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

## **Why the Correct Answer is Right**
Ivermectin is the correct answer because it is highly effective against the microfilariae of Onchocerca volvulus, reducing their numbers rapidly and preventing further transmission. It works by increasing the release of chloride ions into the parasite's muscle cells, leading to paralysis and death. Ivermectin is considered the drug of choice for onchocerciasis due to its efficacy, safety profile, and convenience of administration.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Albendazole is primarily used for treating infections caused by nematodes and cestodes, but it is not the first choice for onchocerciasis. It is used in combination with ivermectin for the treatment of lymphatic filariasis but not as a standalone treatment 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 used in the treatment of filariasis but is not the drug of choice for onchocerciasis. In fact, it can cause severe adverse reactions in patients with onchocerciasis.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while ivermectin is effective against the microfilariae of Onchocerca volvulus, it does not kill the adult worms efficiently. The adult worms can live for up to 15 years, and repeated treatments may be necessary to control the disease. Ivermectin is given annually for several years to control transmission.

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