Leishmania antimony resistance: what we know what we can learn from the field

Leishmania is the causative agent of various forms of leishmaniasis, a significant cause of morbidity and mortality. The clinical manifestations of the disease range from self-healing cutaneous and mucocutaneous skin ulcers to a fatal visceral form named visceral leishmaniasis or kala-azar. In the absence of any effective vaccine, the only means to treat and control leishmaniasis is affordable medication. The treatment choice is essentially directed by economic considerations; therefore, for a large majority of countries, chemotherapy relies only on the use of cheaper antimonial compounds. The emergence of antimonial therapy failure in India linked to proven parasite resistance has stressed questions about selective factors as well as transmission risk of drug resistance. Unfortunately, in most parts of the world, the frequency of parasite antimony resistance linked to treatment failure is unknown because of a lack of information on Leishmania antimony susceptibility. This information is crucial for addressing the risk of selection and transmission of drug-resistant parasites, particularly in areas where antimony is the only chemotherapeutic alternative. However, the poor knowledge about factors that favor selection of resistant parasites, the multiplicity of the agents that can play a role in the in vivo antileishmanial activity of antimony, and the lack of a standard protocol to diagnose and survey parasite resistance all contribute to insufficient monitoring of antimony resistance. In this review, we discuss on the factors potentially involved in the selection of antimony resistance in the field and discuss on the methods available for its diagnosis.