onchocerciasis / river blindness

introduction

onchocerciasis is caused by the nematode (roundworm) parasite Onchocerca volvulus
it is the world's second-leading infectious cause of blindness affecting some 270,000 of the 18 million people infected by it
it is not the nematode, but its endosymbiont, Wolbachia pipientis, which is released once the nematode dies, that causes the severe inflammatory response that leaves many blind.
the parasite is transmitted to humans through the bite of a black fly of the genus Simulium.
the vast majority of infections occur in sub-Saharan Africa, although cases have also been reported in Yemen and isolated areas of Central and South America.
humans are the hosts in the life cycle of this nematode and thus it is not a zoonosis.
thus whole communities need to be treated to break the cycle.

skin involvement typically consists of intense itching, swelling, and inflammation resulting in papules, hyperpigmentation, and later hypopigmentation (“leopard skin” especially on the shins), then elephant skin as it becomes thickened
ocular involvement is initially a punctate keratitis which may resolve or become chronic sclerosing keratitis
uveitis, retinitis and optic neuritis may also occur.