Transmission

Malaria is an infection caused by single-celled parasites that enter the blood through the bite of a female Anopheles mosquito. All Plasmodium species spend one portion of their life cycle inside humans and another part inside mosquitoes.

When a female Anopheles mosquito bites a person infected with malaria, it ingests blood containing malaria parasites. The parasites must spend about two weeks in the mosquito to undergo further life cycle changes before they can infect humans again. When the mosquito feeds again, the parasites are injected into a new person.

During the human part of their life cycle, Plasmodium parasites infect and multiply inside red blood cells and/or liver cells. Infected blood cells eventually burst, sending waves of new Plasmodium parasites into the bloodstream and triggering malaria symptoms. Also, in patients with P. vivax or P. ovale infections, some Plasmodium parasites remain dormant inside the liver, waiting to trigger malaria relapses months or years later.

Because Plasmodium parasites are carried in the blood, malaria can also be spread through contaminated blood transfusions, transplanted organs and shared drug needles. In pregnant women, malaria infection can pass through the bloodstream to the developing foetus causing low birth weight or foetal death (most common in P. falciparum infection). Malaria infection in pregnant women may be more severe than in women who are not pregnant. Because of these increased risks all pregnant women who are living in or travelling to a malaria-risk area should consult a doctor and take prescription drugs to avoid contracting malaria.