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Epidemiology of Andean Cutaneous Leishmaniasis

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					Epidemiology of Andean
Cutaneous Leishmaniasis

By Bruno F. Casanova O.
Universidad Peruana Cayetano Heredia
Supervised by
E.A. Llanos-Cuentas M.D., Ph.D., M.Sc.
Instituto de Medicina Tropical Alexander
Von Humboldt
When my first class of Andean Cutaneous
Leishmaniasis at the Universidad Peruana
Cayetano Heredia finished, I was really impressed
by the complexity of the epidemiology of this
disease, and the efforts done to control the
infection in Perú.
Epidemiology of UTA is particularly interesting,
because it represents the challenge of controlling,
not just human, but animal factors, and the
abundance of a vector like Lutzomyia. Moreover
it’s also a consequence of the lack of modernity in
some parts of the Peruvian Andes.
  Cutaneous Leishmaniasis in
         Peru (UTA)
• Leishmaniasis is an antrophozoonotic
  infection, caused by the bite of female
  Lutzomyia species in the Peruvian valleys.
• The Andean Cutaneous form of
  Leishmaniasis is called UTA.
• UTA affects children more often than
  adults.
   Endemic Zone of Infection


• Pacific facing and interandean valleys
• Altitude: 800 - 3000 meters above sea level.
           Vectors in Perú

• Lutzomyia peruensis (principal vector)
• Lutzomyia ayacuchensis (in some areas)
• Lutzomyia verrucarum (in some areas).
                 Vectors.
• Female sandfly enters the house to feed, in
  the intradomiciliary type of transmission,
  while most males sandflies remain outside.
• They have limited flight range (they live
  close to the houses) .
• They live in places with adequate humidity
  and temperatures (holes in trees, caves,etc).
 Range of arrival time of Lutzomya in
  Huanchoc-Peru (endemic village)


• Lutzomyia verrucarum :6:40 pm - 9:40 pm.
• Lutzomyia peruensis :6:50 pm - 9:40 pm.
• Arrive earlier in June, July & August
  (specially cold < 9 C).
• Arrive later in April & November ( > 9 C)
 Seasons and vector population
• According to some studies, Lutzomyia
  peruensis, during wet (rainy) season,
  increases intradomiciliary and decreases
  extradomiciliary.
• Lutzomyia verrucarum could increase
  inside the houses during dry season.
             Transmission
• There are different patterns of transmission
  even for villages in the same valley
• In some villages transmission occurs
  mainly inside (mostly when people is
  asleep) and around the dwellings, in others
  transmission is mostly outiside.
   Risk factors inside houses

• Having a chimney (smoke repels sandflies)
• Dry wood stored inside the house (provides
  resting holes for sandflies)
• Holes in bedroom windows.
   Risk Factors around houses

• Houses made of stone also provide resting
  holes for sandflies.
• Unfinished house walls (no facing
  material), permits sandflies to enter more
  easily. (also could represent resting holes)
  Risk Factors around houses

• Houses located close to creeks or
  waterways, provide low temperature,
  moderate humidity and enough flora for
  sandflies.
 High risk activities outside the
             houses

• Cutting wood.
• Irrigating crops at night .
• Living in temporary rural shelters (for
  farming, hunting or lumbering)
   Probable Protective factors

• Living close to a river (probably it’s too wet
  or too windy for breeding)
• Living close to a road: Rate of infection is
  low in places close to asphalted roads
• Kitchen gardens and stored grain: Probably
  because the used of insecticed spraying.
    Animals as risk factors of
         transmission
• Which species are risk factors depend on
  vector preference.
• The full role of domestic animals in UTA
  transmission is not clear understood.
• Their evaluation is problematic because of
  the number of animals, and their patterns of
  behaviour.
      Age and transmission

• No evidence for gender dependent risk
  was found , although there’s evidence
  that children are more affected than
  adults.
       Genetic Susceptibility


• People infected at early age + recurrent
  lesions are more susceptible than those
  infected at a later age + single episode.
      Genetic Susceptibility


• Risk of 2nd. episode of UTA and
  susceptibility to different Leishmania species
  could be influenced by genetic variation in the
  host response.
        Insecticide spraying

• Insecticide house spraying reduced the
  incidence of Leishmania by reducing
  sandfly population.
• The effect of DDT against Leishmania has
  been related to insecticide campaigns
  against Malaria in Perú.
           Vector control.

• Transmission can not be eliminated just by
  reducing sandfly abundance below a given
  threshold, but it can reduce the rate of
  transmission.
 Montenegro Skin Test (MST)

• It’s an indirect method to diagnose
  leishmaniasis. Consists on applying an
  antigen (culture of promastigotes)
  intradermically.
• The test’s results can be seen 48 - 72 hours
  later.
       MST (leishmanin test)
• Sensitivity vary with dose, antigen type and
  storage condition.
• Response to MST could be influenced by
  genetic variation.
• MST could be positive by cross reacting
  infections (glandular TBC, leprosy, lizard
  Leishmaniasis)
    Risk factors to develop a mucous
    lesion, dependent on a primary
            cutaneous lesion.
• Multiple lesions
• Localization: head, chest or inferior limbs.
• Lesion area:
  > 16cm2 is major
  < 4cm2 is minor
• Inadequate treatment ?
       Clinical epidemiology

• Clinical infections may lead to acquired
  immunity.
• MST ( + ) people with no scars may have
  protection against subsequent clinical
  infections .
       Clinical epidemiology


• The majority of cases of recurrent disease
  are the result of relapses more than
  reinfection.
       Subclinical Infections

• It’s not clear if they are due to low parasite
  virulence or dose or low human
  susceptibility.
• Some may represent clinical infections with
  long incubation periods .
               Conclusions
• House spraying can cause reduction in
  incidence but it does not provide a
  permanent solution.
• Risk factors vary regionally for a single
  leishmania species (L.peruviana)
              Conclusions

• New strategies must aim at vector control
  and they must be economically accessible.
• Population must be educated about risk
  factors of infection, and how to avoid them.

				
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posted:4/11/2008
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