ABSTRACT
More than a dozen identified and characterized species of the genus Leishmania cause diseases, ranging from simple self-healing cutaneous lesions to debilitating and lethal (if untreated) visceral leishmaniasis (VL) known as kala-azar (Table 1). Other less frequent forms are mucosal leishmaniasis (ML), a highly disfiguring disease of oral and nasal cavities, and diffuse cutaneous leishmaniasis (DCL), with hundreds of nodular lesions spread over the body. Self-limiting visceral infections with some Leishmania species (Leishmania infantum [1], L. donovani [2], and, possibly L. tropica [3]) may also occur. These asymptomatic individuals as well as cured cases would later develop disease if their immune responses are depressed by drugs or human immunodeficiency virus (HIV) infection, indicating nonsterile immunity following cure [4]. The persistence of parasites in resistant mouse strains long after the recovery of the initial lesion has been documented [5,6], and leishmaniasis recidivans (reappearance of new satellite lesions) around the original healed lesion is occasionally seen with L. tropica infection. In this respect, leishmaniasis is considered as an opportunistic infection [7]. All forms of leishmaniasis are naturally transmitted by the bites of female sandflies either from infected humans (anthroponotic leishmaniasis) or from infected animals (zoonotic). Generally, there is a good association between the organism and the type of disease it produces in humans (Table 1). However, L. tropica, usually the causative agent of anthroponotic cutaneous leishmaniasis (ACL), may cause VL as was seen in U.S. soldiers returning from the Desert Storm operation [3], and L. infantum, the causative agent of zoonotic VL, can cause CL [8]. Approximately 350 million people are believed to be at risk of infection and the annual incidence of new cases is about 2 million, mostly in children and young adults (1.5 million CL and the rest VL). The current estimated prevalence is 12 million, distributed in 88 countries [9]. These
figures do not include epidemics, which can claim the lives of tens of thousands of individuals, eliminate communities, and cause massive migration [10].
