When the Anopheles mosquito takes a blood meal on another human, anticoagulant saliva is injected together with the sporozoites, which migrate to the liver, thereby beginning a new cycle. After 10-18 days, a form of the parasite called a sporozoite migrates to the mosquito’s salivary glands. When certain forms of blood stage parasites (gametocytes, which occur in male and female forms) are ingested during blood feeding by a female Anopheles mosquito, they mate in the gut of the mosquito and begin a cycle of growth and multiplication in the mosquito. The blood stage parasites are those that cause the symptoms of malaria.
In the blood, successive broods of parasites grow inside the red cells and destroy them, releasing daughter parasites (“merozoites”) that continue the cycle by invading other red cells. In humans, the parasites grow and multiply first in the liver cells and then in the red cells of the blood. The natural history of malaria involves cyclical infection of humans and female Anopheles mosquitoes.
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