Subcutaneous nodules and skin lesions caused by several Onchocerca spp. in African cattle

Abstract

Subcutaneous nodules and skin biopsy specimens obtained from the umbilical area of 6 onchocercal Bos indicus were collected in Cameroon and subjected to a histological examination. The nodules containing Onchocerca ochengi and Onchocerca dukei showed the same structure as Onchocerca volvulus nodules in man ; they consisted of inflammatory pseudo-cysts often containing a female filaria. These pseudo-cysts were classified as “young”, “active” and “old” depending on the inflammatory cellular component of their walls. The nodules were surrounded by a connective tissue capsule criss-crossed by vessels containing sections of microfilariae and morula in the vascular lumen. The skin, infected with microfilariae of these two species, of 0. gutturosa and 0. armillata, showed various dermatitis lesions with fibrosis, similar to those observed in patients with onchocerciasis. In most cases, inflammatory infiltrates surrounded the lymphatic capillaries along the blood vessels, giving rise to lymphangitis. The presence of microfilariae inside the granulomatous tissue demonstrates that microfilariae were deposited directly into the cystic lumen. Only the microfilariae which escaped the inflammatory reaction were able to penetrate the lymphatic vessels. They could then migrate into the lymphatic system and reach the superficial layer of the dermis. Bovine nodular onchocercomata represent an interesting model for human onchocerciasis.