Visceral Leishmaniasis Disease Background
Visceral Leishmaniasis (VL), also known as kala-azar in the Indian sub-continent, is caused by the protozoan parasites Leishmania donovani and Leishmania infantum (= Leishmania chagasii), and is a potentially fatal disease with a worldwide distribution, in Asia, East Africa, South America and the Mediterranean region. The parasites are transmitted through the bite of female phlebotomine sand flies and in the human host are obligate intracellular parasites of the reticuloendothelial system, surviving and multiplying in different macrophage populations. In patients who develop symptoms, presentation is insidious with development of splenomegaly, irregular fevers, anaemia, pancytopaenia, weight loss and weakness occurring progressively over a period of weeks or even months. Almost all clinically symptomatic (non-immune) patients die within months if untreated. Sub-clinical infection in partially immune human carriers may be an important reservoir of infection. Other mammals, often canids, either domesticated or wild, act as an additional zoonotic reservoir of infection especially of L. infantum.
Visceral leishmaniasis persists today in poor, remote, and in certain politically unstable areas, where there is limited health care and patients have little access to affordable medications. Half of clinical cases occur in children. It is estimated that about 90% of the 50,000 to 90,000 new cases arising each year occur in the rural areas of India, Sudan, South Sudan, Kenya, Somalia, Ethiopia, and Brazil, and that only 30% of cases are reported. Epidemics with high mortality in both adults and children occur, and have, in some areas, been associated with mass movements of non-immune populations from or into endemic areas, as occurred in the Sudan in 1990’s, with hundreds of thousands of lives being lost. Of increasing concern is that visceral leishmaniasis co-infection with HIV is causing the disease to spread into previously unaffected areas of southern Europe, Ethiopia, and India.
Chemotherapy remains the most important element in the control of anthroponotic visceral leishmaniasis. Definitive diagnosis is invasive and is still based on demonstration of the parasites in biopsy material. Recently introduced dipstick diagnostics (antibody based) offer considerable improvement in case finding and epidemiology, but have a limited role in determining drug efficacy and cure. In all areas visceral leishmaniasis control is limited by patient access to treatment centres with trained staff (especially in rural Africa), as well as cost and availability of drugs. The recent introduction of an oral treatment for visceral leishmaniasis in India, miltefosine, has raised hopes for improved treatment, but at the same time also raised concerns about safety, patient compliance and possible sub-optimal use leading rapidly to the development of resistance.
Better diagnostics, particularly based on antigen rather than antibody, which are simple to use and non-invasive, together with a safe, efficacious and affordable short course treatment could lead to effective disease control. The political will of afflicted countries and the required infrastructure are other key factors needed for elimination of kala-azar as a public health problem.