Common Tropical Diseases Malaria Malaria is caused by a parasite called Plasmodium, which is transmitted via the bites of infected mosquitoes. In the human body, the parasites multiply in the liver, and then infect red blood cells. Kalaazar An infectious disease caused by an intracellular flagellate protozoan Leishmania donovani, common in rural parts of the tropical and subtropical countries of the world. The disease, also known as visceral leishmaniasis, is characterized by lesions of the reticulo-endothelial system, especially the liver and spleen, and is often fatal. Children are more susceptible to this disease. Kala-azar is transmitted to man by the bite of the infected female Phlebotomus sandfly. The incubation period is generally 2 to 6 months Chikungunya Chikungunya is a mosquito-borne viral disease first described during an outbreak in southern Tanzania in 1952. It is an alphavirus of the family Togaviridae. The name 'chikungunya' derives from a root verb in the Kimakonde language, meaning "to become contorted" and describes the stooped appearance of sufferers with joint pain. Dengue Dengue fever is a virus-based disease spread by mosquitoes.   Dengue fever is caused by one of four different but related viruses. It is spread by the bite of mosquitoes, most commonly the mosquito Aedes aegypti, which is found in tropic and subtropic regions.