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Global Health Matters

September - October, 2007  |  Volume 6, Issue 5

Host Factors Such as the Immune Response Play an Important Role in Controlling Leishmaniasis

Leishmaniasis is possibly the most complicated vector-borne tropical disease in the world in terms of etiology and genomics. It is transmitted by the bite of an insect vector, the phlebotomine sandfly. There are no inexpensive drugs to treat the disease and little understanding of its peculiarities.

In humans, leishmania chagasi parasites can produce subclinical infections, atypical cutaneous leishmaniasis (ACL) and visceral leishmaniasis that is potentially fatal if not treated in a timely fashion. L. chagasi parasites that cause both the ACL and visceral disease appear to be genetically similar, which suggests that host factors such as the immune response play an important role in controlling infection, according to a Fogarty-funded study recently published in Parasite Immunology.

The phlebotomine sandfly spreads
leishmaniasis. (Photo: WHO/TDR/)

Leishmaniasis affects vast areas of the Americas and puts millions of people at risk. Those affected by it tend to be the most vulnerable--the poor and indigenous peoples who live in isolated rural areas or in shanty-towns on the fringes of large cities, where access to health services is scarce. It is severely debilitating and exacts an economic toll on individuals and their families, as well as society at large.

ACL causes permanent disfigurement--it is sometimes mistaken for leprosy--while the visceral virus which causes enlargement of the liver and spleen--is often fatal. Young age being a risk factor, children are especially hard-hit by this form.

The research team evaluated the immunologic response in ACL using peripheral blood mononuclear cells of 37 subjects divided into three groups: active ACL cases, asymptomatic cases, and persons with no history of leishmania infection.

The supernatants of stimulated blood mononuclear cells were analyzed for production of:

A child with cutaneous leishmaniasis (left) and two
young boys suffering visceral leishmaniasis with
distended abdomens (right) are examples of the
disease. (Photos: (right) PAHO; and (left)
WHO/TDR/Marsden, Wellcome Trust)

Robust production of IL-10 in response to leishmania stimulation was observed in active ACL cases, compared to low levels in asymptomatic cases and negative controls. Serum levels were not significantly different among the three groups. In addition, ACL cases displayed depressed levels of all cytokines in response to mitogen. Thus, this first characterization of the immune response in ACL suggests a role for IL-10 as well as partial immunosuppression.

Atypical cutaneous leishmaniasis cases display elevated antigen-induced interleukin-10. Rodriguez B, Beatty R, Belli A, Barreto A, Palacios X, Marin F, Harris E. Parasite Immunol. 2007 (6):277-82.

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