## **Core Concept**
Onchocerca volvulus is a parasitic worm that causes onchocerciasis, also known as river blindness. The treatment of onchocerciasis involves targeting the adult worms and microfilariae. The ideal drug should be effective against both.

## **Why the Correct Answer is Right**
Ivermectin is the correct answer because it is highly effective against the microfilariae of Onchocerca volvulus, which are the cause of the disease's symptoms. Ivermectin works by **increasing the release of chloride ions** into the parasite, leading to hyperpolarization, paralysis, and death of the microfilariae. A single dose of ivermectin can significantly reduce the microfilarial load and alleviate symptoms.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Albendazole is primarily used for treating infections caused by nematodes and cestodes but is not the first choice for onchocerciasis.
- **Option B:** Mebendazole is another antiparasitic drug effective against a variety of helminths but is not the preferred treatment for onchocerciasis.
- **Option D:** Diethylcarbamazine is actually used to treat filariasis but is not the drug of choice for onchocerciasis and can even exacerbate the condition by causing severe reactions.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **ivermectin is the drug of choice for onchocerciasis**, and mass treatment programs have been implemented in endemic areas to control the disease. It's also important to note that while ivermectin is effective, it does not kill the adult worms but rather targets the microfilariae.

## **Correct Answer:** C. Ivermectin