Which organism is responsible for causing the disease known as giardiasis?

Giardiasis is a gastrointestinal infection caused by the protozoan parasite Giardia lamblia, which is also known as Giardia intestinalis. This organism is transmitted through contaminated water or food, or through person-to-person contact, particularly in settings with poor sanitation. Once ingested, Giardia lamblia attaches to the intestinal wall and multiplies, leading to symptoms such as diarrhea, abdominal cramps, and nausea.

The key characteristics of Giardia lamblia include its distinctive pear shape and the presence of flagella, which allow it to move in its environment. Its cyst form is resilient and can survive in the environment, making it a common cause of waterborne outbreaks.

While the other organisms listed are associated with different diseases—Entamoeba histolytica causes amoebic dysentery, Trichomonas vaginalis is known for causing trichomoniasis, and Necator americanus is a hookworm that causes anemia and other related issues—they are not responsible for giardiasis. Therefore, recognizing Giardia lamblia as the causative agent of giardiasis is essential for understanding this specific parasitic infection and its public health implications.