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Malaria is caused by protozoa of the genus Plasmodium and is spread to humans by mosquitoes. The history of malaria shows that it was difficult to determine the disease's mode of transmission. When some cultures reviewed the facts available to them, they concluded that malaria was caused by bad air without realizing that the same swamps that created foul-smelling air also were excellent breeding grounds for mosquitoes. In 1880, the parasite was identified in an infected patient's blood.
There are several stages in the life cycle of Plasmodium, including sporozoites, merozoites, and gametocytes. The bite of an infected mosquito transmits the sporozoite stage of the organism to humans. The parasite travels into the bloodstream and eventually makes its way to the liver, where it begins to multiply, producing merozoites. The merozoites leave the liver and enter red blood cells to reproduce. Soon, young parasites burst out in search of new red blood cells to infect.
Sometimes, the reproducing Plasmodia will create a form known as a gametocyte in the human bloodstream. If a mosquito takes a blood meal when gametocytes are present, the parasite begins to reproduce in the insect and create sporozoites that are infectious to people, completing the life cycle.
There are five species of Plasmodium that infect humans:
Clinicians who treat malaria in the United States are sometimes asked, "Is it contagious?" The answer is that malaria is not spread directly from person to person. A few cases have occurred in other countries through blood transfusion, intravenous drug abuse with shared needles, or organ transplantation. An infected mother can spread malaria through the placenta to her unborn child. Except for these rare situations, transmission occurs when a person is bitten by an infected mosquito and is not contagious to other individuals.
Medically Reviewed by a Doctor on 5/23/2014
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