Final answer:
Giardia lamblia is a protozoan that causes giardiasis, entering the body via fecal-oral transmission, typically found in contaminated water or food, and known for its cyst stage that can survive harsh environmental conditions.
Step-by-step explanation:
Giardia lamblia is a flagellate protozoan responsible for the illness known as giardiasis. The parasite is known to enter the body through a fecal-oral route, commonly through the consumption of contaminated food or water. Giardia attaches itself to the lining of the host's small intestine with a large adhesive disk, impeding nutrient absorption and often causing symptoms such as diarrhea, abdominal pain, and fever. The cysts of Giardia are known to convert to trophozoites in the small intestine, not the large intestine as might be incorrectly presumed. These cysts are incredibly resilient and can survive in cold temperatures and even resist chlorination, requiring that municipal water be filtered to remove them. Individuals who drink untreated water from natural sources, like rivers, lakes, or streams, particularly backpackers and campers, are at a higher risk of contracting giardiasis. This parasite is also commonly transmitted between individuals in settings such as daycare centers or through contact with infected animals.