Leishmania

Texte anglais à traduire :
It is spread through sandflies of the genus Phlebotomus in the Old World, and of the genus Lutzomyia in the New World. They primary hosts is a vertebrate; Leishmania commonly infects hyraxes, canids, rodents, and humans. Leishmania currently affects 12 million people in 88 countries.

Leishmania cells have two morphological forms: promastigote (with an anterior flagellum) in the insect host, and amastigote (without flagella) in the vertebrate host. Infections are regarded as cutaneous, mucocutaneous, or visceral:

• Cutaneous (localized and diffuse) infections appear as obvious skin reactions. The most common is the Oriental Sore (caused by Old World species L. major, L. tropica, and L. aethiopica). In the New World, the most common culprits are L. mexicana and L. (Viannia) braziliensis. Cutaneous infections are most common in Afghanistan, Brésil, Iran, Pérou, Saudi Arabia and Syria.

• Mucocutaneous (espundia) infections will start off as a reaction at the bite, and can go metastasis into the mucous membrane and become fatal. Mucocutaneous infections are most common in Bolivia, Brazil and Peru.

• Visceral infections are often recognized by fever, weight loss, swelling of the liver and spleen, and anemia. They are known by many local names, of which the most common is probably Kala azar , and are caused exclusively by species of the L. donovani complex (L. donovani, L. infantum syn. L. chagasi). Visceral infections are most common in Bangladesh, Brazil, India, Nepal and Sudan.

An important aspect of the Leishmania protozoan is its glyconjugate layer of liphosphoglycan (LPG). This is held together with a phosphoinosite membrane anchor, and has a tripartite structure consisting of a lipid domain, a neutral hexasaccharide, and a phosphrorylated galactose-mannose, with a termination in a neutral cap. Not only do the little unfriendlies not develop post-phlebotomus digestion but, it is thought to be essential to oxidative bursts, thus allowing passage for infection. Chararacteristics of digestion include an endosome fusing with a lysosome, releasing acid hydrolases which degrade DNA, RNA, proteins and carbohydrates.

Treatments of the disease generally involve a solution containing antimoine, which is toxic. A solution which breaks down the LPG is also a form of treatment being looked at. Those who feel they are infected should seek immediate attention. Transmission is mainly through the bite of sand flies but also through needle-sharing by drugs users. Most at risk are humans infected with HIV, canines and rodents.

The origins of Leishmania are a well thought out subject. Theories vary. One proposes an African orgin, with migration to the Americas. Another migration from the Americas to the Old World about 15My ago, accross the Bering Strait land bridge. Another proposes a palaearctic origin. Such migrations would entail migration of vector and reservoir or successive adaptations along the way. A more recent migration is that of L. infantum from Mediterranean countries to Latin America (there named L. chagasi), since European colonization of the New World, where the parasites picked up its current New World vectors in their respective ecologies. This is the cause of the epidemics now evident. One recent New World epidemic concerns foxhounds in the USA.