ASCP Parasitology Practice Exam 2026 - Free Parasitology Practice Questions and Study Guide

The infective form of microsporidia is the resistant spore. Microsporidia are obligate intracellular parasites that are commonly found in a variety of hosts, including mammals, birds, and fish. The spores are unique because they have a tough outer wall that protects them from environmental stresses and allows them to remain viable for extended periods outside a host.

When the resistant spore enters a new host, it germinates and releases a polar filament that injects the infective spore's contents into the host's cells. This mechanism is crucial for the parasite's ability to establish an infection within the host's tissues. The lifecycle and survival of microsporidia rely heavily on this spore stage, not only for transmission between hosts but also for their resilience in harsh conditions.

The other forms mentioned do not apply to microsporidia. They do not have a free-living trophozoite stage, nor do they form cysts or larval stages in their lifecycle. Instead, their lifecycle is predominantly characterized by the formation of these resistant spores, which are essential for their transmission and survival. Consequently, the identification of the resistant spore as the infective form highlights the unique biology of microsporidia and their mode of infection.