Leishmaniasis: Middle East and North Africa Research and Development Priorities
Figure 2
Although at least 20 Leishmania spp. infect humans worldwide, the primary epidemiologically relevant species in the MENA region are L. major, L. tropica, L. infantum, and L. donovani, transmitted by approximately 25 different Phlebotomus spp. Etiological agents of visceral leishmaniasis (VL) in MENA include L. donovani, L. infantum, and occasionally L. tropica. Cutaneous leishmaniasis (CL) caused by L. major, L. tropica, and L. infantum differ slightly in lesion presentation depending on the species. As with vector species, a variety of animal hosts have been implicated as reservoirs in the transmission of zoonotic leishmaniasis, including rodents, hyraxes, and canids. For CL caused by L. major, the primary cycle is zoonotic between P. papatasi (shown) and Psammoys (shown) and Meriones rodents. Although hyraxes have been implicated as a reservoir host for L. tropica, transmission is thought to be primarily anthroponotic as is the VL agent, L. donovani. Mediterranean VL caused by L. infantum is typically zoonotic where candids are the primary reservoir and man is an accidental host; however, anthroponitic cycles also have been characterized. Regardless of species or clinical manifestation, all Leishmania species infecting humans are transmitted by the bite of an infected sand fly. During a blood meal, metacyclic promastigotes are released by the sand fly and enter the skin of the vertebrate host. Leishmania parasites infect cells of the myeloid lineage, including neutrophils, followed by macrophages and dendritic cells (shown). These parasites reside within a phagolysosome where they differentiate into a dividing, aflagellated amasitogotes. Sand flies take up parasites when feeding on an infected host. Infected host cells are lysed and amastigotes differentiate into flagellated procyclic promastigotes that attach to the midgut of the sand fly vector. Subsequent development and migration towards the anterior end of the sand fly completes the cycle. Photo Credits: P. papatasi courtesy of Tim Gathany, Center for Disease Control Photo Services; Psammomys obesus from http://commons.wikimedia.org/wiki/File:Psammomys_obesus_01.jpg; rock hyrax from http://www.marietta.edu/~biol/biomes/biome_main.htm.
