Epidemiology & Risk Factors
Leishmaniasis is found in people in focal areas of approximately 90 countries in the tropics, subtropics, and southern Europe. The ecologic settings range from rain forests to deserts. Leishmaniasis usually is more common in rural than in urban areas, but it is found in the outskirts of some cities. Climate and other environmental changes have the potential to expand the geographic range of the sand fly vectors and the areas in the world where leishmaniasis is found.
Leishmaniasis is found in people on every continent except Australia and Antarctica.
- In the Old World (the Eastern Hemisphere), leishmaniasis is found in some parts of Asia, the Middle East, Africa (particularly in the tropical region and North Africa, with some cases elsewhere), and southern Europe. It is not found in Australia or the Pacific islands.
- In the New World (the Western Hemisphere), it is found in some parts of Mexico, Central America, and South America. It is not found in Chile or Uruguay. Occasional cases of cutaneous leishmaniasis have been acquired in Texas and Oklahoma.
The number of new cases may vary or change over time and are difficult to estimate. For cutaneous leishmaniasis, estimates of the number of new cases per year have ranged from approximately 700,000 to 1.2 million or more. For visceral leishmaniasis, the estimated number of new cases per year may have decreased to <100,000, but previous estimates ranged up to 400,000 or more cases. The cases of leishmaniasis evaluated in the United States reflect travel and immigration patterns. For example, many of the cases of cutaneous leishmaniasis in U.S. civilian travelers have been acquired in common tourist destinations in Latin America, such as in Costa Rica.
Overall, infection in people is caused by more than 20 species (types) of Leishmania parasites, which are spread by about 30 species of phlebotomine sand flies; particular species of the parasite are spread by particular sand flies. The sand fly vectors generally are the most active during twilight, evening, and night-time hours (from dusk to dawn).
In many geographic areas where leishmaniasis is found in people, infected people are not needed to maintain the transmission cycle of the parasite in nature; infected animals (such as rodents or dogs), along with sand flies, maintain the cycle. However, in some parts of the world, infected people are needed to maintain the cycle; this type of transmission (human—sand fly—human) is called anthroponotic. In areas with anthroponotic transmission, effective treatment of individual patients can help control the spread of the parasite.