This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: parasitology, Subject name: Microbiology
River blindness is caused by - 
Select and explain. 
A. Onchocerca, B. Loa loa, C. Ascaria, D. B. Malayi
A: Onchocerca
Answer: A: Onchocerca 
Explanation: pathogenesis and clinical features The infective larvae deposited in the skin by the bite of the vector develop at the site to adult worms .Adult worms are seen singly, in pairs , or in tangled masses in the subcutaneous tissues ocular manifestations range from photophobia to gradual blurring of vision , progressing to total blindness. Ref : panikers textbook of medical parasitology 8th edition page 222