Option 1: Cholera is not caused by a protozoan. It is caused by the bacterium Vibrio cholerae, which is transmitted through contaminated water or food.

Option 2: Malaria is the correct answer. Malaria is caused by a protozoan parasite known as Plasmodium. The parasite is transmitted to humans through the bite of infected female Anopheles mosquitoes. Once inside the human body, Plasmodium multiplies in the liver and then infects red blood cells, leading to symptoms such as fever, chills, and fatigue.

Option 3: Tuberculosis is caused by the bacterium Mycobacterium tuberculosis, not a protozoan. It primarily affects the lungs but can also affect other parts of the body.

Option 4: Typhoid is caused by the bacterium Salmonella typhi, not a protozoan. It is usually transmitted through contaminated food or water and can lead to symptoms such as high fever, headache, and abdominal pain.

In conclusion, the correct answer to the question is option 2: Malaria.