African sleeping sickness or Gambiense fever is caused by

The correct option is Trypanosoma.

African sleeping sickness, also known as Human African Trypanosomiasis (HAT) or Gambiense fever, is a vector-borne parasitic disease.
It is caused by microscopic parasites of the species Trypanosoma brucei. Specifically, the subspecies Trypanosoma brucei gambiense is responsible for the chronic form of the disease (Gambiense fever) found in West and Central Africa.

The parasite is transmitted to humans by the bite of an infected tsetse fly (genus Glossina), which acquires the parasite from infected humans or animals.

Let's look at why the other options are incorrect:
- Leishmania: Causes leishmaniasis, a disease spread by the bite of infected sandflies.
- Entamoeba: Specifically Entamoeba histolytica, causes amoebiasis or amoebic dysentery.
- Trichomonas: Specifically Trichomonas vaginalis, causes trichomoniasis, a sexually transmitted infection.