Pests by yantingting


									“Feeling under the weather?”
   Pests: locust plagues
Parasites: worms, flukes and
Diseases: ‘emerging’ viruses
 Locusts and
  in Africa
            Desert Locusts
Locusts eat their own weight
(about 4 g) in plant matter per
day; a swarm may consist of a
billion insects, and 100 swarms
may be on the move during a
plague (eating 400 kilotons per
A swarm can fly 300 km in one
day, remain afloat out at sea
(and take off again), and remain
active even when covered by


                           solitary hopper

gregarious locust

                          Source: BBC website
Last major locust plague (1987-89)
Outbreak: 1967-68.
Drought in Africa in 1970’s and early 80’s produced a
recession in the locust cycle.
Heavy rains in 1987-89. In Jan. 1987 large swarms formed in
Saudi Arabia. Despite the Saudis’ massive control efforts some
of the swarms crossed the Red Sea and gradually moved west to
Mauritania and north to Algeria. Western Sahara had heavy
rains, and threat to the states in North Africa was so grave that
Morocco deployed 200 000 soldiers to combat the swarms.
Strong winds aloft (associated with Hurricane Joan) carried
some of these locusts across the Atlantic to the Caribbean in
October 1988. They reached as far west as Jamaica.
     Upsurges in 1990’s

1996-1998: Local upsurge in Red Sea Basin
     (from Yemen - Saudi Arabia to
   Sudan - Ethiopia - Somalia -Eritrea)

    2004 outbreak
    a) map of outbreak
    b) swarms in Mauritania
    c) Aerial spraying
       in the western Sahara

              Source: BBC website
Monthly snapshots of outbreaks
  from Nov. 2003-Nov. 2004

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 gregarious adults                   gregarious juveniles
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       2004 plague

Rainfall and the                                               Scale of outbreak

 plague locust
                                     Sources: BBC website;;
              Combating locusts
Good news:
•Prediction of swarm development and movements much easier with
satellites which can identify areas of new plant growth and wind
patterns in remote desert areas.
•Aerial spraying of young (pre-swarm) populations with insecticide
(e.g. malathion) is still effective.
•New biopesticide (Metarhizum fungus = “Green Muscle”) kills
locusts and grasshoppers in 3 - 4 weeks.
•Trigger for gregarious behaviour (hind leg stimulation!) recently
identified; may lead to suppression techniques.
•Locusts are more nutritious than beef - “Cooking with Sky Prawns”
(20 recipes for cooking locusts from Australia)
            Combating locusts
Bad news:
•Highly cyclical nature leads to poor maintenance of
surveillance and control equipment during recessions.
•Political conflicts create refuge areas for swarms:
The western Sahara desert is littered with land mines
from the Polisario war.
Morocco-Algeria-Libya are reluctant to cooperate;
The Sudan is currently in the midst of a civil war; locust
control is not a priority for the local government or for
international humanitarian agencies.
        Malaria (Ital: “bad air”)
     1990’s:      2 000 M people at risk
                    300 M are infected
                    110 M cases reported annually
                     (85% in Africa; 7% in SE Asia)
     Deaths:      1 - 2 M annually

Vector: Anopheles mosquito (50-60 spp of the 380 known
         species of anophelines) can carry the parasites.
Parasites: Four species of Plasmodium. P. falciparum causes
most severe symptoms.
Symptoms: high fever, dehydration, death in severe cases
   Global incidence of malaria

Map area equivalent to cases per 100 people (92% of all cases in
The malaria transmission cycle I

The malaria transmission cycle II
After a single sporozoite (the parasite form inoculated
by the female mosquito) of Plasmodium falciparum
invades a liver cell, the parasite grows in 6 days and
produces 30,000-40,000 daughter cells (merozoites)
which are released into the blood when the liver cell
ruptures. In the blood, after a single merozoite invades a
red blood cell, the parasite grows in 48 hours and
produces 8-24 daughter cells, which are released into the
blood when the red blood cell ruptures. These male and
female gametocytes are ingested by the mosquito
during a blood meal, and inoculation of sporozoites
begins again in the mosquito.
  Role of climate in malaria outbreaks
Moisture: Breeding success of mosquitoes is
maximised in nutrient-rich pools; populations
are most abundant in wet weather. Too much
rain, however flushes pools and reduces
breeding success.
At temperatures between 25-30°C the malarial
parasites and mosquito larvae mature quickly,
the adult mosquitoes live longer, and female
mosquitoes feed more frequently.
                                  development of Plasmodium
Length of the life-cycle in

   anophelines (weeks)

                                                    P. malariae

                              2                                   P. falciparum
                                                   P. vivax
                               15             20            25                 30
                                                   Temperature (°C)
                                    minimum                                       maximum
       Sri Lanka (Ceylon):
topography and annual precipitation (mm)




     Summer monsoon
          Malaria epidemic
     Sri Lanka (Ceylon) 1934-5
Malaria hyperendemic in dry north of island but rare
in wet south (heavy rains flush mosquito larvae away).
Southern population has little natural immunity.
Drought in 1934-5 resulted in major epidemic in south.
30% of population fell ill; 80,000 died. Illustrates
Ross’s “math of malaria” (~25d fever cycle)




                       0   25   50   75 days
   The East                                                                                                                        Kericho

                                           Months suitable for P. falciparum transmission
  resurgence:                                                                                        QuickTime™ an d a

   is climate
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   change to                                                                                                                       Gikonko

Hay et al., (2002) Nature 415, 905 - 909
Geography of malaria risk
in N. America (AD 2000)
  Disease and climate change:
a future geography of malaria?
 The demise of
 malaria in the
USA (1918-1946)
Malaria resurgence ….. and decline

       2005-6 ~10 000 cases in South Africa
       2006-7 ~3 000 cases in South Africa
Why was malaria widespread in
 northern Europe in the LIA?
                     Ice Age

from: Reiter, P. 2000. "From Shakespeare to Defoe:
Malaria in England during the Little Ice Age” Emerging
Infectious Diseases vol. 6
  Bilharzia (Schistosomiasis)
• Infection caused by parasitic flatworms [“flukes”]
  in the genus Schistosoma.
• Freswater snails are the intermediate hosts.
  Infection occurs through skin whilst wading in
  water. Eggs released by humans defecating or
  urinating near these bodies of water.
• Victims become emaciated and very weak.
• Common in areas such as the Nile Valley for
  several thousand years. Incidence varies with
  intensity of flooding in (sub)tropical lowlands.
Bilharzia distribution
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                                                           a severe
                                                         of the liver
                                                         and spleen)
                 Lyme Disease
• Infection caused by bacterial spirochetes (Borrelia
  burgdorferi) transmitted by blood-sucking ticks.
• Symptoms include arthritis, heart problems and
  severe neurological/nerve disorders.
• Discovered in USA in 1975 (Lyme, CT)
• Continued to increase and spread since surveillance
  began in 1982.
• Lyme disease has global distribution in temperate
• Complex ecology linked to climate and land-use
                         Deer ticks (Ixodes species)

N.B. - The “dog tick” is not a member of the Ixodes genus and cannot spread Lyme disease
Number of cases of Lyme disease reported in US:
                  1982- 1997
Why has incidence of Lyme disease increased in
     New England in the last 25 years?

• Farm abandonment in early decades of last
• Abandoned farmland undergoes ecological
  succession to oak-maple forest in about 50-
  80 years.
• Expansion of suburban development into
  rural areas around NYC-Boston.
• Reduced hunting of deer?
Lyme disease and the ecology of oak-maple woodlands

                           Mast Year (e.g. 1994)
 Fall                      Winter         Spring                Summer

                  t icks
                                                                     Ticks      Ticks
                                          Ticks       Ticks

    heavy acorn crop         mice BREED    Larval ticks to mice; Nymphs and adult ticks
 attracts deer, provides                  feed, move to shrubs     to humans or deer
  winter food for mice.                      mice emigrate
       Ticks breed

                   Non-Mast Year (e.g. 1995)
        Few acorns few deer         few ticks in oak forests;
        deer stay in maple forests and mice migrate there
            because of over -population in oak forests
Climate and viral disease
      Viral disease transmission

 Ecology of flavivirus outbreaks
(e.g. dengue, West Nile encephalitis)

Ecology of bunyavirus outbreaks
         (e.g. sin nombre)
         Emerging viruses
Family      Disease       Vector and Reservoir
Flavi-    Yellow fever   Mosquitoes (Aedes)
          Dengue         Mosquitoes (Aedes)
          Encephalitis   Mosquitoes+birds
Arena-    Lassa fever    Aerosols+rodents
          Machupo        Aerosols+rodents
          Junín          Aerosols+rodents
Bunya-    Hanta          Aerosols+rodents
          Sabía          Aerosols+rodents
          Rift Valley    Mosquitoes+
          fever          sheep & cattle
Filo-     Ebola          direct? + monkeys
          Marburg        monkeys
       Dengue (hemorrhagic) fever
•   Inter-human transmission of DF by mosquito (esp. Aedes) bites.
    Fever lasts a few days. Complications can give rise to DHF (Fatal
    in >20% of cases if untreated).
•    DF cases common in humid (sub)tropical climates esp. in wet
    season (improved breeding success for Aedes).
World distribution of Aedes aegypti and
        dengue fever epidemics
 Distribution of Aedes aegypti in the Americas


 Prior to yellow    After post-war yellow      Two decades
fever eradication     fever eradication      after eradication
  programme.            programme.          programme relaxed
Distribution of dengue in the Americas

     Prior to       1981-
       1981         1995
           West Nile virus
•West Nile virus is a strain of flavivrus, closely
related to Japanese encephalitis. Previously
reported from Africa and adjacent areas of
southern Europe and western Asia. Previous
outbreaks in Israel, France and S. Africa. and
Romania (1996; 450 cases, 39 deaths).
•It joins at least four other encephalitis viruses
in North America, one of which [St. Louis
encephalitis] is widespread.
•Likely introduced into N. America by an infected
international traveler or as a result of the
importation of exotic birds.
      fever, aches, stupor, (brain
      lesions, coma, paralysis, death?)

direct transmission?
                             WNV cases - Canada
                2002       2003      2004      2005        2006   2007
 Nova Scotia     0          2**        0        1**          0     1**

New Brunswick    0          1**        0        1**          0     0

   Québec        20         17         3         4           1     2**

   Ontario      394         89        13         95         42     12*

  Manitoba       0         142         3         55         50    578*

    Sask.        0         937        5*         58         19    1285*

   Alberta       0         272        1*         10         39    318*

     BC          0         20**        0         0           0    19**

 Yukon/NWT       0          1**        0         0           0     0

  CANADA        414        1481       25        225        151    2215

                       *some related to travel outside province
                       **all related to travel outside province
                 November, 2003

                      Total number of cases
                              by state

                    Is the WNV threat
                  declining in N. America?

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November, 2007
 Resurgence of
WNV in southern

Is this a by-product of
the credit crisis? Have
  foreclosures led to
  increased mosquito
 breeding in neglected
    ponds and pools?

                          L.A. Times (Aug. 6, 2008)
  Ecology of a hantavirus* outbreak

            animal        faeces, urine
           reservoir                         humans
          (esp. mice)

Symptoms first noted in a Chinese medical text dating from about
Major outbreak in Korean War (>2000 UN troops infected).
[*Hantaan is a river in Korea].
Fatal form stretches west to Balkans and into Americas; non-fatal
form in north and western Europe.
    “Four Corners” aka “sin nombre”
• Outbreak began in 1993 in Four Corners area of US
  southwest with three unexplained deaths from
  pulmonary illness amongst local Navajo population.

• Virus identified by CDC as a type of hantavirus.
• Virus endemic in deer mouse populations across
  western states and interior BC.

• Symptoms include high fever, coughing and other
  flu-like symptoms.
• Death rate following infection now reduced to ~40%.
         Ecology of a “Sin nombre” (Hantavirus) outbreak

Winter                              Summer                 Winter          Spring/

                                                           Mice invade   Viral ou tbreaks
         thi ck snowpack                                                 from breathing
                                                            build ings
                                                                          mouse ŅdustÓ
 High moisture availa bility    Large pine seed cro p
    (e .g. El Ni–o year)     rapid increase in deer mice
                             population (x10 in 1995-6)

         Control? Keep mice out of, and away from buildings.

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