What is leishmaniasis?
Human leishmaniasis is not a disease, but a group of diseases. The leishmaniases are caused by infection with protozoan parasites from the Leishmania genus. Most species of Leishmania are zoonotic (affecting animals as well as humans), with the exception of the visceral form of L. tropica and L. donovani, where no animal host/reservoir has been found to date. It is believed that worldwide 12 million people are affected by leishmaniasis; this figure includes cases with overt disease and those with no apparent symptoms. Of the 1.5-2 million new cases of leishmaniasis estimated to occur annually, only 600 000 are officially declared. The geographical distribution of leishmaniasis is limited by the distribution of the sandfly, its susceptibility to cold climates, its tendency to take blood from humans or animals only and its capacity to support the internal development of specific species of Leishmania. Since 1993, regions that are Leishmania-endemic have expanded significantly, accompanied by a sharp increase in the number of recorded cases of the disease. The geographic spread is due to factors related to development and mass migration. These include massive rural-urban migration and agro-industrial projects that bring non-immune urban dwellers into endemic rural areas, or warfare areas. Man-made projects with environmental impact, like dams, irrigation systems and wells, as well as deforestation, also contribute to the spread of leishmaniasis. AIDS and other immunosuppressive conditions increase the risk of Leishmania-infected people developing visceral illness. In certain areas of the world the risk of co-infection with HIV is rising due to epidemiological changes.