## **Core Concept**
The question describes a case of a 30-year-old man presenting with subcutaneous itchy nodules containing microfilariae and adult worms. This clinical presentation is suggestive of a parasitic infection known as **loiasis** or African eye worm, caused by the filarial parasite *Loa loa*.

## **Why the Correct Answer is Right**
The correct answer, *Loa loa*, is the causative agent of loiasis. This infection is characterized by the presence of **subcutaneous nodules** or "Calabar swellings" which are often itchy, firm, non-tender, and mobile. The skin scrapings from these nodules can contain both **microfilariae** and **adult worms**. *Loa loa* is transmitted by the bite of a deer fly (*Chrysops* species). The microfilariae develop into adult worms in the human host, which can then cause the characteristic subcutaneous nodules.

## **Why Each Wrong Option is Incorrect**
- **Option A:** *Wuchereria bancrofti* causes lymphatic filariasis, leading to conditions like elephantiasis, and does not typically present with subcutaneous nodules containing adult worms.
- **Option B:** *Brugia malayi* is another causative agent of lymphatic filariasis, similar to *Wuchereria bancrofti*, and does not cause the described clinical presentation.
- **Option D:** *Onchocerca volvulus* causes onchocerciasis or river blindness, characterized by skin nodules (onchocercomata) but the microfilariae are usually found in the skin or eye, not adult worms in skin scrapings.

## **Clinical Pearl / High-Yield Fact**
A key clinical feature of loiasis is the **migration of adult worms** through the subconjunctival tissue of the eye or through the skin, which can be visually observed. This unique feature, along with the presence of itchy subcutaneous nodules, helps in the clinical diagnosis of loiasis.

## **Correct Answer:** . Loa loa