When you're bitten by a malaria-infected mosquito, the parasites that cause malaria are injected into your blood and invade your liver cells. The parasite reproduces in the liver cells, which then burst open, allowing thousands of new parasites to enter the bloodstream and infect red blood cells. The parasites reproduce again in the blood cells, kill the blood cells, and then move to other uninfected blood cells.

The time from the initial malaria infection until symptoms appear (incubation period) generally ranges from:¹

• 9 to 14 days for Plasmodium (P.) falciparum.
• 12 to 18 days for P. vivax and P. ovale.
• 18 to 40 days for P. malariae.

Symptoms can appear in 7 days. Occasionally, the time between exposure and signs of illness may be as long as 8 to 10 months with P. vivax and P. ovale, because these parasites can survive in the human liver for a long time.

The incubation period may be longer if you are taking medicine to prevent infection (chemoprophylaxis) or have developed partial immunity due to previous infections.

Malaria can begin with flu-like symptoms. In the early stages, infection from P. falciparum is similar to infection from P. vivax, P. malariae, and P. ovale. You may have no symptoms or symptoms that are less severe if you are immune or partially immune to malaria.

Common malaria symptoms include:

• Fever.
• Chills and a rapidly rising temperature.
• Headaches, nausea, and extreme sweating.

Symptoms may appear in cycles. The time between episodes of fever and other symptoms varies with the specific parasite you are infected with. Episodes of symptoms may occur:

• Every 48 hours if you are infected with P. vivax or P. ovale.
• Every 72 hours if you are infected with P. malariae.
• P. falciparum does not usually have a regular, cyclic fever.

After the early stages, life-threatening complications develop rapidly with P. falciparum and, if untreated, may result in irreversible complications or death.²

If untreated, you may recover in a week to a month (or longer) after being infected with P. vivax, P. malariae, or P. ovale.

Malaria can be a very serious disease for a pregnant woman and her unborn baby (fetus), and for young children. Medication choices are limited for a pregnant woman or a child. Infection with P. falciparum can lead to death for a pregnant woman and her fetus. For these reasons, a pregnant woman should not travel to an area where she could get P. falciparum malaria. Visit the CDC Web site (www.cdc.gov/malaria/travel/index.htm) to find out whether malaria is a problem in the country where you will be traveling.

Malaria recurrences

Malaria caused by P. falciparum may come back (recur) at irregular intervals for up to 2 years if treatment is not complete.

Malaria caused by P. vivax and P. ovale may recur at irregular intervals for up to 3 to 4 years, but medication treatment can prevent relapses.

P. malariae can remain in the blood of an infected person for more than 30 years, usually without causing any symptoms.