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These are parasites of the skin found in endothelial cells of the capillaries of the infected site, nearby lymph nodes, within large mononuclear cells, in neutrophilic leukocytes, and free in the serum exuding from the ulcerative site. Metastasis to other site or invasion of the viscera is rare.
Pathogenesis
In neutrophilic leukocytes, phagocytosis is usually successful, but in macrophages the introduced parasites round up to form amastigote and multiply. In the early stage, the lesion is characterized by the proliferation of macrophages that contain numerous amastigotes. There is a variable infiltration of lymphocytes and plasma cell. The overlying epithelium shows acanthosis and hyperkeratosis, which is usually followed by necrosis and ulceration.
Epidemiology
Cutaneous leishmaniasis produced by L.tropica complex is present in many parts of Asia, Africa, Mediterranean Europe and the southern region of the former Soviet Union. The urban cutaneous leishmaniasis is thought to be an anthroponosis while the rural cutaneous leishmaniasis is zoonosis with human infections occurring only sporadically. The reservoir hosts in L. major are rodents. L.aethopica is endemic in Ethiopia and Kenya. The disease is a zoonosis with rock and tree hyraxes serving as reservoir hosts. The vector for the old world cutaneous leishmaniasis is the Phlebotomus sand fly.
Clinical features
The first sign, a red papule, appears at the site of the fly’s bite. This lesion becomes irritated, with intense itching, and begins to enlarge and ulcerate. Gradually the ulcer becomes hard and crusted and exudes a thin, serous material. At this stage, secondary bacterial infection may complicate the disease. In the case of the Ethiopian cutaneous leishmaniasis, there are similar developments of lesions, but they may also give rise to diffuse cutaneous leishmaniasis (DCL) in patients who produce little or no cell mediated immunity against the parasite. This leads to the formation of disfiguring nodules over the surface of the body.
Immunity
Both humoral and cell mediated immunity (CMI) are involved
Treatment
The drug of choice is sodium stibogluconate, with an alternative treatment of applying heat directly to the lesion. Treatment of L.aethopica remains to be a problem as there is no safe and effective drug.
Prevention
Prompt treatment and eradication of ulcers – Control of sand flies and reservoir hosts
