Which organism is primarily responsible for causing giardiasis?

Giardiasis is primarily caused by the protozoan parasite Giardia lamblia, also known as Giardia intestinalis. This organism is commonly found in contaminated water sources and is transmitted through the fecal-oral route. Infections can occur after ingesting cysts from contaminated water, food, or surfaces, leading to gastrointestinal symptoms such as diarrhea, abdominal cramps, and bloating.

Giardia lamblia has a distinctive pear shape and flagella that aid in its motility, which allows it to effectively colonize the intestinal tract and evade the host's immune system. The life cycle of Giardia includes both cyst and trophozoite stages, with the cyst form being highly resistant to environmental conditions and disinfection measures, thereby contributing to its transmission.

Understanding the characteristics and lifecycle of Giardia lamblia is crucial for diagnosing and treating giardiasis, making it the primary organism associated with this infection.