Visceral leishmaniasis (VL), also known as kala-azar (Hindi for “black fever”), is a deadly parasitic disease that has plagued human beings for at least a thousand years. VL, which is transmitted by the bite of female sand flies, kills as many as 200,000 people every year—more than any parasitic disease other than malaria. The disease is almost always fatal if not treated. 

Ninety percent of all VL cases occur in five countries: India, Bangladesh, Brazil, Nepal, and Sudan. About half of all the world’s cases occur in one state in India—Bihar, just south of Nepal. 

The impact of VL is greatest in poor Bihari villages like Harpur Hardi, where village women work in 110° heat harvesting rice and wheat for about a dollar a day. Here, everyone knows someone who has died of the disease. 

Sitting on a straw mat, a weary but self-possessed woman who looks 60 but is probably much younger recently related a story that is all too familiar in her village. Her only daughter took ill at age 10 with an unrelenting fever, lost her appetite, and became very weak. Although the family did not have the benefit of a formal education, they recognized the signs of kala-azar and were terrified. The family did not even have enough rupees for bus fare to the city hospital—much less the money for a full course of drugs (about $75-$100). Without treatment, the daughter soon died.

Doctors currently use a number of drugs to combat VL. But even the least-expensive of these treatments are still too expensive for the poorest of the poor. To make matters worse, several of the drugs are highly toxic, and some have become ineffective as drug-resistant strains of the parasite have emerged. There are a small number of effective drugs with minimal side effects, but they are far beyond the reach of the vast majority of those who are afflicted with VL. For example, the drug liposomal amphotericin B costs more than $5,000 for a full course of treatment.

Because VL almost always strikes those with the least financial resources, large pharmaceutical companies have had little market incentive to develop new drugs that are safe, effective, and inexpensive. This market problem is by no means unique to VL treatment. Over the past 30 years, 1,556 new drugs were brought to market; only 21 of these drugs target diseases that disproportionately affect the developing world. 

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