Diseases are caused by various agents. Which one of the following agent causes Kala-azar?

The correct option is C

Protozoa

Protozoa are one of the three main classes of parasites that cause diseases in humans. They are single-celled organism, and can only be seen under a microscope. Kalaazar disease is caused by the Leishmania parasite. These parasites are found mainly in southern Europe, the tropics and subtropics. The most common form of this disease being spread is through the bite of a sand fly, which carries the parasite. So pathogen is Leishmania and vector is Sandfly. Kala-azar is also called as Leishmaniasis.