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

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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 its also a consequence
of the lack of modernity in some parts of the
Peruvian Andes.
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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.

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Endemic Zone of Infection

• Pacific facing and interandean valleys
• Altitude 800 - 3000 meters above sea level.

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Vectors in Perú

• Lutzomyia peruensis (principal vector)
• Lutzomyia ayacuchensis (in some areas)
• Lutzomyia verrucarum (in some areas).
  
  
  

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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).

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Range of arrival time of Lutzomya in
Huanchoc-Peru (endemic village)

• Lutzomyia verrucarum 640 pm - 940 pm.
• Lutzomyia peruensis 650 pm - 940 pm.
• Arrive earlier in June, July August (specially
  cold lt 9 C).
• Arrive later in April November ( gt 9 C)

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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.

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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.

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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.

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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)

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Risk Factors around houses

• Houses located close to creeks or waterways,
  provide low temperature, moderate humidity and
  enough flora for sandflies.

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High risk activities outside the houses

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

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Probable Protective factors

• Living close to a river (probably its 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.

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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.

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Age and transmission

• No evidence for gender dependent risk was found ,
  although theres evidence that children are more
  affected than adults.

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Genetic Susceptibility

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

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Genetic Susceptibility

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

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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.
  
  
  

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Vector control.

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

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Montenegro Skin Test (MST)

• Its an indirect method to diagnose
  leishmaniasis. Consists on applying an antigen
  (culture of promastigotes) intradermically.
• The tests results can be seen 48 - 72 hours
  later.

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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)

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Risk factors to develop a mucous lesion,
dependent on a primary cutaneous lesion.

• Multiple lesions
• Localization head, chest or inferior limbs.
• Lesion area
  gt 16cm2 is major
  lt 4cm2 is
  minor
  
• Inadequate treatment ?

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Clinical epidemiology

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

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Clinical epidemiology

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

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Subclinical Infections

• Its 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 .

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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)

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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.