MalariaViruses

Malaria is a parasitic infection spread by Anopheles mosquitoes. The Plasmodium parasite that causes malaria is neither a virus nor a bacterium – it is a single-celled parasite that multiplies in red blood cells of humans as well as in the mosquito intestine.

When the female mosquito feeds on an infected person, male and female forms of the parasite are ingested from human blood. Subsequently, the male and female forms of the parasite meet and mate in the mosquito gut, and the infective forms are passed onto another human when the mosquito feeds again.

Malaria is a significant global problem. There are approximately 216 million cases of the disease worldwide, killing about 655,000 people every year. Malaria is prevalent in Africa, Asia, the Middle East, Central South America, Hispaniola (Haiti and the Dominican Republic), and Oceania (Papua New Guinea, Irian Jaya, and the Solomon Islands). However, malaria is most prevalent in Africa where 60% of all cases are reported. In Canada, malaria is most often caused by travel to and from endemic areas.

Each year, up to 1 million Canadians travel to malaria-endemic areas. This results in 350 to 1,000 annual cases of malaria in Canada and 1 to 2 deaths per year.

Although the parasite has progressively developed resistance to several older anti-malarial medications, there are still many safe and effective medications both for treatment and prevention.

There are four species of the Plasmodium parasite that can cause malaria in humans: P. falciparum, P. vivax, P. ovale, and P. malariae.The first two types are the most common. Plasmodium falciparum is the most dangerous of these parasites because the infection can kill rapidly (within several days), whereas the other species cause illness but not death. Falciparum malaria is particularly frequent in sub-Saharan Africa and Oceania.

Causes of Malaria

You can only get malaria if you're bitten by an infected mosquito, or if you receive infected blood from someone during a blood transfusion. Malaria can also be transmitted from mother to child during pregnancy.

The mosquitoes that carry Plasmodium parasite get it from biting a person or animal that's already been infected. The parasite then goes through various changes that enable it to infect the next creature the mosquito bites. Once it's in you, it multiplies in the liver and changes again, getting ready to infect the next mosquito that bites you. It then enters the bloodstream and invades red blood cells. Eventually, the infected red blood cells burst. This sends the parasites throughout the body and causes symptoms of malaria.

Malaria has been with us long enough to have changed our genes. The reason why many people of African descent suffer from the blood disease sickle cell anemia is because the gene that causes it also confers some immunity to malaria. In Africa, people with a sickle cell gene are more likely to survive and have children. The same is true of thalassemia, a hereditary disease found in people of Mediterranean, Asian, or African American descent. (See the article on "Anemia" for more information.)

Symptoms and Complications of Malaria

Symptoms usually appear about 12 to 14 days after infection. People with malaria have the following symptoms:

• abdominal pain
• chills and sweats
• diarrhea, nausea, and vomiting (these symptoms only appear sometimes)
• headache
• high fevers
• low blood pressure causing dizziness if moving from a lying or sitting position to a standing position (also called orthostatic hypotension)
• muscle aches
• poor appetite

In people infected with P. falciparum, the following symptoms may also occur:

• anemia caused by the destruction of infected red blood cells
• extreme tiredness, delirium, unconsciousness, convulsions, and coma
• kidney failure
• pulmonary edema (a serious condition where fluid builds up in the lungs, which can lead to severe breathing problems)

P. vivax and P. ovale can lie inactive in the liver for up to a year before causing symptoms. They can then remain dormant in the liver again and cause later relapses.P. vivax is the most common type in North America.