## **Core Concept**
The question presents a case of a 30-year-old man, Kalu, with subcutaneous itchy nodules over the left iliac crest. The key findings include firm, nontender, and mobile nodules, with skin scrapings containing microfilariae and adult worms. This clinical presentation is suggestive of a parasitic infection, specifically one that causes subcutaneous filariasis.

## **Why the Correct Answer is Right**
The correct answer, **D. Onchocerca volvulus**, is right because Onchocerca volvulus is a parasitic worm that causes onchocerciasis, also known as river blindness. A key feature of onchocerciasis is the formation of subcutaneous nodules (onchocercomata) that contain adult worms. These nodules are typically firm, nontender, and mobile. The skin lesions and the presence of microfilariae and adult worms in skin scrapings are diagnostic of onchocerciasis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** *Wuchereria bancrofti* is incorrect because it primarily causes lymphatic filariasis, characterized by lymphedema and elephantiasis, not subcutaneous nodules.
- **Option B:** *Brugia malayi* is incorrect for similar reasons as Wuchereria bancrofti; it causes lymphatic filariasis and is not associated with subcutaneous nodules.
- **Option C:** *Loa loa* is incorrect because, while Loa loa does cause a form of filariasis with skin and eye manifestations (loiasis), the typical presentation includes the "African eye worm" and not usually subcutaneous nodules with both microfilariae and adult worms in skin scrapings.

## **Clinical Pearl / High-Yield Fact**
A memorable point for exams is that onchocerciasis (caused by Onchocerca volvulus) is associated with subcutaneous nodules containing adult worms and microfilariae, and it is also a cause of severe dermatitis and visual impairment, including blindness. A classic clinical correlation is the use of the term "hanging groin" to describe the skin changes.

## **Correct Answer: D. Onchocerca volvulus**