Leishmaniasis is caused by single-cell parasites of the genus Leishmania. More than 10 different Leishmania species can cause human disease. The two main clinical manifestations of leishmaniasis are:

• Visceral leishmaniasis, caused by infections with Leishmania donovani, L. infantum or L. chagasi.
• Cutaneous leishmaniasis, caused by infections with either L. major or L. tropica (in the Old World) or with the New World species: L. amazonensis, L. mexicana, L. braziliensis, L. colombiensis, L. guyanensis, L. panamensis and L. peruviana

Human leishmaniasis
Visceral leishmaniasis, affecting an estimated 500.000 – 1.000.000 people each year, is a deadly disease if left untreated. The parasites colonise the internal organs, in particular the spleen, liver, bone marrow and lymph nodes. Cutaneous leishmaniasis affects more than 1.500.000 people per year. In the case of cutaneous leishmaniasis, the parasite is confined to the skin where it causes one or more slow-healing sores, and in some species also lesions along the draining lymphatic vessels, so-called nodular lymphangitis. As severe type of cutaneous leishmaniasis is muco-cutaneous leishmaniasis, whereby the infection spreads to the mucosal membranes, especially those of mouth and nose, where it may cause extensive damage.

Veterinary leishmaniasis
Leishmaniasis is not only a human health problem. A large variety of animals, including dogs, opossums and rats, can also become infected with Leishmania parasites and may suffer from the disease. Leishmaniasis in dogs is important in countries around the Mediterranean Sea and in many countries in Latin America. However, the disease is also more and more frequently reported as an import disease in northern Europe.