Emergencies preparedness, response

WHO Report on Global Surveillance of Epidemic-prone Infectious Diseases - Leishmaniasis

Background of the disease

Leishmaniasis is a parasitic infection transmitted by the bite of an infected female sandfly whose hosts are animals, such as dogs or rodents, or human beings. Leishmaniasis is a highly focal disease with widely scattered foci. The parasite may survive for decades in asymptomatic infected people, who are of great importance for the transmission since they can spread visceral leishmaniasis indirectly through the sandflies. The parasites can also be transmitted directly from person to person through the sharing of infected needles which is often the case with the Leishmania/HIV co-infection. The disease has four main forms, depending on the parasite species and the cellular immune system of the patient:

Leishmaniasis has a long history. Designs on pre-Colombian pottery and the existence of thousand-year old sculls with evidence of leishmaniasis prove that the disease has been present in the Americas for a long time. It has also been present in Africa and India since at least the mid-eighteenth century (1). Today, an estimated 12 million cases of leishmaniasis exist worldwide with an estimated number of 1.5 -2 million new cases occurring annually; 1 - 1.5 million cases of cutaneous leishmaniasis and 500 000 cases of visceral leishmaniasis (2).

The geographical distribution of leishmaniasis is restricted to tropical and temperate regions, the living area of the sandfly. The leishmaniases are considered to be endemic in 88 countries (16 developed countries and 72 developing countries) on four continents. 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. Because of an accumulation of risk factors such as civil unrest, disruption of health systems, malnutrition, underlying diseases and due to absence of diagnostic facilities and first line drugs at local level, the mortality rate was very high and 40 000 people were reported to have died due to the disease. Studies indicate that in some villages up to half of the population succumbed to the disease (3); one study suggests that during this ten-year period visceral leishmaniasis claimed 100 000 lives in a population of around 300 000 in Western Upper Nile State (4).

There is reason to believe that the number of cases of leishmaniasis is increasing (5). 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. According to agencies operating clinics in the city of Kabul, Afghanistan, an estimated 270 000 cases of cutaneous leishmaniasis occurred in 1996 among the less than 2 million inhabitants of the city (6). Kabul is a city where a lot of movement of people from rural to urban areas takes place. Another risk factor is the movement of susceptible populations into endemic areas, including large-scale migration of populations for economic reasons such as the development of agro-industrial projects.

Interaction between surveillance and response

Early case detection and treatment are the most important control measures for leishmaniasis. In anthroponotic leishmaniasis in which humans are the only reservoir, early detection and treatment reduces morbidity and mortality. Treatment reduces or eliminates parasite loads, and this in turn reduces transmission. Thus surveillance and control are directly linked. The main limitations to treatment are high cost and the relatively long treatment period. In severe situations such as epidemics and highly endemic areas vector control is also used. It consists of house spraying or the use of insecticide-impregnated bed nets.

For zoonotic visceral leishmaniasis, which is usually fatal if left untreated, priority is also given to the detection and treatment of human cases. Other control measures include large-scale screening and testing of dogs, the main reservoir, spraying of houses and animal shelters, and individual protection. Environmental management measures such as destroying breeding and resting sites of the vector have been recommenced for zoonotic cutaneous leishmaniasis control.

With the use of insecticide-impregnated bed nets and new tests for serological diagnosis, progress has been made in the prevention and control of leishmaniasis infection. However, better methods are still needed such as more affordable drugs with shorter treatment periods.

Leishmania/HIV co-infection

Leishmaniasis is one of the opportunistic infections that attack HIV-infected individuals, most of the co-infection involves the visceral form of leishmaniasis (7). Recently more notice has been taken of Leishmania/HIV co-infection.

Cutaneous leishmaniasis Cutaneous leishmaniasis produces skin lesions mainly on the face, arms and legs. Although this form is often self-healing, it can create serious disability and permanent scars. After recovery or successful treatment, cutaneous leishmaniasis induces immunity to re-infection by the species of Leishmania that caused the disease.
Diffuse cutaneous leishmaniasis
Diffuse cutaneous leishmaniasis is difficult to treat due to disseminated lesions that resemble leprosy and do not heal spontaneously. This form especially is related to a defective immune system and it is often characterized by relapses after treatment.
Mucocutaneous leishmaniasis Mucocutaneous leishmaniasis, also called 'espundia' in South America, causes disfiguring lesions to the face; it destroys the mucous membranes of the nose, mouth and throat. Reconstructive surgery of deformities is an important part of therapy.
Visceral leishmaniasis
Visceral leishmaniasis, also known as 'kala azar', is characterized by irregular fever, weight loss, swelling of the liver and spleen and anaemia. It is the most severe form of Leishmaniasis, and is usually fatal if left untreated. 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.

Map 10.1 shows the global distribution of reported cases of Leishmania/HIV co-infection and the distribution of leishmaniasis cases. Up to 1999, 31 countries have reported Leishmania/HIV co-infection. There is concern that Leishmania/HIV co-infection may increase the transmission of leishmaniasis, particularly the visceral form. The overlap in the geographical areas with high risk of both HIV and leishmaniasis is increasing, with the spread of leishmaniasis (typically a rural disease) into urban areas and the increased spread of HIV into rural areas. Leishmaniasis patients are highly susceptible to HIV infection and in HIV- infected patients, leishmaniasis accelerates the onset of AIDS by cumulative immuno-suppression and by stimulation of the replication of the virus. It also may change asymptomatic Leishmania infections into symptomatic ones. In addition, since visceral leishmaniasis can be spread intravenously, sharing of needles by intravenous drug users is a direct way of spreading leishmaniasis.

Map 10.1 Global distribution of reported cases of leishmaniasis and Leishmania/HIV co-infection, 1990-1998

Map 10.1 Global distribution of reported cases of leishmaniasis and Leishmania/HIV co-infection, 1990-1998

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