Malaria is an infection caused by single-celled parasites that enter the blood through the bite of an Anopheles mosquito. These parasites, called plasmodia, belong to at least five species. Most human infections are caused by either Plasmodium falciparum or Plasmodium vivax. Plasmodium parasites spend several parts of their life cycle inside humans and another part inside mosquitoes. During the human part of their life cycle, Plasmodium parasites infect and multiply inside liver cells and red blood cells. Some infected blood cells burst because of the multiplying parasites inside. Many more infected red blood cells are broken down by your spleen or liver, which filter out and remove damaged or aging red blood cells from circulation. Both Plasmodium parasites in the bloodstream and irritants that are released from broken red blood cells cause malaria symptoms.
Most deaths from malaria are caused by P. falciparum, which causes severe disease. Before P. falciparum malaria causes a red blood cell to burst, it can make the surface of the cell stick to other cells like it. This causes the blood to clot within small blood vessels, which can severely damage organs.
People who have lived all their life in a country with a high rate of malaria have typically been exposed to malaria parasites many times. After the first exposure, your immune system begins to protect you, so re-infection may cause few or no symptoms. Your immune system does not remain active against malaria for more than a few years if you are not exposed again. This explains why people can live for years in the tropics without being bothered by malaria. However, people from the tropics who spend several years in another country may lose their immune protection. People who have never had a malaria infection (such as young children and travelers) and pregnant women are more likely to have severe symptoms from malaria.
Usually, symptoms appear within the first several weeks after the infected mosquito bites you. In people with P. vivax or P. ovale infections, it is possible for some Plasmodium parasites to remain inside the liver. If this happens, dormant parasite forms can become active and trigger malaria symptoms months or years after the first exposure.
In regions where there is a high rate of malaria infection, malaria can be spread in other ways than through a mosquito bite, such as through contaminated blood transfusions, transplantation of contaminated organs and shared drug needles. In pregnant women, malaria infection can pass through the bloodstream to the developing fetus, causing low birth weight or fetal death. This is most common with P. falciparum infection.
Malaria is one of the major causes of preventable death in the world today. It affects more than 500 million people worldwide and causes 1 to 2 million deaths every year. It is a tropical disease. Therefore, it is rare in the United States and European countries, where almost all cases are seen in people who have traveled from countries where malaria is common.
In the tropics, the particular species of Plasmodium varies from country to country. In some areas, new strains of malaria have emerged that are resistant to some antimalarial drugs. This emergence of drug-resistant strains has complicated the treatment and prevention of malaria in tropical countries and in travelers.
Symptoms of malaria can begin as early as six to eight days after a bite by an infected mosquito. They include:
If treatment is delayed, more severe complications of malaria can occur. Most people who develop these complications are infected with the P. falciparum species. They include:
Your doctor may suspect that you have malaria based on your symptoms and your history of foreign travel. When your doctor examines you, he or she may find an enlarged spleen because the spleen commonly swells during a malaria infection. To confirm the diagnosis of malaria, your doctor will take samples of blood to be smeared on glass slides. These blood smears will be stained with special chemicals in a laboratory and examined for Plasmodium parasites. Blood tests will be done to determine whether malaria has affected your levels of red blood cells and platelets, the ability of your blood to clot, your blood chemistry, and your liver and kidney function.
With proper treatment, symptoms of malaria usually go away quickly, with a cure within two weeks. Without proper treatment, malaria episodes (fever, chills, sweating) can return periodically over a period of years. After repeated exposure, patients will become partially immune and develop milder disease.
Researchers are working to create a vaccine against malaria. Vaccination is expected to become an important tool to prevent malaria in the future.
One way to prevent malaria is to avoid mosquito bites with the following strategies:
It is strongly recommended that you take preventive medication when you travel to a region of the world that has malaria. Keep in mind that these medications can prevent most malaria infections, but travelers occasionally get malaria even when they are taking one of these drugs. If you develop an illness with fever within a year of your return, seek immediate medical attention and tell a health care professional about your travel.
The four antimalarial medications most commonly prescribed in the United States for foreign travel include:
In addition to one of these medications, you also may need to take a medication called primaquine (sold as a generic) when you return home if you stayed for more than several months in an area of the world where you had heavy exposure to mosquitoes. This extra precaution eliminates dormant forms of malaria that may have entered your liver and survived even though you were taking preventive medication during your trip. Primaquine is taken daily for two weeks after you have left the area where malaria is common. People with a genetic shortage of a normal enzyme (G6PD deficiency) cannot take primaquine because they can develop severe anemia.
There are potential drug interactions between some of the medications used to treat human immunodeficiency virus (HIV) and those used to treat malaria. If you are HIV-positive, you should check with your doctor before taking malarial medications.
Malaria is treated with antimalarial drugs and measures to control symptoms, including medications to control fever, antiseizure medications when needed, fluids and electrolytes. The type of medications that are used to treat malaria depends on the severity of the disease and the likelihood of chloroquine resistance. The drugs available to treat malaria include:
People with falciparum malaria have the most severe symptoms. People with falciparum malaria may need to be monitored in the intensive care unit of a hospital during the first days of treatment because the disease can cause breathing failure, coma and kidney failure.
For pregnant women, chloroquine is the preferred treatment for malaria. Quinine, proguanil and clindamycin typically are used for pregnant people with malaria that is resistant to chloroquine.
See your doctor before you travel to a tropical country where malaria is common, so that you can take medications to prevent malaria. After you return, call your doctor if you develop a high fever within the first several months.
In the United States, most people with malaria have an excellent prognosis if they are treated properly with antimalarial drugs. Without treatment, malaria can be fatal, particularly P. falciparum. People with severe malaria have the greatest danger of death. From 10% to 40% of people with severe malaria die even with advanced medical treatment. P. falciparum is more likely to cause severe disease among young children, pregnant women and travelers who are exposed to malaria for the first time.
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