(1) The sandflies inject the infective stage, metacyclic promastigotes, during blood meals. (2) Metacyclic promastigotes in the puncture wound are phagocytized by macrophages, and (3) transform into amastigotes. (4) Amastigotes multiply in infected cells and affect different tissues, depending in part on the host, and in part on which Leishmania species is involved. These differing tissue specificities cause the differing clinical manifestations of the various forms of leishmaniasis. (5,6) Sandflies become infected during blood meals on infected hosts when they ingest macrophages infected with amastigotes. (7) In the sandflys midgut, the parasites differentiate into promastigotes, (8) which multiply, differentiate into metacyclic promastigotes, and migrate to the proboscis. The genomes of three Leishmania species (L. major, L. infantum, and L. braziliensis) have been sequenced, and this has provided much information about the biology of the parasite. For example, in Leishmania, protein-coding genes are understood to be organized as large polycistronic units in a head-to-head or tail-to-tail manner; RNA polymerase II transcribes long polycistronic messages in the absence of defined RNA pol II promoters, and Leishmania has unique features with respect to the regulation of gene expression in response to changes in the environment. The new knowledge from these studies may help identify new targets for urgently needed drugs and aid the development of vaccines. Vector
Although most of the literature mentions only one genus transmitting Leishmania to humans (Lutzomyia) in the New World, a 2003 study by Galati suggested a new classification for New World sand flies, elevating several subgenera to the genus level.
About 200 million people in Asia, Africa, South and Central America, and southern Europe live in areas where the disease is common. The World Health Organization has obtained discounts on some medications to treat the disease. It is classified as a neglected tropical disease. The disease may occur in a number of other animals, including dogs and rodents. Signs and symptoms
The symptoms of leishmaniasis are skin sores which erupt weeks to months after the person is bitten by infected sand flies. Leishmaniasis may be divided into the following types:
Cutaneous leishmaniasis is the most common form, which causes an open sore at the bite sites, which heals in a few months to a year and half, leaving an unpleasant-looking scar. Diffuse cutaneous leishmaniasis produces widespread skin lesions which resemble leprosy, and may not heal on its own. Mucocutaneous leishmaniasis causes both skin and mucosal ulcers with damage primarily of the nose and mouth. Visceral leishmaniasis or kala-azar (black fever) is the most serious form, and is generally fatal if untreated. Other consequences, which can occur a few months to years after infection, include fever, damage to the spleen and liver, and anemia.Leishmaniasis is considered one of the classic causes of a markedly enlarged (and therefore palpable) spleen; the organ, which is not normally felt during examination of the abdomen, may even become larger than the liver in severe cases. Cause
Leishmaniasis is transmitted by the bite of infected female phlebotomine sandflies which can transmit the protozoa Leishmania.