LEISHMANIASIS

LEISHMANIASIS

Etiology
Several species of Leishmania are pathogenic for man: L. donovani causes visceral leishmaniasis (Kala-azar, black disease, dumdum fever); L. tropica (L. t. major, L. t. minor and L. ethiopica) cause cutaneous leishmaniasis (oriental sore, Delhi ulcer, Aleppo, Delhi or Baghdad boil); and L. braziliensis (also, L. mexicana and L. peruviana) are etiologic agents of mucocutaneous leishmaniasis (espundia, Uta, chiclero ulcer).

Epidemiology
Leishmaniasis is prevalent world wide: ranging from south east Asia, Indo-Pakistan, Mediterranean, north and central Africa, and south and central America.

Morphology
Amastigote (leishmanial form) is oval and measures 2-5 microns by 1 - 3 microns (figure 10A-D), whereas the leptomonad measures 14 - 20 microns by 1.5 - 4 microns, a similar size to trypanosomes
Life cycle
The organism is transmitted by the bite of several species of blood-feeding sand flies (Phlebotomus) which carry the promastigote in the anterior gut and pharynx. The parasites gain access to mononuclear phagocytes where they transform into amastigotes and divide until the infected cell ruptures. The released organisms infect other cells. The sandfly acquires the organisms during the blood meal; the amastigotes transform into flagellate promastigotes and multiply in the gut until the anterior gut and pharynx are packed. Dogs and rodents are common reservoirs (figure 11F).

Symptoms

Visceral leishmaniasis (kala-azar, dumdum fever): L. donovani organisms in visceral leishmaniasis are rapidly eliminated from the site of infection, hence there is rarely a local lesion, although minute papules have been described in children. They are localized and multiply in the mononuclear phagocytic cells of spleen, liver, lymph nodes, bone marrow, intestinal mucosa and other organs. One to four months after infection, there is occurrence of fever, with a daily rise to 102-104 degrees F, accompanied by chills and sweating. The spleen and liver progressively become enlarged (figure 11B, C and E). With progression of the diseases, skin develops hyperpigmented granulomatous areas (kala-azar means black disease). Chronic disease renders patients susceptible to other infections. Untreated disease results in death.

Cutaneous leishmaniasis (Oriental sore, Delhi ulcer, Baghdad boil): In cutaneous leishmaniasis, the organism (L. tropica) multiplies locally, producing of a papule, 1-2 weeks (or as long as 1-2 months) after the bite. The papule gradually grows to form a relatively painless ulcer. The center of the ulcer encrusts while satellite papules develop at the periphery. The ulcer heals in 2-10 months, even if untreated but leaves a disfiguring scar (figure 12). The disease may disseminate in the case of depressed immune function.

Mucocutaneous leishmaniasis (espundia, Uta, chiclero): The initial symptoms of mucocutaneous leishmaniasis are the same as those of cutaneous leishmaniasis, except that in this disease the organism can metastasize and the lesions spread to mucoid (oral, pharyngeal and nasal) tissues and lead to their destruction and hence sever deformity (figure 12E). The organisms responsible are L. braziliensis, L. mexicana and L. peruviana.

Pathology
Pathogenesis of leishmaniasis is due to an immune reaction to the organism, particularly cell mediated immunity. Laboratory examination reveals a marked leukopenia with relative monocytosis and lymphocytosis, anemia and thrombocytopenia. IgM and IgG levels are extremely elevated due to both specific antibodies and polyclonal activation.

Diagnosis
Diagnosis is based on a history of exposure to sandfies, symptoms and isolation of the organisms from the lesion aspirate or biopsy, by direct examination or culture. A skin test (delayed hypersensitivity: Montenegro test) and detection of anti-leishmanial antibodies by immuno-fluorescence are indicative of exposure.

Treatment and Control
Sodium stibogluconate (Pentostam) is the drug of choice. Pentamidine isethionate is used as an alternative. Control measures involve vector control and avoidance. Immunization has not been effective.