**Question:** In which stage of filariasis are microfilaria seen in peripheral blood:

A. Acute phase
B. Subacute phase
C. Chronic phase
D. None of the above

**Core Concept:**
Filarial infections are caused by filarial worms, primarily transmitted through the bite of an infected mosquito. The life cycle of filarial worms involves several stages, including the development of microfilariae (larval forms) in the peripheral blood. In the context of the question, we are specifically looking at the stage where microfilariae are visible in the bloodstream.

**Why the Correct Answer is Right:**
Microfilariae are visible in the peripheral blood during the subacute phase of filariasis. This stage follows the acute phase, where the initial immune response to the filarial infection causes the worms to migrate to lymph nodes, where they are destroyed. In the subacute phase, the worms reproduce, leading to the presence of microfilariae in the blood.

**Why Each Wrong Option is Incorrect:**
A. Acute phase: Microfilariae are not typically seen in the peripheral blood during this stage, as the worms are migrating to lymph nodes for destruction by the immune system.
B. Chronic phase: Microfilariae are present in the blood during the chronic phase, but this is not the correct answer because the correct answer is the subacute phase.
C. None of the above: Inaccurate as the subacute phase is the correct answer, where microfilariae are present in the blood.

**Clinical Pearl:**
Understanding the life cycle and stages of filarial infections is essential for diagnosing and managing patients with filarial diseases. The presence of microfilariae in the peripheral blood is a key diagnostic clue, especially when combined with clinical symptoms and signs of filariasis.