Magnitude of the problem

For many years, the public health impact of the leishmaniases has been grossly underestimated, mainly due to lack of awareness of its serious impact on health. Over the last 10 years, endemic regions have been spreading further and there has been a sharp increase in the number of recorded cases of the disease. As declaration is compulsory in only 32 of the 88 countries affected by leishmaniasis, a substantial number of cases are never recorded. In fact, 2 million new cases (1.5 million for CL and 500 000 for VL) are considered to occur annually, with an estimated 12 million people presently infected worldwide.

Under-reporting is substantial - only around 600 000 infections are officially reported each year. As with many diseases of poverty that cause high morbidity but low mortality, the true burden of leishmaniasis remains largely invisible, partly because those most affected live in remote areas, partly because the social stigma associated with the deformities and disfiguring scars caused by this disease keeps patients hidden. Leishmaniasis-related disabilities impose a great social burden, especially for women, and impair economic productivity. On several occasions, epidemics have significantly delayed the implementation of development projects. Leishmaniasis has thus become a disease which impedes soicoeconomic development.

Since 1993, the geographical distribution of leishmaniasis has expanded significantly, with a concomitant sharp increase in the number of cases. Visceral leishmaniasis can cause large-scale and tenacious epidemics with high case-fatality rates. Malnutrition is a well-known risk factor in the development of this form, and epidemics flourish under conditions of famine, complex emergencies and mass population movements. In Sudan, for example, a major decade-long epidemic of visceral leishmaniasis occurred from 1984 to 1994. As this was the first epidemic in the area, populations were highly susceptible. Some studies estimate 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 succumbed to the disease.

In 1997, the number of confirmed cases of visceral leishmaniasis in Sudan exploded, showing a 400% increase 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 Eritea and Ethiopia, where WHO announced similar emergencies in 1998.

Brazil has also experienced a sharp increase in the number of cases of visceral leishmaniasis since 1999. In this country, which has historically experienced rural epidemics in ten-year cycles, the disease is appearing in an urban form while the rural form persists. Waves of drought, lack of available farm land, and famine have led to a large migration of the population from rural areas to the peripheral suburbs of large cities, creating densley populated settlements with minimal infrastructure and sanitation. In these settlements, the newly-introduced parasite encounters a vast number of non-immune hosts who are often malnourished and thus at even greater risk. Dogs habitually kept in the domestic environment are the principal animal reservoir, and children under the age of 15 years are the most severely affected age group.

Though far less lethal, epidemics of the cutaneous form are of particular concern in Afghanistan, where decades of war and civil unrest have created conditions favouring spread of this disease and making its control especially difficult. The disease flared up in 2002, with an estimated 100 000 cases in Kabul. The situation is particularly explosive. Because of their lower levels of resistance to the disease, returning refugees and other displaced persons in Kabul are at higher risk of infection. International staff working in Afghanistan also face a substantially higher risk. WHO, together with the government of Afghanistan and several international NGOs, has taken emergency action to contain the epidemic.