Malaria, computer illustration. Malaria is a disease transmitted to humans by the bite of a female mosquito infected with Plasmodium parasites. The sporozoites (immature form, rod-shaped) infect liver cells where they mature into merozoites and are released into the bloodstream. The merozoites infect red blood cells and multiply. When the parasites leave the red blood cells they rupture them. Symptoms of malaria include fever, headache and muscle pains.