Histopathological and ultrastructural studies on human cutaneous leishmaniasis

Leishmania, a genus of intracellular protozoan parasites of macrophages, is the etiologic agent of cutaneous and visceral disease in man. In our study, localized cutaneous infections with leishmania were studied by light and transmission electron microscopy in 16 patients at phases ranging from onset to a progressive disease. In early infections, epidermal changes could be detected as deep hemorrhagic ulcer characterized by focal massive necrosis of the epidermal layers. Spongiotic vesicles in the epidermis were prominent containing the amastigotes. The dermal changes appeared in the form of diffuse inflammatory infiltrate predominantly composed of macrophages, epithelioid cells, lymphocytes, mast cells, and few plasma cells and eosinophils. Macrophages laden with the parasites were seen dissociating the striated muscle and the collagen bundles which showed degenerative and necrotic changes. In late stages of the disease, multiple granulomas formed predominantly of macrophages containing promastigotes and amastigotes, giant cells, epithelioid cells, and some mast cells were seen in the dermis. Some macrophages appeared vacuolated and loaded with the parasite. The dermal vasculature showed congestion, swelling of the endothelial cells, and fibrinoid necrosis of the wall. Some congested blood vessels demonstrated margination and diapedesis of inflammatory cells. By transmission electron microscopy, intact and degenerated amastigotes were seen phagocytosed inside the macrophagal parasitophorus vacuoles. Erythrophagocytosis and the reaction of other inflammatory cellular components were also described. These results clarified the lesions of leishmania invasion into the skin of the affected patients and its defensive mechanism. Moreover, the host macrophagal–parasite relationship was shown on ultrastructural level.