What is Malaria?
Malaria is a mosquito-borne disease that causes over 2.7 million deaths per year according to estimates by the World Health Organization. "Malaria is a serious and sometimes fatal disease caused by a parasite that commonly infects a certain type of mosquito which feeds on humans. People who get malaria are typically very sick with high fevers, shaking chills and flu-like illness. Four kinds of malaria parasites can infect humans: Plasmodium falciparum, P. vivax, P. ovale, and P. malariae. Infection with P. falciparum, if not promptly treated, may lead to death. Although malaria can be a deadly disease, illness and death from malaria can usually be prevented." (Source: www.cdc.gov/malaria, December 2007).
Mosquito-Borne DiseasesMalaria is a disease of the blood that is transmitted to people by infected mosquitoes; a potentially fatal blood disease caused by a parasite that is transmitted to human and animal hosts by the Anopheles mosquito. Malaria is caused by any one of four species of one-celled parasites, called Plasmodium. The parasite is spread to people by the female Anopheles mosquito, which feeds on human blood.
Although four species of malaria parasites can infect humans and cause illness, only malaria caused by Plasmodium falciparum is potentially life-threatening.
The human parasite, Plasmodium falciparum is dangerous not only because it digests the red blood cell's hemoglobin, but also because it changes the adhesive properties of the cell it inhabits. This change in turn causes the cell to stick to the walls of blood vessels. It becomes especially dangerous when the infected blood cells stick to the capillaries in the brain, obstructing blood flow, a condition called cerebral malaria.
How is malaria spread?A person gets malaria from the bite of an infected female mosquito. The mosquito bite injects young forms of the malaria parasite into the person's blood. The parasites travel through the person's bloodstream to the liver, where they grow to their next stage of development. In 6 to 9 days, the parasites leave the liver and enter the bloodstream again. They invade the red blood cells, finish growing, and begin to multiply quickly. The number of parasites increases until the red blood cells burst, releasing thousands of parasites into the person's bloodstream. The parasites attack other red blood cells, and the cycle of infection continues, causing the common signs and symptoms of malaria.
When a non-infected mosquito bites an infected person, the mosquito sucks up parasites from the person's blood. The mosquito is then infected with the malaria parasites. The parasites go through several stages of growth in the mosquito. When the mosquito bites someone else, that person will become infected with malaria parasites, and the cycle will begin again.
Malaria parasites can also be transmitted by transfusion of blood from an infected person or by the use of needles or syringes contaminated with the blood of an infected person. A mother also can transmit malaria to her infant before or during delivery.
What are the signs and symptoms of malaria?People with malaria typically have cycles of chills, fever, and sweating that recur every 1, 2, or 3 days. The attack of the malaria parasites on the person's red blood cells makes the person's temperature rise and the person feels hot. The subsequent bursting of red blood cells makes the person feel cold and have hard, shaking chills. Nausea, vomiting, and diarrhea often go along with the fever. The destruction of red blood cells can also cause jaundice (yellowing of the skin or whites of the eyes) and anemia.
How soon after exposure do symptoms appear?The time between a mosquito bite and the start of illness is usually 7 to 21 days, but some types of malaria parasites take much longer to cause symptoms. When infection occurs by blood transfusion, the time to the start of symptoms depends on the number of parasites in the transfusion.
Is malaria an emerging infectious disease?Yes. Many countries have been experiencing a resurgence in cases caused by Plasmodium falciparum, the most deadly of the four human malaria parasites. Urban migration, poverty, and poor sanitation have returned malaria to cities where it once was eliminated. New roads, lodging, and irrigation have drawn people into once-isolated areas where mosquitoes thrive. Refugees, migrants, and tourists have spread the disease across borders.
The seriousness of the worldwide re-emergence of malaria is made worse by the spread of parasites that are resistant to anti-malaria drugs. Parasites, like bacteria and viruses, can develop resistance to the drugs used to prevent or treat infection. Malaria parasites are increasingly resistant to chloroquine, the drug most widely used for prevention and treatment. Chloroquine-resistant strains have been reported from areas in Africa, Asia, and the Americas.
The potential also exists for malaria to become re-established in the United States. Currently, about 1,200 malaria cases are reported each year in the United States. Almost all occur in persons who were infected in other parts of the world (imported malaria). Small outbreaks of non-imported malaria, the result of transmission from imported cases, have also been reported. So far, the outbreaks have been quickly and easily contained. A continued increase in drug-resistant malaria throughout the world, however could increase the number of cases of imported malaria and improve the chances for malaria to re-emerge in the United States.
How is malaria diagnosed?Malaria is diagnosed by a blood test to check for parasites.
Who is at risk for malaria?Anyone who lives in or travels to a country where there are malaria-infected people and mosquitoes is at risk.
What complications can result from malaria?Malaria caused by Plasmodium falciparum can cause kidney or liver failure, coma, and death. Although infections with other malaria parasites cause less serious illness, parasites can remain inactive in the liver and cause a reappearance of symptoms months or even years later.
What is the treatment for malaria?The treatment for malaria depends on where a person is infected with the disease. Different areas of the world have malaria types that are resistant to certain medicines. The correct drugs for each type of malaria must be prescribed by a doctor. Infection with Plasmodium falciparum is a medical emergency. About 2% of persons infected with falciparum malaria die, usually because of delayed treatment.
How common is malaria?Worldwide, an estimated 350-500 million malaria infections occur each year, with 2 million to 3 million deaths. Most deaths are from infection with Plasmodium falciparum.
About 1,200 cases of malaria are diagnosed in the United States each year. Most are in persons entering the country for the first time or returning from foreign travel. A very small number of cases are the result of direct transmission involving mosquitoes that live in the United States. Most of these have occurred in Mexican farm workers living in California in poor conditions.