Which form of Giardia lamblia is responsible for infection in humans?

Giardia lamblia, a flagellated microorganism, exists in two primary forms: cysts and trophozoites. The cyst form is notably the infective stage for humans. When a person ingests contaminated water or food containing these cysts, they can survive in the harsh environment of the gastrointestinal tract. Inside the host, the cysts excyst to release trophozoites, which can cause intestinal symptoms.

Cysts are highly resilient and can remain viable in the environment for long periods, making them a common route of transmission. In contrast, the trophozoite form is the active, motile stage that reproduces within the intestines, but it is not responsible for initiating infection.

Understanding the lifecycle of Giardia lamblia is crucial for epidemiology and disease prevention, as it emphasizes the importance of water hygiene and sanitation to prevent cyst transmission.