Electron microscopical studies on onchocerciasis. I. Mesenchyme reaction in untreated onchocercal dermatitis and ultrastructure of the microfilariae.

Skin biopsies of 22 untreated Liberian patients suffering from onchocercal dermatitis were studied by electron microscopy. The microfilariae tend to accumulate in the upper dermis, without eliciting a cellular reaction. Occasionally macrophages or mast cells are found in the neighbourhood of the microfilariae. The most conspicuous changes concern the presence of perivascular infiltrates, comprised of lymphocytes and macrophages, with a varying admixture of plasma cells. Only exceptionally the macrophages show an increase in number and size of their lysosomes and pseudopodia as well as prominent strands of ergastoplasm indicating an activation. The endothelial walls of the dermal vessels are swollen. The amount of mast cells in the upper dermis is increased. Ultrastructural features of the microfilariae are described, especially the cuticle, muscles, central undifferentiated cells and cephalic region. When comparing these findings with the literature on the fine structural morphology of the Latinamerican form, no differences can be found.