Tse-tse fly is a vector for sleeping sickness that transmits the infective stage of which of the following parasite

The correct option is Trypanosoma gambiense.

Here is a step-by-step educational breakdown explaining why this is the correct answer:

1. Understanding the Disease and the Vector:
Sleeping sickness, also known as Human African Trypanosomiasis (HAT), is a parasitic disease native to sub-Saharan Africa. The disease is transmitted to humans and other animals through the bite of an infected tsetse fly (genus Glossina), which acts as the biological vector.

2. Identifying the Causative Parasite:
The causative agent of African sleeping sickness is a microscopic, single-celled protozoan parasite belonging to the genus Trypanosoma. Specifically, the subspecies $\mathrm{Trypanosoma} \mathrm{brucei} \mathrm{gambiense}$ (often referred to simply as Trypanosoma gambiense) is responsible for the chronic form of West and Central African sleeping sickness, representing over 95% of reported cases.

3. Analyzing the Incorrect Options:
Let us review the other organisms mentioned in the options to see why they do not match:
- Wuchereria bancrofti: This is a parasitic filarial nematode (roundworm) that causes lymphatic filariasis (commonly known as elephantiasis) and is transmitted primarily by mosquitoes, not tsetse flies.
- Leishmania donovani: This protozoan parasite causes visceral leishmaniasis (kala-azar) and is transmitted to humans by the bite of infected female phlebotomine sandflies.
- Plasmodium falciparum: This protozoan parasite is the causative agent of malaria (malignant tertian malaria) and is transmitted via the bite of infected female Anopheles mosquitoes.

Conclusion:
Thus, the tsetse fly specifically acts as a vector for the transmission of the parasite Trypanosoma gambiense, leading to sleeping sickness.