Leishmaniasis: resistance to antimonials

(From: Overcoming Antimicrobial Resistance, WHO publication CDS 2000.2)

Leishmaniasis is an insect-borne disease that is showing resistance to the highly toxic, heavy metal-based antimonials at rates of 64% in some developing nations. Currently, visceral leishmaniasis - otherwise known as Kala-azar - afflicts 500 000 individuals each year in 61 countries in the Mediterranean basin, East Africa and India. The sandfly-transmitted parasite attacks the spleen, liver and bone marrow and is characterized by fever, severe weight loss and anaemia. Left untreated, the disease is fatal. Like multiple drug-resistant tuberculosis, drug-resistant leishmaniasis results when treatment courses are too short, interrupted, or consist of poor-quality or counterfeit drugs. Once infected, victims remain vulnerable to potentially fatal flare-ups throughout their lifetime. As with most infectious diseases, resistant strains flourish in areas where poverty is high, surveillance is low and treatment frequently inconsistent due to limited medical access, inadequate diagnosis, the availability of black-market drugs, and political discord. Active monitoring procedures that could reveal the true extent of the disease are hindered by lack of available funds and civil unrest. In one study, WHO researchers conducting a house-to-house search discovered that the actual rate of infection was 18 times that which had been initially reported.

In the state of Bihar in north-western India, up to 70% of Leishmania cases are non-responsive to current treatments, while in Bangladesh, Brazil - and particularly Sudan (where 90% of all cases originate), resistance continues to grow. In developed Mediterranean nations, drug-resistant leishmaniasis continues to spread as the number of patients co-infected with HIV increases. Those infected with HIV or who are immune-suppressed in any way (as a result of cancer treatments or organ transplants) are likewise vulnerable. Any kind of immune-suppression can potentially increase the number of parasites in the blood, thereby giving rise to the likelihood of transmission through the bite of the sandfly. This cycle facilitates a destructive spiral of greater resistance, higher parasitic levels and increased infection-producing potential.

Conflicts, civil upheaval and climatic change also play a role in the spread of leishmaniasis. During the 1990 Gulf War, some 20 Coalition soldiers became seriously ill with the infection. In Brazil and Turkey, visceral leishmaniasis was virtually unknown until fairly recently. In war-torn Sudan, where the disease has been endemic for centuries, researchers have discovered leishmania inexorably marching north. War, globalization, increased travel, and climatic change place the parasitic infection solidly in the category of emerging diseases with rapidly evolving resistance.

Picture: WHO/TDR. A woman suffering the disfiguring complications of leishmaniasis

Back to the table of contents