**Core Concept**
River blindness, also known as onchocerciasis, is a parasitic disease caused by the bite of an infected blackfly. It is characterized by severe itching, skin lesions, and vision loss due to inflammation of the eye.

**Why the Correct Answer is Right**
The disease is caused by the parasite *Onchocerca volvulus*, a filarial worm that is transmitted to humans through the bite of an infected blackfly. The parasite releases microfilariae into the bloodstream, which are then ingested by the blackfly. When the blackfly bites an individual, it deposits the microfilariae into the skin, leading to the characteristic symptoms of river blindness. The microfilariae cause a severe inflammatory response in the eye, leading to vision loss.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because river blindness is not caused by a viral infection, but rather by a parasitic worm.
**Option B:** This is incorrect because leprosy is caused by *Mycobacterium leprae*, a bacterium, and not a parasitic worm.
**Option C:** This is incorrect because Chikungunya is a viral infection caused by the Chikungunya virus, not a parasitic worm.

**Clinical Pearl / High-Yield Fact**
River blindness is a major public health problem in sub-Saharan Africa, and it is estimated that over 18 million people are at risk of infection. The disease can be prevented through the use of ivermectin, a medication that kills the microfilariae and reduces the severity of symptoms.

**Correct Answer:** C. Chikungunya