Kala-azar, also known as visceral leishmaniasis, is transmitted by (c) Anopheles fly. This disease is caused by the protozoan parasite Leishmania donovani, primarily transmitted to humans through the bite of infected female sandflies of the genus Phlebotomus (Old World) or Lutzomyia (New World). These sandflies typically thrive in rural areas with poor sanitation and are most active during dusk and dawn. When an infected sandfly bites a human, it injects the parasite into the bloodstream, leading to the development of kala-azar. Effective control measures, such as vector control and treatment of infected individuals, are essential to prevent the spread of this disease.