Leishmaniasis is a parasitic disease caused by protozoan parasites belonging to the genus Leishmania and is transmitted by the bite of a species of sand fly. Two species of sand fly transmit Leishmania to humans: Lutzomyia in the New World and Phlebotomus in the Old World. Most forms of the disease are transmissible only from animals (zoonosis), but some can be spread between humans. Human infection is caused by about 21 of 30 species that infect mammals. The different species are morphologically indistinguishable, but they can be differentiated by isoenzyme analysis, DNA sequence analysis, or monoclonal antibodies.
The four main forms of leishmaniasis:
- Visceral leishmaniasis – the most serious form and potentially fatal if untreated.
- Cutaneous leishmaniasis – the most common form which causes a sore at the bite site, which heal in a few months to a year, leaving an unpleasant looking scar. This form can progress to any of the other three forms.
- Diffuse cutaneous leishmaniasis – this form produces widespread skin lesions which resemble leprosy and is particularly difficult to treat.
- Mucocutaneous leishmaniasis – commences with skin ulcers which spread causing tissue damage to (particularly) nose and mouth
Leishmaniasis can be transmitted in many tropical and sub-tropical countries, and is found in 88 countries containing 350 million people. The settings in which leishmaniasis is found range from rainforests in Central and South America to deserts in West Asia. It affects as many as 12 million people worldwide, with 2 million new cases each year. The visceral form of leishmaniasis has an estimated incidence of 500,000 new cases and 60,000 deaths each year. More than 90 percent of the world’s cases of visceral leishmaniasis are in India, Bangladesh, Nepal, Sudan, and Brazil. Leishmaniasis is found through much of the Americas from northern Argentina to southern Texas, but not in Uruguay or Chile, and has recently been shown to be spreading to North Texas. The disease is found across much of Asia, though not Southeast Asia, and the Middle East. Within Afghanistan, leishmaniasis occurs commonly in Kabul. Africa, in particular the East and North, is home to Leishamaniasis. The disease is spreading to Southern Europe but is not found in Oceania. Leishmaniasis is mostly a disease of the Developing World, and is rarely known in the developed world outside a small number of cases, mostly in instances where troops are stationed away from their home countries.
Signs and symptoms
- skin sores which erupt weeks to months after the person affected is bitten by sand flies
- damage to the spleen (one of the causes of a markedly enlarged spleen, which may become larger even than the liver.
- damage to the liver
Leishmaniasis is diagnosed in the hematology laboratory by direct visualization of the amastigotes (Leishman-Donovan bodies).
There are two common therapies containing antimony (known as pentavalent antimonials): meglumine antimoniate (Glucantime) and sodium stibogluconate (Pentostam). In many parts of the world, the parasite has become resistant to antimony and for visceral or mucocutaneous leishmaniasis, but the level of resistance varies according to species. Amphotericin is now the treatment of choice. Drug-resistant leishmaniasis may respond to immunotherapy (inoculation with parasite antigens plus an adjuvant) which aims to stimulate the body’s own immune system to kill the parasite. Several potential vaccines are being developed. Currently there are no vaccines in routine use.