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Malaria occurs in over 100 countries and territories. More than 40% of the people in the world are at risk of getting malaria. Large areas of Central and South America, Haiti, the Dominican Republic, Africa, the Indian subcontinent, Southeast Asia, the Middle East, and Oceania are considered malaria-risk areas.

Malaria is caused by a parasite that is transmitted from person to person by the bite of an infected mosquito. When a mosquito bites an infected person, it ingests microscopic malaria parasites found in the person’s blood. The malaria parasite must grow in the mosquito for a week or more before infection can be passed to another person. If, after a week, the mosquito then bites another person, the parasites go from the mosquito’s mouth into the person’s blood.

The parasites then travel to the person’s liver, enter the liver’s cells, grow, and multiply. During this time when the parasites are in the liver, the person has not yet felt sick. The parasites leave the liver and enter red blood cells; this may take as little as 8 days or as many as several months. Once inside the red blood cells, the parasites grow and multiply. The red blood cells burst, freeing the parasites to attack other red blood cells. Toxins from the parasite are also released into the blood, making the person feel sick. If a mosquito bites this person while the parasites are in his or her blood, it will ingest the tiny parasites. After a week or more, the mosquito can infect another person.

Each year in the United States, a few cases of malaria result from blood transfusions, are passed from mother to fetus during pregnancy, or are transmitted by locally infected mosquitoes.

Only certain mosquitoes can transmit malaria. These mosquitoes are present in almost all countries in the tropics and subtropics. They are active only during the evening and night, from dusk to dawn. Therefore, it is very unlikely that you will be infected with malaria during daylight hours. The symptoms of malaria include fever, chills, headache, muscle ache, and malaise. Early stages of malaria may resemble flu.

Malaria can often be prevented by the use of drugs, and by using individual protection measures against mosquitoes. The need for malaria prevention and the kind of measures depend on the itinerary of the traveler, the duration of travel, and the place where the traveler will spend the evenings and nights.

Travelers to malarious areas should use drugs to prevent malaria and take measures to avoid being bitten by mosquitoes. However, they can still get malaria, despite use of prevention measures. Malaria symptoms can develop as early as six days after the first exposure to infected mosquitoes in a malaria endemic area, or as late as several months after departure from a malarious area, even after preventative drugs are discontinued. Malaria can be treated effectively in its early stages, but delaying treatment can have serious consequences.

Persons who become ill with a fever during or after travel in a malarious area should seek prompt medical attention and should inform their physician of their recent travel. Neither the traveler nor the physician should assume that the traveler has the flu or some other disease without doing a laboratory test to determine if the symptoms are caused by malaria.

Malaria is diagnosed by looking for the parasites in a drop of blood. Blood is put onto a microscope slide and stained so that the parasites are visible under a microscope.

Any traveler who becomes ill with a fever or flu-like illness while traveling and up to 1 year after returning home should immediately seek professional medical care. You should tell your health care provider that you have been traveling in a malaria-risk area.

Malaria can be cured with prescription drugs. The type of drugs and length of treatment depend on which kind of malaria is diagnosed, where the patient was infected, the age of the patient, and how ill the patient was at start of treatment.

All travelers to areas of the world where malaria is present are advised to use the appropriate drug regimen and personal protection measures to prevent malaria. The regional information provided by different travel services may specify both the appropriate drug regimen and personal protection measures for the area to which you are traveling, so be sure to check with your travel agency.

In addition to using drugs to prevent malaria, travelers should use measures to reduce exposure to malara-carrying mosquitoes, which bite during the evening and night. To reduce mosquito bites, travelers should remain in a well-screened area, use mosquito nets, and wear clothes that cover most of the body.