Forest and savanna onchocerciasis: comparative morphometric histopathology of skin lesions

A comparative study was made of skin biopsies from onchocerciasis patients living in the forest and in the savanna of West Africa. The lesions and their pathogenesis were similar in the two series of patients. An inflammatory reaction around the extra-lymphatic microfilariae was observed. But the localization of the microfilariae was slightly different: the mean distances between the microfilariae and the border of the basement membrane of the epidermis was approximately 115 microns in the forest and 138 microns in the savanna. Statistical analysis showed that the forest microfilariae were in the superficial parts of the dermis when the densities were low and in deep parts of the dermis when the densities were high. In the savanna, the phenomenon, although less clearly defined was reverse. The two situations were inverted when the density of microfilariae reached approximately 51 microfilariae per calibrated snip, which was seldom the case. Therefore, the most cases, microfilariae appeared to have been more superficial in the forest than the savanna.