He says forty-two percent of the Earth's population live in areas where malaria-transmitting mosquitoes exist. All of these people are at risk of being infected with malaria. He says the sad thing is that the majority of people who are killed by malaria are children. This is because their immune systems are not strong enough to fight the infection. Malaria is caused by a parasite called Plasmodium. The organism is injected into people through the bite of infected mosquitoes.