Leishmania tropica

The first description of Leishmania tropica was done in 1903 by James Homer Wright, an American pathologist. In 1914, it was suggested that L. tropica should be divided into two subspecies, namely L. tropica minor and L. tropica major, based on the size of the parasites found in skin lesions. Later, these two subspecies turned out to be epidemiologically different and were correlated to different types of lesions. L. tropica minor causes dry nodular lesions in urban environments, while L. tropica major causes wet ulcerating lesions in rural regions. which is the naming that is still being used. == Biology ==

The parasite has an interesting biology since it is very heterogeneous biochemically, serologically, and genetically compared to other Leishmania species. The different strains have been shown to cause different patterns of pathogenicity and humoral immune responses in BALB/c mice models. Through simple division, they can multiply and proceed to infect other phagocytotic cells. Later, depending partly on the immunity of the host, the infection can become symptomatic and result in leishmaniasis. Sand flies become infected by ingesting phagocytes with Leishmania from a mammalian host. Then, in the sandfly stage, the process differs between Leishmania species. In the life cycle of L. tropica, it develops back into the promastigote stage inside the midgut of the sandfly vector and migrates to the proboscis of the sandfly, whereafter the life cycle can repeat itself. == Hosts and vectors ==

Humans are the main reservoir hosts of L. tropica. are a possible reservoir in Israel. Natural infection by L. tropica has also been demonstrated in domestic dogs, red foxes, golden jackals, gundis, and other species of wild rodents. The main sandfly vector for L. tropica is Phlebotomus sergenti. Other reported vector species are P. arabicus, P. guggisbergi, P. chabaudi, P. rossi, and P. saevus. == Clinical manifestations ==

L. tropica causes a broad spectrum of leishmaniasis forms in humans. Most common is a variant called dry-type cutaneous leishmaniasis. After an incubation period lasting more than 2 months, a small brownish nodular lesion will appear with a slowly extending plaque reaching a size of after 6 months. This will heal after about 1 year but leaves a scar. Other forms of the disease, which occur more rarely in humans, include visceral leishmaniasis, post-kala-azar dermal leishmaniasis (a variant of visceral leishmaniasis), viscerotropic leishmaniasis, and leishmaniasis recidivans (a variant of cutaneous leishmaniasis). Leishmaniasis recidivans This rare variant of cutaneous leishmaniasis is caused solely by L. tropica in the Old World and by L. braziliensis in the New World. It causes a slowly progressing lesion, usually on the face, and is characterized by the development of papules or nodules which form mostly around or in the site of primary healed lesions. Lesions of leishmaniasis recidivans stay many years and rarely respond to treatment, thus causing disfigurement and becoming destructive with the years. ==References==