Visceral leishmaniasis is a vector-borne tropical disease that causes 500 000 new cases every year. The disease is strongly linked to poverty and 90% of the cases is in the poorest areas of Bangladesh, Brazil, Ethiopia, India, Nepal and Sudan. If untreated, visceral leishmaniasis is lethal.
The range of drugs available for the treatment of visceral leishmaniasis is limited. It includes pentavalent antimonials (Sbv), amphotericin B deoxycholate (AB), lipid formulations of amphotericin B, miltefosine (MF) and paromomycin (PM) – all of which have limitations in terms of toxicity, variable efficacy, price and inconvenient treatment schedules. All are parenteral (AB and its lipid formulations by venous infusion, Sbv and PM by intramuscular injection) except for MF which is administered orally.
Due to the parasite’s drug resistance, the most widely used of these drugs – Sbv – is now of little use in northern Bihar, India, which alone accounts for 50% of the world's burden of visceral leishmaniasis. Resistance to Sbv has resulted from several concurrent factors, including high drug costs and the absence of functioning health systems, which have led to poor compliance and incomplete treatments. Areas such as Bihar where transmission is anthroponotic (inter-human) are particularly vulnerable to resistance in the absence of an animal reservoir. Thus, resistance could also occur with other drugs.