Leishmania are tiny protozoa. Their parasitic life cycle includes the sandfly and an appropriate host. Humans are one of those hosts. Leishmania infection can cause skin disease (called cutaneous leishmaniasis).

It can affect the mucous membranes with a wide range of appearance, most frequently ulcers. It may cause skin lesions that resemble those of other diseases including cutaneous tuberculosis, syphilis, leprosy, skin cancer (basal cell carcinoma), and fungus infections.

Leishmania can also cause systemic disease (visceral leishmaniasis) with fatal complications. When introduced into the body by the bite of a sandfly, the parasite migrates to the bone marrow, spleen, and lymph nodes.

Systemic infection in children usually begins suddenly with vomiting, diarrhea, fever, and cough. In adults, fever for 2 weeks to 2 months is accompanied by nonspecific symptoms, such as fatigue, weakness, and loss of appetite. Weakness increases as the disease progresses.

The skin may become grayish, dark, dry, and flaky. The parasites damage the immune system by decreasing the numbers of disease-fighting cells so death usually results from complications (such as other infections) rather than from the disease itself. Death often occurs within 2 years.

Cases of infection by Leishmania have been reported on all the continents except Australia. In the Americas, Leishmania can be found from Mexico south into the South American continent. Leishmaniasis has been reported among some military personnel returning from the Persian Gulf. (See Travelers guide to avoiding infectious diseases.)