**Question:** Drug of choice in the treatment of onchocerciasis is

A. Albendazole
B. Ivermectin
C. Praziquantel
D. Pyrantel

**Core Concept:** Onchocerciasis is a parasitic disease caused by the filarial worm, Onchocerca volvulus. It predominantly affects the skin and eyes, leading to severe morbidity. The primary treatment option for onchocerciasis is a single dose of an appropriate antiparasitic drug.

**Why the Correct Answer is Right:**
B. Ivermectin is the correct answer due to its high efficacy against Onchocerca volvulus. Ivermectin belongs to the macrocyclic lactone class of drugs, which have potent antiparasitic activity. It acts by enhancing the neurotransmitter gamma-aminobutyric acid (GABA) in the parasites, causing overstimulation and paralysis leading to the death of the parasite.

**Why Each Wrong Option is Incorrect:**
A. Albendazole is a benzimidazole drug primarily effective against nematodes, particularly roundworms. It is not as effective against Onchocerca volvulus and is not the first choice for onchocerciasis treatment.

C. Praziquantel is primarily effective against cestodes (tapeworms) and not cestodes (roundworms). It is not the appropriate choice for treating onchocerciasis.

D. Pyrantel is a benzimidazole drug primarily effective against roundworms, particularly filarial worms. It is not the recommended treatment for onchocerciasis due to its limited efficacy against Onchocerca volvulus.

**Clinical Pearl:**
Ivermectin is a valuable tool in the management of onchocerciasis as it effectively targets the specific parasite, leading to a successful treatment outcome. In endemic areas, ivermectin mass drug administration (MDA) programs have been implemented to control and eliminate onchocerciasis through regular treatment of affected individuals.

**Correct Answer Explanation:**
Onchocerciasis, also known as river blindness, is a parasitic infection caused by the filarial worm Onchocerca volvulus. The disease primarily affects the skin and eyes, leading to severe morbidity and even mortality.

**Explanation of Onchocerciasis Pathophysiology:**
Onchocerca volvulus is transmitted through the bite of an infected blackfly (Stenopelmatinae family). After being bitten by an infected blackfly, the larvae migrate to the skin and then penetrate the host's skin, where they develop into adult worms that produce millions of microfilariae. These microfilariae then migrate to the skin, where they can cause severe dermal inflammation and skin pathology, as well as ocular lesions leading to blindness.

**Why Ivermectin is the Best Choice:**
Ivermectin is a macrocyclic lactone drug that has emerged as a valuable tool in the management of on