Leishmaniasis is a group of clinical syndromes caused by the protozoan belonging to the genera Leishmania. The clinical spectrum of disease depends on the species causing the infection and includes subclinical infection, self-limited cutaneous and debilitating mucocutaneous disease, severe disseminated disease, and fatal visceral disease. Each condition has a relatively specific geographic distribution, biology, ecology, and natural mammalian reservoir, and its own vector. In nature, Leishmania can cause infection in a wide range of vertebrate hosts and is particularly common in canids, rodents, and primates, including humans.
PATHOGENESIS AND EPIDEMIOLOGY
The genus Leishmania belongs to the order Kinetoplastida and to the family Trypanosomatidae. More than 20 species of Leishmania affecting humans have been identified and are grouped according to their biochemical and genetic characteristics. They have been classified based on biological, clinical, and epidemiological features as belonging to three major clinical disease groups: (1) cutaneous leishmaniasis (CL), (2) mucocutaneous leishmaniasis (MCL), and (3) visceral leishmaniasis (VL) (Table 346-1).
TABLE 346-1LEISHMANIA SPECIES ASSOCIATED WITH DIFFERENT DISEASE PATTERNS ||Download (.pdf) TABLE 346-1LEISHMANIA SPECIES ASSOCIATED WITH DIFFERENT DISEASE PATTERNS
|Clinical Syndromes ||Type of Infection ||Leishmania Species |
|Cutaneous leishmaniasis (CL) ||Old World ||LL mexicana, LL amazonensis, LL venezuelensis, LV braziliensis, LV peruviana, LV panamensis, LV guayanensis |
|New World ||L tropica, L aethiopica, L major |
|Mucocutaneous leishmaniasis (MCL) ||Old World ||L aethiopica |
|New World ||LV braziliensis, LV panamensis, LV guayanensis |
|Visceral leishmaniasis (VL) ||Old World ||L donovani, L infantum |
|New World ||LL chagasi, LL amazonensis |
These single-celled parasites have a complex digenetic life cycle requiring a susceptible vertebrate host and a permissive vector to allow their transmission. They live within the phagocytes of the reticulo-endothelial system of mammals and in the intestinal tract of phlebotomine sandflies. Mammalian Leishmania species are present worldwide and are distributed mainly in tropical and subtropical areas of the Old (Europe, Africa, Asia) and the New Worlds (the Americas). In the Old World, the transmission is mainly peridomestic in the semiarid regions. In contrast, in the New World, it is more sylvatic with some species also exhibiting peridomestic transmission. Leishmania are obligate intracellular parasites in the vertebrate hosts that live only in the amastigote stage. Morphologically, the species that infect humans are indistinguishable by light microscopy and at the ultrastructural levels. Molecular typing is being recognized as a useful tool for clinical diagnosis, especially in areas where different species coexist. The Old World species of Leishmania are found to induce self-limiting disease while the New World species that may affect mucosal surfaces require more aggressive therapy. The main reservoirs of this protozoan are canids (eg, domestic dogs, foxes, jackals, wolves) and rodents.
The female sandfly is the only vector that is known to transmit leishmaniasis. In the Old World the genus Phlebotomus is responsible, while in the New World it is the genus ...