This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infection, Subject name: Medicine
"River blindness" is caused by: 
Select and explain. 
A. Onchocera-Volvulus, B. Schistoma haematobium, C. Fasciola hepatica, D. Opisthorchis-viverrini
A: Onchocera-Volvulus
Answer: A: Onchocera-Volvulus 
Explanation: (onchocera - volvulus) Ref: 1327-HI7th)ONCHOCERCIASIS: (River blindness) is caused by the filarial nematode O valvulus* Pruritis and rash are the most frequent manifestations of onchocerciasis* Visual impairment is the most serious complication of onchocerciasis. The most common early finding is conjunctivitis with photophobia "Snow flake" opacies is frequent in younger patients.* Enlarged nodes may hand down in response to gravity ^hanging grom ") sometimes predisposing to inguinal and femoral hernias* Mazzotti test is a provocative technique* IVERMECTIN is the treatment of choice for onchocerciasis