Visceral leishmaniasis can cause large-scale and tenacious epidemics, with high case–fatality rates. Epidemics occur frequently in regions which are difficult to access, such as Libo Kemkem, Ethiopia (2005–06), Wajir, Kenya (2008), and Upper Nile, Southern Sudan (2009). Malnutrition is a well-known risk factor, and the epidemics flourish under conditions of famine, complex emergencies and mass population movements.
In Sudan a major epidemic of visceral leishmaniasis occurred from 1984 to 1994. As this was the first epidemic in the area, the population was highly susceptible. Some studies have estimated that the disease caused 100 000 deaths in a population of around 300 000 in the western upper Nile area of the country. In some villages, more than half of the population died from the disease.
In 1997, a new epidemic caused the number of confirmed cases of visceral leishmaniasis in Sudan to increase by 400% over the previous year. Treatment centres were overwhelmed and stocks of first-line drugs were depleted. The migration of seasonal workers and large population movements caused by civil unrest carried the epidemic into Eritrea and Ethiopia.
Brazil has also experienced a sharp increase in the number of cases of visceral leishmaniasis since 1999. Previously, rural epidemics were seen in ten-year cycles. Now, the disease is also appearing in urban areas. Waves of drought, lack of available farmland, and famine have led to a large migration of the population from rural areas to the peripheral suburbs of large cities, creating densely populated settlements with minimal infrastructure and sanitation. In these settlements, the newly introduced parasite finds a vast number of non-immune hosts, who are often malnourished and thus more vulnerable. Children under the age of 15 years are the most severely affected group. Dogs habitually kept in the domestic environment are the principal animal reservoir for the infection. Visceral leishmaniasis is also progressing rapidly in the north of Argentina and the areas bordering Brazil and Paraguay. In Paraguay itself, urban transmission has been seen in the capital Asunción.
Epidemics of cutaneous leishmaniasis are of particular concern in Afghanistan, where decades of war and civil unrest have created conditions that favour the spread of the disease and make its control especially difficult. The disease flared up in 2002, with an estimated 100 000 cases in Kabul. Today there are around 35 000 cases a year in the city. Because of their low resistance to the disease, returning refugees and other displaced persons in Kabul are at higher risk of infection. Outbreaks of cutaneous leishmaniasis are occurring in different parts of the world, and have been well reported in the southern provinces of Sing and Beluchistan in Pakistan since 2004, in Ban, Islamic Republic of Iran after the devastating earthquake in 2003, and in the Sudanese refugee camps of Treguine and Koukou, Chad in 2007.