One Health: The global challenge of epidemic and endemic leishmaniasis

Visceral leishmaniasis (VL) is a chronic and frequently lethal disease caused by protozoan parasites of the L. donovani complex, order Kinetoplastida. The aetiological agents are: L. donovani in India and Central Africa and L. infantum in the Americas, the Middle East, Central Asia, China and the Mediterranean. The human disease is lethal if not treated early after the onset of clinicopathological abnormalities that include: malaise, anaemia, cachexia, hypergammaglobulinaemia, hepato-splenomegaly and progressive suppression of the cellular immune response. L. donovani complex species are intracellular parasites of macrophages of lymphoid organs such as the spleen, lymph nodes, bone marrow and liver. Their biological cycle alternates between the amastigote form in the vertebrate host and the promastigote form in the gut of the sandfly vector. More than 90% of human cases of VL occur in India, Sudan, Bangladesh and Brazil. Each year 500,000 new human cases of VL are reported [1].Several species of vertebrate mammals may be infected naturally with Leishmania. Canids are the main reservoirs for the viscerotropic species in the Mediterranean, Asia, North Africa and South America. Considering the presence or absence of animal reservoirs for Leishmania, two basic types of epidemiological cycles are noted: zoonotic (ZVL) or anthroponotic (AVL) [reviewed in [2]].AVL in India and Central Africa is caused by L. donovani and involves a severe parasitism of the blood and skin and an anthropophilic vector, making man the reservoir of the disease. In contrast, ZVL with dogs as reservoir hosts is usually associated with L. infantum and is found in the Americas, the Middle East, Central Asia, China and the Mediterranean. ZVL is considered a canid zoonosis in which sandflies become infected mostly by feeding on the skin of canids and humans are the final host of the parasites. Blood-parasitism in people with ZVL was at first considered not to occur [3] but has been shown recently [4,