Leishmania

Life > Eukaryotes > Excavata > Euglenozoa > Kinetoplastea > Metakinetoplastina > Trypanosomatida

Parasites of mammals that are transmitted by sandflies (Psychodidae: Phlebotominae). There are almost 30 species, of which 21 are known to infect people, causing the disease symptoms collectively known as leishmaniasis. 

"With 21 species of human-infective parasites, numerous reservoir and vector species, in a wide range of topographically different foci, the ecology and epidemiology of the leishmaniases are extremely diverse - without doubt the most diverse of all the vector-borne diseases."  Lane (1993)

The symptoms of leishmaniasis are shown in four main forms:

• Cutaneous leishmaniasis (oriental sore). An ulcer forms at the site where a sandfly has bitten. The parasite is usually only found in the region of the ulcer but in some species, it also infects the lymphatic system, causing skin wounds along the lymphatic ducts. 
  • In the Old World this type of leishmaniasis is found mainly in arid regions: North Africa, Middle East to northwestern India and central Asia, East Africa, small parts of the Sahel and southern Africa. Main causative species are L. major, L. tropica and L. aethiopica
  • In the New World it is found mainly in forests from Mexico to northern Argentina. Main causative species are L. guyanensis, L. panamensis and L. mexicana.
• Mucocutaneous leishmaniasis (espundia). A disfiguring disease that invades and erodes the cartilaginous tissues of the nose and palate. The original bite by the sandfly can be on any part of the body where it causes a small wound that eventually heals. However, in about 5% of cases, the parasite spreads to the naso-pharyngeal region, sometimes a number of years after being bitten. Healing is never spontaneous and untreated patients can die from secondary infections. This type of leishmaniasis is caused by the species L. braziliensis and L. panamensis and is found in South America.  
• Diffuse cutaneous leishmaniasis. Characterised by widespread papules or nodules in the skin all over the body. Does not heal spontaneously and is difficult to treat. In Africa (Kenya, Ethiopia) it is caused mainly  by L. aethiopica and in Central America and northern South America it is caused mainly by L. amazonensis.
• Visceral leishmaniasis. The parasite invades the cells of the spleen, liver and bone-marrow, resulting in death if not treated.
  • In the Old World, it is found sporadically from the Mediterranean region through the Middle East and Central Asia to northern China, usually in rocky areas. In these regions is affects mainly children. It is also found in northeastern India, Bangladesh and Nepal where it affects mainly young adults living on the plains. The causative agents are L. infantum (the specific name referring to its tendency to affect children) and L. donovani. 
  • In the New World it is found throughout Central and South America, but it mainly occurs in northeastern Brazil. The causative agent is usually called L. chagasi but according to some authorities it is in fact L. infantum.

References

• Lane, R.P. 1993. Sandflies (Phlebotominae). In: Medical Insects and Arachnids (eds R.P. Lane and R.W. Crosskey). Chapman and Hall, London, pp. 78-119.

Text by Hamish Robertson