What Is Malaria?

Malaria is a disease that is caused by a parasite, a living thing that lives and feeds on another living thing without helping its host in any way. The parasites that cause malaria are tiny, single-celled creatures known as protozoa. The four types of protozoa that cause malaria all belong to a category known as Plasmodium. Of these, Plasmodium falciparum is the most common and the deadliest.

Malaria parasites are spread to humans by the bite of an infected Anopheles mosquito. Such mosquitoes are found in almost all countries in the tropics (region around the equator) and subtropics (region just beyond the tropics).

In fact, malaria is a public health problem in more than 90 countries, where two out of every five people in the world live. There are 300 to 500 million cases of malaria each year, and more than 1 million of these cases lead to death. Although malaria is found around the world, more than 9 out of 10 cases occur in Africa south of the Sahara Desert. Most of the deaths there occur among young children, especially in rural areas where the people cannot reach good medical care. This is especially unfortunate because malaria can be cured if it is diagnosed early and treated promptly.

There are about 2,700 species of mosquitoes, including more than 90 species of Anopheles mosquitoes, many of which carry malaria. Anopheles mosquitoes typically bite between dusk and dawn. Only female mosquitoes suck blood and, thus, spread malaria. This is the female Anopheles gambiae mosquito seen up close and personal under an electron micro-scope.

How Does the Malaria Parasite Cause Disease?
The Plasmodium parasite that causes malaria is carried by the Anopheles mosquito. When an infected mosquito bites a person, it can pass tiny, immature forms of the parasite into the person's body. The immature parasites travel through the person's blood-stream to the liver, where they develop and multiply.

The parasites then reenter the bloodstream and invade the red blood cells, which carry oxygen from the lungs throughout the body. Some of the parasites reach a sexual stage. If these are sucked up by another mosquito drinking its next blood meal, they can meet in the mosquito's gut. There, they can start a whole new generation of malaria parasites.

While in the red blood cells, the parasites continue to multiply. After 48 to 72 hours, the red blood cells break open and release more parasites into the bloodstream. The person then has symptoms such as chills, fever, and headache. The fever lasts for several hours. Then the person starts sweating and his body temperature falls. This cycle of symptoms comes and goes every 48 to 72 hours, following the life cycle of the parasites. Each cycle worsens the person's anemia, or lack of red blood cells. As a result, less and less oxygen reaches the brain and other organs.

Who Is at Risk?
Malaria is mainly a problem in poor countries. Rural areas in such countries are hit particularly hard. Mosquitoes are most likely to spread malaria during the rainy season, when families in these areas are busy farming. Illness then makes it tougher for them to survive. There are about 1,000 cases of malaria a year in the United States, mostly among travelers returning from such areas.

Malaria is a special threat to young children in places where it is common. Worldwide, about 3,000 children under age five die of the disease each day. Malaria is also particularly dangerous for women who are pregnant. It may increase the risk of the baby being born early or dying before or at birth.

What Are the Symptoms?
The symptoms of malaria include chills, fever, sweating, headache, muscle aches, and tiredness. Other possible symptoms include vomiting, diarrhea, and coughing. In its early stage, the disease may be mild, resembling the flu. If it is not treated, however, malaria caused by the Plasmodium falci-parum parasite may get much worse, leading to liver and kidney failure, seizures, coma, and sometimes death.

Although the symptoms caused by other Plasmodium parasites are less severe, the parasites can remain in an inactive state in the liver for long periods. Later, the parasites can become active again, and the symptoms can reappear after months or even years.

The first symptoms of malaria usually start within one to three weeks after a person is bitten by an infected mosquito. However, the time can stretch to several months in some cases. Travelers who come down with a fever or flu-like illness during or after a trip to an area where malaria is a problem should see a doctor right away.

How Is Malaria Treated and Prevented?
To test for malaria, a doctor checks a blood sample for malaria parasites. If they are found, prompt treatment is critical. There are several drugs that can treat malaria effectively in its early stage. Even better, travelers can take these drugs before visiting risky areas to help prevent the disease.

Chloroquine is still used in parts of the world where the parasites have not yet developed resistance to this drug. In other parts of the world, the U.S. Centers for Disease Control and Prevention (CDC) now recommends that travelers take a drug called mefloquine.