“Amoebiasis” or amoebic dysentery is caused by

The correct option is Entamoeba histolytica.

Step-by-step Explanation:

1. Understanding Amoebiasis:
Amoebiasis, also known as amoebic dysentery, is a gastrointestinal infection characterized by symptoms like abdominal pain, diarrhea, and bloody stools. It is primarily transmitted through the ingestion of food or water contaminated with the cysts of the causative organism.

2. Identifying the Causative Agent:
The infection is caused by a microscopic protozoan parasite called Entamoeba histolytica. The parasite colonizes the human large intestine, where it can invade the mucosal lining, leading to ulceration and dysentery.

3. Analyzing the Other Options:
- Trypanosoma histolytica is not a valid scientific name (Trypanosoma species typically cause diseases like sleeping sickness or Chagas disease).
- Entamoeba gingivalis is a related protozoan that lives in the human oral cavity and is generally non-pathogenic, associated primarily with periodontal disease rather than dysentery.
- Plasmodium vivax is the protozoan parasite responsible for causing malaria, not gastrointestinal infections.

Therefore, the parasite responsible for causing amoebiasis is indeed Entamoeba histolytica.