Plasmodium falciparum is the causative agent of the most severe form of malaria. It is distributed throughout the tropics. Explain why malaria is restricted to the tropics?

Plasmodium falciparum is a digenic protozoan and completes its life cycle in man and mosquito (female Anopheles). It causes malaria in humans. Malaria spreads when an infected mosquito bites man. Temperature of above 20°C is favourable for the growth of Plasmodium falciparum. The average temperature range in tropics is about 18 to 25 °C. Mosquitoes breed in these warm conditions. It thrives in areas with stagnant water. Hence, malaria is restricted to the tropics.