Fundus lesions in the rabbit eye following inoculation of onchocerca volvulus microfilariae into the posterior segment. II. Pathology.

The injection of living microfilariae of Onchocerca volvulus into the vitreous or immediately beneath the retina of rabbits gave rise to a variable degree of choroiditis. Uveal inflammation was most marked in eyes inoculated directly into the retina and subretinal tissue. The choroiditis was characterised by lymphocytic, plasma cell and eosinophil infiltration and was associated in many instances with degeneration of the overlying retina and pigment epithelium. In the eyes of animals killed more than 40 days after inoculation with microfilariae the leucocytic infiltration was usually mild or even absent, and the predominant finding was circumscribed atrophy and degeneration of the retina. It is concluded that the pathogenesis of the lesions in posterior segment onchocerciasis is basically inflammatory with, possibly, a direct toxic action of the microfilariae on the retina.