What Is It?

Malaria is an infection caused by single-celled parasites that enter the blood through the bite of a female Anopheles mosquito. These parasites, called plasmodia, belong to four different species: Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale and Plasmodium malariae. All Plasmodium species spend one portion 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 red blood cells and/or liver cells. Infected blood cells eventually burst, sending waves of new Plasmodium parasites into the bloodstream and triggering malaria symptoms.

Most deaths from malaria are caused by P. falciparum, which causes severe disease because it is capable of infecting red blood cells of any age. The other Plasmodium species attack either immature or older cells. Young children and travelers, who lack natural immunity, and pregnant women are at highest risk of complications. Also, in patients with P. vivax or P. ovale infections, some Plasmodium parasites remain dormant inside the liver and can trigger malaria relapses months or years later. Because Plasmodium parasites are carried in the blood, malaria also can be spread through contaminated blood transfusions, transplanted 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 million to 2 million deaths every year. It is a tropical disease that is rare in the United States, where almost all cases are seen in people who have traveled from foreign countries where malaria is common. In the tropics, the particular species of Plasmodium varies from country to country and, 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:

  • High fever (up to 105 degrees Fahrenheit) with shaking chills
  • Profuse sweating when the fever suddenly drops
  • Fatigue
  • Headache
  • Muscle aches
  • A general feeling of sickness (malaise)
  • Abdominal discomfort
  • Nausea, vomiting
  • Feeling faint when you stand up or sit up quickly

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:

  • Brain involvement, which can produce extreme sleepiness, delirium, unconsciousness, convulsions and coma
  • Pulmonary edema, a dangerous accumulation of fluid inside the lungs that interferes with breathing (a common complication in pregnant women)
  • Kidney failure
  • Severe anemia, resulting from the destruction of infected red blood cells and decrease in the production of new red blood cells


Your doctor may suspect that you have malaria based on your symptoms and your history of foreign travel. Your doctor will examine you, but he or she may find only general signs, such as a fever and, in some cases, an enlarged spleen, that can occur in many diseases. 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 the presence of Plasmodium parasites. Other 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.

Expected Duration

With proper treatment, symptoms of malaria usually resolve 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, but full immunity to the disease does not occur.


There is no vaccine to protect against malaria. To prevent getting the disease, you can avoid mosquitoes and take preventive (prophylactic) medications. Travelers are especially vulnerable to developing severe disease because they lack the immunity that develops in people who live in a region that has malaria. Therefore, it is essential to take preventive, antimalarial medications when you travel to regions of the world that have malaria. Keep in mind, however, that these medications are not foolproof. 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:

  • Chloroquine (Aralen) — This is the most commonly prescribed antimalarial medication to prevent chloroquine-sensitive malaria. This medication is taken once a week, from one to two weeks prior to your departure until four weeks after you return. The two most commonly prescribed forms of this drug are chloroquine phosphate (Aralen Phosphate) and hydroxychloroquine sulfate (Plaquenil). This regimen is well tolerated by most people, with a few patients experiencing nausea, itching, dizziness, blurry vision and headache. You can minimize these symptoms by taking the drug after meals.

  • Mefloquine (Lariam) — This is the treatment of choice for travel to most regions of sub-Saharan Africa and other areas with high levels of chloroquine-resistant disease. Like chloroquine, the medication is taken once a week, from one to two weeks before departure until four weeks after your return. Common side effects include bad dreams, concentration difficulties, nausea and dizziness. Psychosis and seizures can occur, but they are rare and occur in only about one in every 10,000 users. However, you should not take this medication if you have conduction or rhythm disturbances in your heart, seizures or neuropsychiatric disease.

  • Doxycycline (Apo-Doxy, Doryx, Doxy-Caps, Monodox, Vibramycin) — This medication commonly is prescribed for travelers who are intolerant of chloroquine or mefloquine and is for people traveling to certain parts of Thailand, Cambodia and Myanmar. Doxycycline should be taken once per day, from two days before departure to four weeks after you return. It’s important to protect yourself diligently from sun exposure while you are taking doxycycline because it can cause you to be more sensitive to the sun, increasing your risk of sunburn. Pregnant women and young children should not take this drug.

  • Atovaquone and proguanil (Malarone) — This drug commonly is prescribed for the prevention of chloroquine-resistant malaria. You need to take one tablet at about the same time each day, starting one to two days before departure until seven days after your return. The most common side effects of Malarone include abdominal pain, nausea, vomiting and headache. You should not take this medication if you are pregnant or breastfeeding or you have severe kidney disease.

In addition to one of these medications, you also may need to take a medication called primaquine (sold as a generic) when you return from a long stay in an area of the world where P. vivax or P. ovale are common in case you have these organisms in your liver. Primaquine is taken daily for two weeks after you have left the area where malaria is common. People with a genetic disorder involving the red blood cells called G6PD deficiency cannot take primaquine, because they can develop severe anemia.

There are potential drug interactions between some of the medications used to treat HIV and those used to treat malaria. If you are HIV-positive, you should check with your doctor before taking malaria medications.

It is also essential that you decrease your risk of mosquito bites with the following strategies:

  • As much as possible, remain indoors in well-screened areas, especially at night when mosquitoes are most active.
  • Use mosquito nets and bed nets. It’s best to treat them with the insect repellant permethrin.
  • Wear clothing that covers most of your body.
  • Use an insect repellent, such as DEET, on uncovered skin. Ask your pediatrician which low-concentration DEET products are safe for children.
  • Apply permethrin to clothing.


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 most commonly used include chloroquine, quinidine (Cardioquin, Quinaglute Dura-tabs, Quinidex Extentabs, Quin-Release), atovaquone (Mepron), proguanil (sold as a generic), mefloquine, clindamycin (Cleocin) and doxycycline.

Patients with falciparum malaria tend to have the most severe symptoms. If they develop brain or kidney involvement, they probably will require treatment in the intensive care unit of a hospital.

For pregnant women, chloroquine is the preferred treatment for malaria. Quinine, sulfadoxine, pyrimethamine and clindamycin typically are used for pregnant patients with malaria that is resistant to chloroquine.

When To Call A Professional

Call your doctor before you travel to a tropical country where malaria is common, especially if you are pregnant or if your children will accompany you. After you return, call your doctor immediately if you develop symptoms of malaria, even if you think that it’s just a virus or only the flu, because falciparum malaria can cause death rapidly.


In the United States, most people with malaria have an excellent prognosis if they are treated properly with antimalarial drugs. However, people with falciparum malaria generally have the most serious illness, the greatest risk of complications, and the greatest danger of death. P. falciparum is most likely to cause severe disease among young children, pregnant women and travelers who are exposed to malaria for the first time. More than 30 percent of people with severe infection die, even with advanced medical treatment in an intensive care unit. Without treatment, the risk of death or complications is much higher, and untreated malaria that has affected the brain is nearly always fatal.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.