The disease and its epidemiology

The vector

The leishmaniases are caused by 20 species pathogenic for humans belonging to the genus Leishmania, a protozoa transmitted by the bite of a tiny 2 to 3 millimetre-long insect vector, the phlebotomine sandfly.

Phlebotomine Sandfly

Of 500 known phlebotomine species, only some 30 of them have been positively identified as vectors of the disease. Only the female sandfly transmits the protozoa, infecting itself with the Leishmania parasites contained in the blood it sucks from its human or mammalian host in order to obtain the protein necessary to develop its eggs.

During a period of 4 to 25 days, the parasite continues its development inside the sandfly where it undergoes a major transformation.

When the now infectious female sandfly feeds on a fresh source of blood, its painful sting inoculates its new victim with the parasite, and the transmission cycle is completed.

Phlebotomine sandfly

The insect vector of leishmaniasis, the phlebotomine sandfly, is found throughout the world's inter-tropical and temperate regions.

The female sandfly lays its eggs in the burrows of certain rodents, in the bark of old trees, in ruined buildings, in cracks in house walls, in animal shelters and in household rubbish, as it is in such environments that the larvae will find the organic matter, heat and humidity which are necessary for their development.

In its search for blood (usually in the evening and at night), the female sandfly covers a radius of a few to several hundred metres around its habitat.

Various forms of leishmaniasis

Leishmaniasis currently threatens 350 million men, women and children in 88 countries around the world. The leishmaniases are parasitic diseases with a wide range of clinical symptoms:
cutaneous, mucocutaneous and visceral.

Cutaneous forms

Dr Desjeux P. WHO/HQ

Cutaneous forms of the disease normally produce skin ulcers on the exposed parts of the body such as the face, arms and legs.

The disease can produce a large number of lesions - sometimes up to 200 - causing serious disability and invariably leaving the patient permanently scarred, a stigma which can cause serious social prejudice.

Mucocutaneous forms

Credit: Dr Desjeux P.

In mucocutaneous forms of leishmaniasis, lesions can lead to partial or total destruction of the mucous membranes of the nose, mouth and throat cavities and surrounding tissues.

These disabling and degrading forms of leishmaniasis can result in victims being humiliated and cast out from society.

Visceral forms

Dr Desjeux P. WHO/HQ

Visceral leishmaniasis - also known as kala azar - is characterized by irregular bouts of fever, substantial weight loss, swelling of the spleen and liver, and anaemia (occasionally serious). If left untreated, the fatality rate in developing countries can be as high as 100% within 2 years.