Mosquito transmitting malaria, illustration. A female mosquito is using its proboscis (mouthpart) to pierce the skin. Mosquitoes infected with Plasmodium parasites (lower left), the cause of malaria, can transmit the disease to humans when they bite them. The sporozoite (immature form) stage of the parasite is transmitted by the mosquito. It subsequently infects liver cells where it matures into the merozoite form and is released. When the parasites leave the red blood cells they rupture them. Symptoms of malaria include fever, headache and muscle pains.