**Question:** Kallu is a 30-year-old man presenting with subcutaneous itchy nodules over the left iliac crest. On examination, the nodules are firm, non-tender, and mobile. Skin scraping reveals microfilariae and adults of a worm. Which of the following is the most likely diagnosis?

A. Filariasis
B. Lymphatic filariasis
C. Onchocerciasis
D. Loiasis

**Core Concept:** Filariasis is a group of parasitic diseases caused by filarial worms, specifically microfilariae and adults. These worms belong to the genera Wuchereria, Brugia, and Onchocerca. The three most common types of filariasis are lymphatic filariasis (caused by Wuchereria bancrofti), filariasis (caused by Brugia malayi and Brugia timori), and onchocerciasis (caused by Onchocerca volvulus).

**Why the Correct Answer is Right:** The correct answer is D. Loiasis, as it is caused by Loa loa filariae, which are responsible for the adult worms found in the skin nodules and microfilariae in the skin scraping. Loiasis is characterized by palpable microfilariae in the skin and subcutaneous tissues, similar to the patient's presentation.

**Why Other Options are Incorrect:**

A. Filariasis (Wuchereria bancrofti): This is the cause of lymphatic filariasis, which affects the lymphatic system, not the skin. The worms are found in the lymphatic vessels, not the skin nodules.

B. Filariasis (Brugia malayi and Brugia timori): These worms cause filariasis, affecting the lymphatic system, not the skin. The worms are found in the lymphatic vessels, not the skin nodules.

C. Onchocerciasis (Onchocerca volvulus): This is the cause of onchocerciasis, a condition affecting the skin, eyes, and muscles. The worms are found in the skin, not the subcutaneous nodules and skin scraping. Onchocerciasis presents differently and has different worms (Onchocerca volvulus) compared to Loiasis (Loa loa).

**Clinical Pearls:**

1. Loiasis is a skin filariasis caused by Loa loa filariae.
2. The microfilariae can be palpated in the skin and subcutaneous tissues, which is the hallmark feature of Loiasis.
3. Loiasis is endemic in West and Central Africa, whereas the other filariases (A, B, C) are endemic in Southeast Asia and South Asia.

**Correct Answer Explanation:**

The correct answer is D (Loiasis) because the clinical presentation matches the patient's symptoms: subcutaneous nodules and skin microfilariae. Additionally, Loiasis is endemic in West and Central Africa, which aligns with the