Pathogenesis (development of disease)
Malaria is caused by the various species of the genus Plasmodium (Plasmodium falciparum; Plasmodium vivax; Plasmodium ovale; Plasmodium malariae; Plasmodium knowlesi; Plasmodium semiovale). These have a two-part development cycle, one part of which (sexual cycle) occurs in the vector mosquito (Anopheles) and another in humans.
If the pathogen has been transmitted to humans via the bite of the Anopheles mosquito, asexual multiplication of the plasmodia occurs in two consecutive multiplication cycles. They invade liver cells and develop there into tissue schizonts (= tissue schizogony; pre-erythrocytic phase). Some of these schizonts (stage in the developmental cycle of Sporozoa) mature into merozoites, which periodically enter the blood and attach themselves to erythrocytes (red blood cells). If the infected erythrocytes disintegrate (hemolysis), merozoites are released again, which infect further erythrocytes (= blood schizogony). Some form sexual forms macro-/microgametocytes. The remaining portion of schizonts remain in a dormant phase as hypnozoites and can be induced to mature after stimulation.
Exclusively blood schizonts are responsible for disease symptoms.
Etiology (causes)
Behavioral causes
- Failure to provide adequate protection from mosquito bites in malaria-endemic areas (Malaria occurs at a sustained, appreciable rate in circa 100 countries; malaria-endemic areas are: Africa and Asia)
Other causes
- Airport malaria – infection on the plane or at the airport by imported mosquitoes.
- Baggage malaria – infection by mosquitoes from airline luggage.
- Very rarely, transmission can occur through blood bags or shared injection systems; needle stick injuries can also occur as transmission
- Diaplacental infection from mother to unborn child may occur
