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.