Laboratory research into the pathogenesis of ocular onchocerciasis

Despite its importance as a cause of blindness, there is still much to be learned about the way in which onchocerciasis damages ocular tissues. Much of the difficulty encountered in investigating the problem is due to the lack of an adequate laboratory model amenable to study outside the endemic areas of O. volvulus infection. An attempt has been made to reproduce the ocular effects of O. volvulus in humans by infecting rabbits and guinea-pigs and bovine (O. gutturosa) and equine (O. cervicalis) strains of Onchocerca. The subconjunctival inoculation of rabbits with microfilariae of O. volvulus can produce a keratitis comparable to that seen in the naturally occurring disease and there is evidence that the intensity of the inflammatory response can be modified by pre-immunization. Injecting microfilariae into the posterior segment is equally able to produce choroido-retinal lesions, but evidence that immunological mechanisms are involved is less obvious.