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Malaria (cont.)

Malaria Causes

Malaria is caused by protozoa of the genus Plasmodium and is transmitted 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 by 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:

  • P. vivax: This species is most commonly found in Asia, Latin America, and parts of Africa. Infections can sometimes lead to life-threatening rupture of the spleen. This type of malaria can hide in the liver (this is called the "hepatic phase" of the life cycle). It may then return later to cause a relapse years after the first infection. Special medications are used to eradicate P. vivax from the liver.
  • P. ovale: This species is rarely found outside Africa or the western Pacific islands. Symptoms are similar to those of P. vivax. Like P. vivax, P. ovale can hide in the liver for years before bursting out again and causing symptoms.
  • P. malariae: It is found worldwide but is less common than the other forms. This form of malaria is hard to diagnose because there are usually very few parasites in the blood. If untreated, the infection can last many years.
  • P. falciparum: This is the most life-threatening species of malaria. Although present throughout much of the tropical and subtropical world, it is particularly common in sub-Saharan Africa. P. falciparum is resistant to many of the older drugs used to treat or prevent malaria. Unlike P. vivax and P. ovale, this species does not hide in the liver.
  • P. knowlesi: Found predominantly in Malaysia, this species can also cause high levels of parasites in the blood, leading to organ failure or death.

Malaria Transmission

Is Malaria Contagious?

Fortunately, malaria is not contagious except in rare situations; it is not spread directly from person to person with the following exceptions. 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 only occurs when a person is bitten by an infected mosquito. The infected person is not contagious to other individuals, and there is no need to isolate or quarantine the person to protect others from direct transmission. However, depending on the local public-health situation, an infected traveler returning home may be asked to stay indoors until well. Some areas may have mosquitoes that are able to transmit malaria, and transmission of malaria from a returning traveler by local mosquitoes has been reported. Public-health authorities may increase mosquito-control measures in the area, as well, to reduce this risk.

Medically Reviewed by a Doctor on 5/1/2015

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Malaria »

Malaria, which predominantly occurs in tropical areas, is a potentially life-threatening disease caused by infection with Plasmodium protozoa transmitted by an infective female Anopheles mosquito vector.

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