia
                                                         species), that feed on mosquito larva
                                                                                                    …continued on next page

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                               Annex B: Primary prevention of transmissible vector-borne diseases

       … Table B-4 Basic vector-borne disease strategies (continued)

       Alter the genome of the vector or vertebrate host               There are ongoing research efforts that are investigating the use
                                                                       and introduction of modified mosquitoes, historically known as the
                                                                       Sterile Insect Technique (SIT). SIT is a species-specific and
                                                                       environmentally non-polluting strategy that relies on the mass
                                                                       rearing, sterilization and release of large numbers of sterile males
                                                                       over a target area. This strategy has been successfully used for the
                                                                       Mediterranean fruit fly and tsetse fly. For malaria, a variety of
                                                                       generic strategies are under development including those based on
                                                                       creation of a strain of the target Anopheles vector that is refractory
                                                                       to the relevant parasite

       Separate age classes of potential hosts                         This strategy most often applies to diseases of livestock. Age class
                                                                       differentiation is important for malaria since young children and
                                                                       infants are the most vulnerable potential host group;

       Test for the presence of the disease agent and                  This strategy is commonly applied to livestock and is quite unlikely
       remove the infected hosts                                       to be useful for malaria.

     From an epidemiological perspective, these ten methods can be classified into three basic strategies
     that are directed towards different links in the overall transmission chain (see Figure B-4).

     Figure B-4 Vector control in malaria

               study the                                  Vector control in malaria                                       Anopheles
               Anopheles                              ‘stopping Anopheles—a moving target’                                response

                                                                                                                     • changes in
                 • identification                                                                                      behaviour
                 • behaviour                                                                                         • resistance to
                 • density                                                                                             insecticides

                                    Vector                          Vector                          Vector-man
                                    density                       longevity                           contact

                                    • environmental                 • chemical                         • personal protection:
                                      modification                    spraying of:                       - clothing
                                    • environmental                   - breeding sites                   - repellents
                                      manipulation                    - resting areas                    - screens
                                    • biological                    • bednet                             - bednets
                                      solutions                       impregnation                     • community protection

     1. Vector density
     Vector density reduction: the most practical methods are based on the treatment of vector
     breeding places. Most anophelines cannot fly more than 4 km from their breeding sites and
     generally remain within 2 km. Larval control (see Table B-5) is critical so that the primary efforts
     are directed toward:
     ● Source reduction by environmental management, i.e. drainage, flushing, filling and altering
         river and lake margins so that they are unsuitable for anopheline breeding. Larvae occur in a
         myriad of habitats but typically prefer clean, unpolluted water that is undisturbed, slow moving

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                      Annex B: Primary prevention of transmissible vector-borne diseases

    or stagnant. Larvae can be found in fresh or salt-water marshes, mangrove swamps, rice fields,
    grassy ditches and small temporary rain pools.Vegetation preferences are variable and some
    species breed in open, sun-lit pools versus more shaded locations.
●   Larviciding using both chemical insecticides and those of biological origin. Larviciding
    programs are generally administered in cycles, which may vary between 2 and 10 weeks.
    Biological means include the use of the toxin Bacilus thuringiensis israelensis and insect growth
    regulators.These methods require regular location identification and frequent applications.
●   Biological control using predators such as larvivorous fish. Observational studies based on
    mosquito counts have found no evidence that growing the citrosa plant and encouraging
    natural predation of insects by erecting bird or bat houses reduce bites to humans from
    infected anopheline mosquitoes.
●   Space spraying of insecticides for rapid reduction of vector density.There are significant
    limitations to this method including difficulty of nighttime application and poor penetration
    of fogs into the daytime resting places of the vectors.

2. Vector longevity
Increase adult vector mortality: these methods attempt to shorten vector longevity and therefore
decrease the probability that the parasite will complete its development. Reduction in the daily
survival rate has a profound effect on transmission. The two primary methods used for decreasing
longevity are:
● Indoor residual spraying (IRS) for indoor (endophilic) resting mosquitoes.
● Community-wide use of insecticide treated nets (ITNs), particularly for ages 0 to 5—if a
   significant percentage of a population within a geographical area uses ITNs there may be a
   substantial reduction of vector survival, density and sporozoite rate.

3. Vector-man contact
Reduction of human-vector contact: this includes all barrier methods such as bednets, improve-
ments in housing (e.g. screening windows, eaves and doors), repellents for skin and/or clothing and
fumigant insecticide dispensers (e.g. mosquito coils);

All of these vector control strategies require careful consideration of sustainability. There is signif-
icant variability in relation to the type and sophistication of operational and overall management
controls that are required. The main considerations are (i) minimum coverage requirements,
(ii) rapidity of impact and (iii) integration of the overall control efforts.

Indoor residual spraying (IRS) is the most widely used (and abused) method of malaria vector
control.The main purpose of IRS is to reduce the survival of malaria vectors entering houses. This
strategy is of little use for control of malaria vectors that rest outdoors (exophilic), particularly if
they also bite outdoors and do not enter the sprayed structure.

Potential resting surfaces of vectors can be sprayed with an appropriate insecticide at a dosage that
is sufficient to remain effective through the transmission season. The first step in selecting insecti-
cides suitable for malaria control is to determine whether a candidate insecticide is effective (i.e.
presence or absence of vector resistance) and whether the formulation available can be safely used.
An understanding of malaria epidemiology and resting behaviour of the vector is crucial in order

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                                          Annex B: Primary prevention of transmissible vector-borne diseases

     Table B-5 Breeding behaviour and possible larval control methods for key African Anopheles vectors
     Types of                                     Breeding site preference                                   Possible larval control methods
     breeding sites                    Gambiae            Arabiensis          Funestus        Larviciding     Source reduction        Environmental management
     semi-permanent rain pools           +++                +++                +                 ++                 +++                  ++

     temporary rain pools                +++                +++                +                 ++                 +++                  ---

     overflow water                      +++                +++                ++                +                  +++                  ++

     roadside ditches                    ++                 ++                 +                 ++                 ++                   +++

     clogged drainage                    ++                 ++                 +                 ++                 ++                   +++

     discarded containers                ++                 ++                 ---               ---                +++                  ---

     discarded tyres                     ++                 +++                ---               ---                +++                  ---

     hoof prints                         ++                 ++                 ---               ---                +                    ---

     small borrow pits                   +++                +++                +                 +++                +++                  ---

     large borrow pits                   +++                +++                +++               +++                ++                   ++

     swamps/marshes                      ++                 ++                 +++               ---                +                    +++

     impoundment                         ++                 ++                 +++               ---                ---                  +++

     lakeshores                          +                  +                  +++               ++                 ---                  ++

     slow rivers                         ++                 ++                 ++                ++                 ---                  ++

     bay shores                          ++                 ++                 +++               ++                 ---                  ++

     full/partial sunlight               +++                +++                +++               NA                 NA                   NA

     vegetation present                  ++                 ++                 +++               NA                 NA                   NA

     vegetation absent                   +++                +++                +                 NA                 NA                   NA

     muddy water                         +++                +++                ---               NA                 NA                   NA

     polluted water                      ---                ---                ---               NA                 NA                   NA
                                    + + + breeds most + + breeds often   + breeds sometimes   + + + most suitable + + more suitable     + suitable
                                    - - - breeds rarely, if at all                            - - - not suitable NA not applicable

                   to properly target the insecticide application in time and space.The potential development of insec-
                   ticide resistance is a common threat to any programme, since all of these programs rely on the
                   continuous or repeated use of indoor residual spraying. Therefore, even if the local vectors were
                   initially fully susceptible, resistance may rapidly develop. Thus, it is very important to periodically
                   monitor vector susceptibility during programme operations.

                   For example, a study of the residual life of typical insecticide treated walls in Mozambique showed
                   100% mortality among mosquitoes placed on treated surfaces during the first hour of exposure.
                   However in succeeding months, the number of dead mosquitoes varied considerably and dropped
                   to 23 % seven months post spraying.The results of this study and other similar investigations illus-
                   trate several key observations:

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                      Annex B: Primary prevention of transmissible vector-borne diseases

1) Any malaria vector control programme is likely to require sustained and authoritative input
   from expert entomologists.
2) All monitoring tools available need to be integrated in a spraying programme.
3) Alternative methods of vector control are more cost effective than an insufficiently supervised
   spraying campaign.

There are important lessons for the oil and gas industry in these study results because (1) initial
success may be followed by subsequent failure and (2) long term sustainability may be a problem
because of development of resistant mosquitoes. IRS requires extremely high coverage in order to
be successful for either individuals or at a community level. Numerous vector breeding, feeding and
resting behaviours interact and impact the likelihood of IRS success. Similarly, larval control
depends upon extremely high coverage since even a few temporary breeding sites may be sufficient
to maintain high transmission levels.

In contrast to many of the difficulties associated with IRS efforts, insecticide treated bed nets
(ITNs) appear to have an inherent simplicity. ITNs operate at both an individual and community
level. As ITN coverage increases, there is an overall reduction on the vector population; hence the
effect on the community is greater than the sum of the individual protection. ITN community
outreach programmes sponsored by a project, while complex, are still likely to be simpler to support
and maintain than a community-wide IRS effort.

Rapidity of impact, like coverage, is a function of individual versus community level considerations. For
example, introduction of ITNs or window screening has an immediate effect for the individual user but
a slow impact at the community level. In contrast, IRS is not immediately protective at the individual
level but can be initially and rapidly implemented across small communities within days; however, long-
term sustainability presents a different set of considerations. Space spraying or ‘fogging’ is the most rapid
method in areas of high population density and, if the proper equipment is available, rapidly imple-
mented. However, space spraying has traditionally been considered an emergency control method and
is unlikely to be the main vector control strategy due to the known limitations of this technique and
the rapid recovery of the vector population. Often fogging efforts are mismatched to the key vector
behaviours, i.e. activity, feeding and resting patterns. A daytime or early evening outdoor fogging
campaign is likely to have minimal impact on nocturnal indoor feeding and resting mosquitoes.

Malaria specific control activities are generally considered within the context of an overall vector
control management programme. It is unlikely that malaria is the only relevant vector-borne
disease; therefore, economy and efficiency of scale can be obtained within the same project areas
and adjacent communities. A significant degree of command, control and communication is
required in order to successfully implement and sustain vector control efforts. Simply due to the
underlying biology of the relevant vectors, these efforts frequently are extended beyond a given
project ‘fenceline’ and into adjacent local communities.Therefore, there is a significant community
outreach and capacity building set of concerns that are important considerations for short-term
success and long-term sustainability. As an overall MMP programme is designed, the need for
integration of malaria control efforts across the entire spectrum of medical, environmental, safety
and sociological concerns is critical.

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                           Annex B: Primary prevention of transmissible vector-borne diseases

     Remote Sensing (RS) and Geographical Information Systems (GIS)
     The use of sophisticated remote sensing and geographical information systems has led to the devel-
     opment of landscape epidemiology, defined as the identification of geographical areas where disease
     is transmitted. Since the distribution of the main vectors of malaria can be predicted by satellite
     imagery, landscape epidemiology is a critical feature that can be used for the development of MMP
     programmes. While there are important small-scale local differences, the overall spatiotemporal
     distribution of the key vectors is largely driven by a variety of physical factors, almost all of which
     can be analysed using remote sensing techniques. Within the oil and gas industry, there is a signif-
     icant experience with these RS/GIS technologies and they are widely used for project
     development and planning, particularly for environmental and social impact assessments. However,
     RS/GIS applications for analysis of potential health impacts have been less frequent. Nevertheless,
     these techniques are a cross-cutting technology that could hold significant promise for the industry
     in terms of developing both risk maps and early warning systems that would significantly influence
     disease prevention, management and control strategies.

     There is no single spatial, temporal, or spectral resolution that is universally appropriate across the
     diversity of malaria transmission geography. However, there are at least 16 different groups of
     physical factors that have been identified as potentially useful for analysing disease-vector habitats
     and human transmission risk via RS imagery. (Table B-6.)

     Each physical factor is an environmental variable that could be related, directly or indirectly, to the
     survival of pathogens, vectors, reservoirs and hosts.This group of factors was not specifically developed
     for malaria; however, the overwhelming numbers of them are applicable for malaria risk analysis:

     ●   Landsat data (30 m resolution) and Meteosat data allow for the mapping of mosquito habitat
         and relying on the spatial analysis of wetness, land surface temperature, elevation and temporal
         analysis of the vegetation index known as NDVI (see Figure B-5).

     ●   High resolution data (0.8 m resolution) is used for creating vector habitat maps.These maps
         can be and combined with working and living locations data so that more precise spraying,
         fogging and larviciding are possible (see Figure B-6).

     Figure B-5 Chad Doba Oilfield—Landsat data (30 m resolution)
                                                                          Sample of NDVI calculation with Landsat,
                                                                          red indicating strong vegetation
                                                    Landsat imagery courtesy of ExxonMobil

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                                   Annex B: Primary prevention of transmissible vector-borne diseases

Table B-6 Potential malaria-related physical factors identifiable via remote sensing imagery
Factor                         Disease                      Mapping opportunity
Vegetation/crop type          Chagas disease                Palm forest, dry & degraded woodland habitat for triatomines
                              Hantavirus                    Preferred food sources for host/reservoirs
                              Leishmaniasis                 Thick forests as vector/reservoir habitat in Americas
                              Lyme disease                  Preferred food sources and habitat for host/reservoirs
                              Malaria                       Breeding/resting/feeding habitats; Crop pesticides vector resistance
                              Plague                        Prairie dog and other reservoir habitat
                              Schistosomiasis               Agricultural association with snails, use of human fertilizer
                              Trypanosomiasis               Glossina habitat (forests, around villages, depending on species)
                              Yellow fever                  Reservoir (monkey) habitat
Vegetation green-up           Hantavirus                    Timing of food sources for rodent reservoirs
                              Lyme disease                  Habitat formation and movement of reservoirs, hosts, vectors
                              Malaria                       Timing of habitat creation
                              Plague                        Locating prairie dog towns
                              Rift Valley fever             Rainfall
                              Trypanosomiasis               Glossina survival
Ecotones                      Leishmaniasis                 Habitats in and around cities that support reservoir (e.g., foxes)
                              Lyme disease                  Ecotonal habitat for deer, other hosts/reservoirs; human/vector contact risk
Deforestation                 Chagas disease                New settlements in endemic-disease areas
                              Malaria                       Habitat creation (for vectors requiring sunlit pools)
                                                            Habitat destruction (for vectors requiring shaded pools)
                              Yellow fever                  Migration of infected human workers into forests where vectors exist
                                                            Migration of disease reservoirs (monkeys) in search of new habitat
Forest patches                Lyme disease                  Habitat requirements of deer and other hosts, reservoirs
                              Yellow fever                  Reservoir (monkey) habitat, migration routes
Flooded forests               Malaria                       Mosquito habitat
Flooding                      Malaria                       Mosquito habitat
                              Rift Valley fever             Flooding of dambos, breeding habitat for mosquito vector
                              Schistosomiasis               Habitat creation for snails
                              St. Louis encephalitis        Habitat creation for mosquitoes
Permanent water               Filariasis                    Breeding habitat for Mansonia mosquitoes
                              Malaria                       Breeding habitat for mosquitoes
                              Onchocerciasis                Simulium larval habitat
                              Schistosomiasis               Snail habitat
Wetlands                      Cholera                       Vibrio cholerae associated with inland water
                              Encephalitis                  Mosquito habitat
                              Malaria                       Mosquito habitat
                              Schistosomiasis               Snail habitat
Soil moisture                 Helminthiases                 Worm habitat
                              Lyme disease                  Tick habitat
                              Malaria                       Vector breeding habitat
                              Schistosomiasis               Snail habitat
Canals                        Malaria                       Dry season mosquito-breeding habitat; ponding; leaking water
                              Onchocerciasis                Simulium larval habitat
                              Schistosomiasis               Snail habitat
Human settlements             Diseases                      Source of infected humans; populations at risk for transmission in general
Urban features                Chagas disease                Dwellings that provide habitat for triatomines
                              Dengue fever                  Urban mosquito habitats
                              Filariasis                    Urban mosquito habitats
                              Leishmaniasis                 Housing quality
Ocean colour (Red tides)      Cholera                       Phytoplankton blooms; nutrients, sediments
Sea surface temperature       Cholera                       Plankton blooms (cold water upwelling in marine environment)
Sea surface height            Cholera                       Inland movement of Vibrio-contaminated tidal water

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                           Annex B: Primary prevention of transmissible vector-borne diseases

     Figure B-6 Chad Doba Oilfield—high resolution imagery (0.8 m resolution)

                                                                                 High resolution imagery courtesy of ExxonMobil

     These techniques can be used to create mosquito free buffer zones around working and living areas.
     Other available published and generally freely available tools include the WHO HealthMapper and
     MARA LITe (Mapping Malaria Risk in Africa Low-End Information tool) software. While
     MARA LITe is specific for Africa, HealthMapper is a general surveillance and mapping GIS appli-
     cation covering information such as boundary maps, key environmental factors (e.g. lakes, rivers,
     elevations), populations, and data on basic health, school and water infrastructures. The initial
     HealthMapper priorities were Africa and South East Asia; however, the effort has been expanded in
     order to cover all regions of WHO.

     RS/GIS Malaria Early Warning Systems (MEWS)
     Early warning systems attempt to predict epidemics before unusual transmission activity.There are
     three general types of malaria epidemics that are caused by a disturbance of an established
     equilibrium between host, parasite and vector:

     ●   Type I: caused by meteorological conditions, e.g., rainfall, temperature, humidity, that
         eventually revert back to the usual baseline conditions;
     ●   Type II: caused by landscape changes or influx of non-immune individuals in areas, triggering
         a new level of endemicity;
     ●   Type III: caused by interruptions in measures that were controlling malaria.

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                                                               Annex B: Primary prevention of transmissible vector-borne diseases

        Due to the periodicity of cycles caused by meteorological factors that predict vector abundance and
        efficiency, Type I epidemics are clearly an appropriate application for RS/GIS techniques. In
        addition, RS/GIS techniques can identify changes in landscape topography and population
        migration (Type II). Finally, since factors like vegetation, drainage and water bodies can be mapped
        using satellite imagery, large-scale environmental breakdowns in vector control can be observed and
        documented (Type III). Figure B-7 illustrates the three-tired approach for long-range forecasting,
        early warning and early detection of malaria epidemics.

        Malaria early warning systems are a natural outcome of sophisticated RS/GIS techniques. For some
        oil and gas industry projects, the ability to predict upswings in malaria activity may be an important
        component of the overall MMP programme. In addition, these techniques are a possible example
        of technology transfer and capacity building that could be provided at a provincial and national

        Figure B-7 Forecasting, early warning and early detection model (RBM, 2001)

                                                                                                                         FLAG 1
                                           Long-range forecasting based on                                              Possible indicatiors: ENSO parameters, medium-range
                                           indirect risk factors (e.g. ENSO paramaters)                                 weather forecasts
                                           Long lead times but low specificity                                          Responses: ensure early warning and detection systems are
                                           Warnings at national/regional scale                                          operational; mobilize resources at the national scale

                                                                                                   SST threshold
                                                                                                   Measured SST
malaria cases—magnitude oif risk factors

                                           Early warning based on monitoring of                                                     FLAG 2
                                           known risk factors (e.g. rainfall)                                                      Probable indicatiors: meteorological parameters
                                           Better lead times and improved specificity                                              Responses: ensure surveillance systems are
                                           Warnings at district scale                                                              functioning and local response reserves prepared
                                                                                                   Rainfall threshold

                                                                                                   Measured rainfall
                                                                                                                                                                                      (Adapted from from de Savagny and MEWS, RBM 2001)

                                                                                                                                                FLAG 3
                                           Early detection of epidemics based on malaria case data
                                           Short lead times but very high specificity                                                         Indicatiors: facility data
                                           Detection at sub-district scale                                                                    Responses: epidemic control measures

                                                                       Case threshold

                                                                       Recorded cases                                                EPIDEMIC

                                                    Year 1                                Year 2                              Year 3                            Year 4

International Association of Oil & Gas Producers (OGP)
OGP represents the upstream oil and gas industry before international organizations
including the International Maritime Organization, the United Nations Environment
Programme (UNEP) Regional Seas Conventions and other groups under the UN
umbrella. At the regional level, OGP is the industry representative to the European
Commission and Parliament and the OSPAR Commission for the North East Atlantic.
Equally important is OGP’s role in promulgating best practices, particularly in the areas
of health, safety, the environment and social responsibility.

London office
5th Floor, 209–215 Blackfriars Road, London SE1 8NL, United Kingdom
Telephone: +44 (0)20 7633 0272 Facsimile: +44 (0)20 7633 2350
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Telephone: +32 (0)2 566 9150 Facsimile: +32 (0)2 566 9159
E-mail: Internet:

International Petroleum Industry Environmental Conservation Association (IPIECA)
The International Petroleum Industry Environmental Conservation Association (IPIECA)
is comprised of oil and gas companies and associations from around the world. Founded
in 1974 following the establishment of the United Nations Environment Programme
(UNEP), IPIECA provides one of the industry’s principal channels of communication
with the United Nations. IPIECA is the single global association representing both the
upstream and downstream oil and gas industry on key global environmental and social
issues including: oil spill preparedness and response; global climate change; health; fuel
quality; biodiversity; social responsibility and sustainability reporting.

5th Floor, 209–215 Blackfriars Road, London SE1 8NL, United Kingdom
Telephone: +44 (0)20 7633 2388 Facsimile: +44 (0)20 7633 2389
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