Leishmania

A group of parasites causing a disease called leishmaniasis. For a fuller definition and more information, see Leishmania infection.

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A genus of digenetic, asexual, protozoan flagellates (family Trypanosomatidae) that occur as amastigotes in the macrophages of vertebrate hosts, and as promastigotes in invertebrate hosts and in cultures. Species are largely indistinguishable morphologically, but may be separated by clinical manifestations, geographic distribution and epidemiology, developmental patterns of promastigotes in their sandfly hosts, virulence testing of clones in vivo, the effect of test sera on growth in culture, cross-immunity tests, and serotyping with promastigote excreted factors; strains also can be distinguished by various biochemical analyses. Such procedures have identified all of the recognized groups and confirmed the separation of New World leishmaniasis agents into two species complexes, L. mexicana and L. braziliensis. [W. B. Leishman]

- L. aethiopica an African species of L. responsible for human cutaneous leishmaniasis in Ethiopia, with a reservoir of human infection in the rock hyraxes, Procavia capensis and Heterohyrax brucei, and in Kenya, with reservoirs in the tree hyrax, Dendrohyrax arboreus, and the giant rat, Cricetomys gambianus; vectors are the sandflies Phlebotomus longipes and P. pedifer. It causes a cutaneous leishmaniasis of three types: classical oriental sore, mucocutaneous leishmaniasis, and diffuse cutaneous leishmaniasis; ulceration is late or absent and healing takes one to three years.

- L. braziliensis a species that is the causal agent of mucocutaneous leishmaniasis, endemic in southern Mexico and Central and South America, and transmitted by various species of Lutzomyia (New World sandflies); forest rodents and other neotropical arboreal animals serve as reservoir hosts. L. braziliensis is currently divided into three clinically, epidemiologically, and biochemically distinct strains or subspecies: L. b. braziliensis, L. b. guyanensis, and L. b. panamensis.

- L. braziliensis braziliensis the type subspecies of L. braziliensis and the agent of mucocutaneous leishmaniasis. A natural reservoir of infection remains unknown, but the proven vector in Brazil is Lutzomyia (Psychodopygus) wellcomei; other sandflies may also transmit the infection.

- L. braziliensis guyanensis a subspecies within the L. braziliensis complex from Brazil and Guyana, and the cause of the cutaneous leishmaniasis condition locally known as “pian bois”; the reservoir host in Brazil is the sloth Choloepus hoffmani and the vector is the sandfly Lutzomyia umbratilis.

- L. braziliensis panamensis a subspecies of L. braziliensis found in Panama, Colombia, and neighboring regions; it causes ulcerating lesions of cutaneous leishmaniasis which do not heal spontaneously and often involve nearby lymphatic tissues, but nasopharyngeal involvement is rare. The sloth Choloepus hoffmani is the reservoir in Panama and Costa Rica; the sandfly Lutzomyia trapidoi has been proven to be a vector.

- L. donovani a species that is the causal agent of visceral leishmaniasis in Mediterranean and adjacent countries, the south central section of the former USSR, eastern India, northern China, Kenya, Ethiopia, and the Sudan; also found in Brazil, Argentina, Colombia, and Venezuela; in the Old World, it is transmitted by various species of Phlebotomus; New World vectors are species of Lutzomyia; dogs and other carnivores are known as reservoir hosts in some areas. The intracellular amastigote form multiplies in macrophages and produces a reticuloendothelial hyperplasia grossly affecting the spleen and liver, with other lymphoid tissues being involved as well, resulting in severe hepatosplenomegaly, which usually is fatal if untreated.

- L. donovani archibaldi L. donovani donovani.

- L. donovani chagasi a subspecies of L. found in South America, chiefly in Brazil, producing visceral leishmaniasis; infections have been found in domestic dogs and in foxes, though the primary reservoir host is unclear. The vector remains undiscovered, and the taxonomic status of this subspecies is uncertain.

- L. donovani donovani the type subspecies and agent of visceral leishmaniasis in Asia, Africa, and the Indian subcontinent; a few cases occur in the south central section of the former USSR, and in Iran, Iraq, and possibly Yemen; the dog and jackal are animal reservoirs. The form in Africa may be this subspecies, though the name L. donovani archibaldi is also used.

- L. donovani infantum a strain or subspecies of L. donovani that causes visceral leishmaniasis in young children in Mediterranean countries; the reservoir is the domestic dog.

- L. furunculosa former name for L. tropica.

- L. major a species responsible for zoonotic cutaneous leishmaniasis in a large area of the Mediterranean region and Asia Minor. The animal reservoirs are usually ground squirrels, such as Rhombomys opimus in the former USSR and elsewhere in south central Asia, and other rodents in northwest India, the Middle East, and northern Africa; proven sandfly vectors include Phlebotomus papatasi, P. duboscqi, and P. salehi. SYN: L. tropica major.

- L. mexicana the agent of many forms of cutaneous leishmaniasis, now considered a complex of several subspecies or possibly species, each with distinctive DNA and enzyme characteristics, distribution, and vector-reservoir host association, resulting in distinct manifestations of human leishmaniasis; reservoir hosts are extremely diverse and include a wide array of arboreal rodents as well as marsupials, primates, and small carnivores. Typical disease forms caused by this species are chiclero ulcer and diffuse cutaneous leishmaniasis, in contrast with mucocutaneous leishmaniasis, more characteristic of L. braziliensis infection. SYN: L. tropica mexicana.

- L. mexicana amazonensis a particularly widespread form of L. mexicana in the Amazon basin (Bolivia, Brazil, Colombia, Ecuador, and southern Venezuela), where it infects a variety of forest rodents, the reservoirs of human infection. The disease is rare in humans, but the single or multiple lesions, when induced, rarely heal spontaneously; the disseminated form is common, but nasopharyngeal involvement does not occur. The vector is the sandfly Lutzomyia flaviscutellata.

- L. mexicana garnhami a subspecies of L. mexicana, found in western Venezuela, causing single or multiple lesions in humans that heal spontaneously in about six months; the probable sandfly vector is Lutzomyia townsendi.

- L. mexicana mexicana a species described from Mexico, Guatemala, and Belize; agent of a form of New World cutaneous leishmaniasis called chiclero ulcer, associated with chicle gum and mahogany forest workers. The New World sandfly, Lutzomyia olmeca, is a proven vector of this subspecies.

- L. mexicana pifanoi a strain of L. mexicana accorded species status by those who consider it responsible for the diffuse or disseminated form of cutaneous leishmaniasis. It is responsible for this condition in Venezuela, where it was described, but it is now recognized that several species and subspecies of L. cause similar disseminated forms of leishmaniasis in widely separated regions (L. mexicana amazonensis, L. aethiopica); absence or suppression of the cell-mediated immune response in the host is also an important factor in induction of diffuse cutaneous leishmaniasis. SYN: L. pifanoi.

- L. mexicana venezuelensis a recently described subspecies of L. mexicana from Venezuela that causes indolent, nodular, single lesions of cutaneous leishmaniasis to develop, sometimes with curable disseminated cutaneous leishmaniasis; infection has also been found in equines.

- L. peruviana species of L. found infecting humans in the high Andean valleys of Peru and Bolivia; cause of a distinct form of New World cutaneous leishmaniasis called uta.

- L. pifanoi SYN: L. mexicana pifanoi.

- L. tropica species that is the causal agent of anthroponotic cutaneous leishmaniasis; formerly endemic throughout the Mediterranean basin, the Middle East, parts of the southern section of the area formerly known as the USSR and elsewhere in Asia, and also reported from western Africa; it is transmitted by Phlebotomus papatasi, P. sergenti, and related species of sandflies; small rodents such as various ground squirrels serve as reservoir hosts.

- L. tropica major SYN: L. major.

- L. tropica mexicana SYN: L. mexicana.

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leish·man·ia lēsh-'man-ē-ə, -'mān- n

1) cap a genus of kinetoplastid flagellate protozoans of the family Trypanosomatidae that are parasitic in the tissues of vertebrates, are transmitted by sand flies (genera Phlebotomus and Lutzomyia), occur parasitically as a minute ovoid or spherical nonflagellated body with a definite kinetoplast and usu. an intracellular axoneme, and include one (L. donovani) causing kala-azar and another (L. tropica) causing oriental sore

2) any protozoan of the genus Leishmania broadly any protozoan of the family Trypanosomatidae having the typical intracellular form of a leishmania

leish·man·ial -ē-əl adj

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n.

a genus of parasitic flagellate protozoans, several species of which cause disease in humans (see leishmaniasis). The parasite assumes a different form in each of its two hosts. In humans, especially in kala-azar patients, it is a small rounded structure, with no flagellum, called a Leishman-Donovan body, which is found within the cells of the lymphatic system, spleen, and bone marrow. In the insect carrier it is long and flagellated.

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Leish·ma·nia (lēsh-maґne-ə) [Sir William B. Leishman] 1. a genus of flagellate protozoa of the order Kinetoplastida, phylum Euglenozoa, comprising parasites of worldwide distribution; several species are pathogenic. The organisms have two morphologic stages in their life cycle: amastigote, found intracellularly in the vertebrate host; and promastigote, found in the digestive tract of the invertebrate host (i.e., phlebotomine sandfly) and in cultures. The genus is divided into two subgenera, Leishmania and Viannia, based on the location of development within the sandfly vector; species of the former are present in both the Old and New Worlds, while those of the latter are found only in the New World. The organisms have usually been assigned to complexes and species according to their geographic origin, clinical syndrome produced, and ecologic characteristics, or have been separated on the basis of association with visceral, cutaneous, or mucocutaneous leishmaniasis, but classification increasingly is based on phylogenetic relationships. 2. a subgenus of the genus Leishmania, comprising the species that develop in the midgut and foregut.