A child presented with one sided leg and scrotal swelling with hydrocoele and ocular lesions. Which parasite is responsible: March 2013

Ans. B i.e. Onchocerca volvulus Onchocerca volvulus It is a nematode that causes onchocerciasis or "river blindness" mostly in Africa. Long-term corneal inflammation, or keratitis, leads to thickening of the corneal stroma which ultimately leads to blindness. Humans are the only definitive host for 0. volvulus. The intermediate host or vector is the black fly (Simulium). 0. volvulus, along with most filarial nematodes, share an endosymbiotic relationship with the bacterium Wolbachia. In the absence of Wolbachia, larval development of the 0. volvulus is disrupted or ceased.