The incubation period can be months or years and, unlike the cutaneous forms of leishmaniasis, it involves the internal organs. After treatment and recovery, patients may develop chronic cutaneous leishmaniasis that requires long and expensive treatment. Leishmaniasis has a long history. The geographical distribution of leishmaniasis is restricted to tropical and temperate regions, the living area of the sandfly. Ninty percent of cases with cutaneous forms of leishmaniasis occur in Afghanistan, Algeria, Brazil, Iran, Peru, Saudi Arabia and Syria, while ninety per cent of visceral leishmaniasis cases are found in Bangladesh, Brazil, India, Nepal and Sudan.
Visceral leishmaniasis can cause large-scale epidemics with high case fatality.
For example, Western Upper Nile State in South Sudan experienced a major outbreak of visceral leishmaniasis between 1984 and 1994. This was the first epidemic in this area and therefore people were very susceptible to the disease. This is partly due to man-made environmental changes which increase human exposure to the sandfly vector. Extracting timber, mining, building dams, widening areas under cultivation, new irrigation schemes, road construction in primary forests such as the Amazon, widespread migration from rural to urban areas and fast urbanization worldwide are among the main causes for an increased exposure to the sandfly. Kabul is a city where a lot of movement of people from rural to urban areas takes place.