Malaria

What is malaria?

Malaria is a serious disease that causes a high fever and chills. You can get it from a bite by an infected mosquito. Malaria is rare in the United States. It is most often found in Africa, Southern Asia, Central America, and South America.

What causes malaria?

Malaria is caused by a bite from a mosquito infected with certain germs called parasites. In very rare cases, people can get malaria if they come into contact with infected blood. An unborn baby (fetus) may get the disease from its mother. You cannot get malaria just by being near a person who has the disease.

What are the symptoms?

Most malaria infections cause symptoms like the flu, such as a high fever, chills, and muscle pain. Symptoms tend to come and go in cycles. One type of malaria may cause more serious problems, such as damage to the heart, lungs, kidneys, or brain. It can even be deadly.

How is malaria diagnosed?

Your doctor will order a blood test to check for the malaria parasite in your blood.

How is it treated?

Medicines usually can treat the illness. But some malaria parasites may survive because they are in your liver or they are resistant to the medicine.

Call a doctor right away if you have been in an area where malaria is present, were exposed to mosquitoes, and get symptoms that are like the flu. These include a high fever, chills, and muscle pain.

How is malaria prevented?

You may be able to prevent malaria by taking medicine before, during, and after travel to an area where malaria is present. But using medicine to prevent malaria doesn't always work. This is partly due to the parasites being resistant to some medicines in some parts of the world.

Frequently Asked Questions

A bite from a parasite-infected mosquito causes malaria. There are four species of Plasmodium(P.) parasites that infect mosquitoes.

Infection with P. falciparum

• P. falciparum is found mostly in the tropics and subtropics (near the equator).
• Infection with P. falciparum can lead to life-threatening complications after the first few days.
• P. falciparum is often resistant to a popular antimalarial medication (chloroquine) and needs treatment with other medications.

Infection with P. vivax, P. malariae, or P. ovale

• P. vivax and P. malariae occur all over the tropical regions of the world. P. ovale is found in western Africa.
• Infection with any of these three types of malaria usually is not life-threatening, and a person may recover in a month without treatment.
• P. vivax, P. malariae, and P. ovale generally are not as drug-resistant as P. falciparum.
• P. vivax and P. ovale may stay in the liver, requiring further treatment with medicine to prevent relapses.

How the disease spreads

Malaria is spread when an infected Anopheles mosquito bites a person. Only this type of mosquito can spread malaria. The mosquito becomes infected by biting an infected person and drawing blood that contains the parasite. When that mosquito bites another person, that person becomes infected.

In the United States, people who develop malaria are nearly always found to have contracted it while traveling in parts of the world where malaria is common. For more information, see the topic Travel Health.

When symptoms appear

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.

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

Variation in symptoms

In regions where malaria is present, people may have the disease but—due to immunity or semi-immunity—they have few or no symptoms.² The severity of malaria symptoms can also vary depending on your immunity, your general health, and whether you still have your spleen.

Common symptoms of malaria

In the early stages, malaria symptoms are sometimes similar to those of many other infections caused by bacteria, viruses, or parasites. Symptoms may include:

• Fever.
• Chills.
• Headache.
• Sweats.
• Fatigue.
• Nausea and vomiting.

Symptoms may appear in cycles and may come and go at different intensities and for different lengths of time. However, especially at the beginning of the illness, the symptoms may not follow this typical pattern.

The cyclic pattern of malaria symptoms is due to the life cycle of malaria parasites as they develop, reproduce, and are released from the red blood cells and liver cells in the human body. This cycle of symptoms is also one of the major indicators that you are infected with malaria.

Other common symptoms of malaria

Other common symptoms of malaria include:

• Dry (nonproductive) cough.
• Muscle and/or back pain.
• Enlarged spleen.

Rarely, malaria can lead to impaired function of the brain or spinal cord, seizures, or loss of consciousness.

Infection with the P. falciparum parasite is usually more serious and may become life-threatening.

There are other conditions with symptoms similar to a malarial infection. It is important that you see your doctor to discover the cause of your symptoms.

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.

Factors that increase your risk of getting malaria include:

• Living or traveling in a country or region where malaria is present.
• Traveling in an area where malaria is common and:
  • Not using preventive medication therapy before, during, and after travel, or failing to take the medicine correctly.
  • Being outdoors, especially in rural areas, between dusk and dawn (nighttime), when the mosquitoes that transmit malaria are most active.
  • Not taking steps to protect yourself from mosquito bites.

Your risk of getting malaria depends on your age, history of exposure to malaria, and whether you are pregnant.³ Most adults who have lived in areas where malaria is present have developed partial immunity to malaria because of previous infections and therefore almost never develop severe disease. However, young children who live in these areas and travelers to these areas are especially at risk for malaria because they have not developed this immunity.

Pregnant women are more likely than nonpregnant women to get severe malaria, because the immune system is suppressed during pregnancy.³

In addition, pregnant women, young children, older adults, and people with other health problems are more likely to have serious complications if they get malaria.

You can take measures to reduce the risk of malaria if you live in areas where the disease is present, or if you are traveling in these areas.

Malaria is more severe in people who have had their spleen removed (splenectomy).

Call a doctor immediately if you have been in an area where malaria is present, were exposed to mosquitoes, and develop flu-like symptoms (such as fever, chills, headache, and nausea).

Watchful Waiting

Watchful waiting is a wait-and-see approach. If you get better on your own, you won't need treatment. If you get worse, you and your doctor will decide what to do next.

Do not wait to call a doctor if you think you have malaria. Call a doctor immediately.

For people who live for many years in countries where malaria is common and have some immunity to malaria, watchful waiting is okay for mild malaria symptoms. Flu-like symptoms may also be caused by many other diseases or health conditions. Watchful waiting is not appropriate for most travelers. If you have a question about your symptoms, call your doctor.

Who To See

Health professionals who can check out symptoms that may be caused by malaria include:

• Physician assistants or nurse practitioners.
• Family medicine physicians.
• Pediatricians.
• Internists.
• Infectious disease specialists.

In the United States, call the Centers for Disease Control and Prevention (CDC) toll-free at 1-877-394-8747 (1-877-FYI-TRIP) or visit the CDC's malaria Web site (www.cdc.gov/travel/regionalmalaria/index.htm) to receive the most current information about malaria and appropriate travel precautions. Your doctor or local health department may also have this information.

To prepare for your appointment, see the topic Making the Most of Your Appointment

Doctors use thick and thin blood smears to determine whether malaria-causing parasites are present in your blood. This test should be done if you have been in a region where malaria is present, were exposed to mosquitoes, and have developed flu-like symptoms.

• A blood smear is prepared from a blood sample.
• If the first blood smear does not show the presence of malaria parasites but your doctor suspects malaria, you should have a repeat test every 8 to 12 hours for 36 hours.
• During treatment, doctors use blood smears to see whether the number of malaria parasites in the blood is decreasing.

Other tests

Other useful tests that may be done include:

• Liver function tests, to check for liver damage.
• Complete blood count (CBC), to check for anemia or evidence of other possible infections. Anemia sometimes develops in people with malaria because the parasites damage red blood cells.
• A blood glucose test to measure the amount of a type of sugar, called glucose, in your blood.

New tests that quickly diagnose malaria are available in some parts of the world (not the United States). Testing has shown that they are reliable and easy to use.

Other tests under development to diagnose malaria include genetic tests or other blood tests that highlight parasites by using special stains. These experimental tests are not as easy to do and are not as frequently used as blood smears.

In the United States, malaria is an infectious disease that must be reported to the local or state health department.

Medication can prevent malaria and is necessary to treat the disease. Several factors influence the choice of medication, including:

• Whether the medicine is being used to prevent or to treat malaria.
• Your condition (such as your age or whether you are pregnant).
• How sick you are from malaria.
• Geographic location where you were exposed to malaria.
• Whether the malaria parasite may be resistant to certain medications.
• Your ability to take the preferred medicine without side effects or complications.
• Whether you are able to take the medication as a pill.

Malaria is rare in the United States, but it is widespread in other parts of the world. Find out about the risk for malaria before you travel internationally. The most accurate information about malaria risk and medication resistance in specific countries is from the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO).

If you have malaria, medication choice is based on:

• The specific parasite causing the infection.
• The severity of the infection.
• Your condition (such as age, pregnancy, allergies, or health problems).
• Medication resistance of the parasite found in the geographic area where you were infected.

If you have been in an area where malaria occurs, were exposed to mosquitoes, and develop flu-like symptoms, but tests do not show the malaria parasite in your blood, the tests should be repeated 3 or 4 times to confirm that you do not have a malaria infection. During medication treatment, tests are repeated to follow the course of the infection and to check whether the number of parasites is decreasing.

Your age and health condition are important factors in selecting a medication to prevent or treat malaria. Pregnant women, children, people who are very old, people who have other health problems, and those who did not use medication therapy to prevent malaria infection require special consideration.

Prevention of malaria involves protecting yourself against mosquito bites and taking antimalarial medications. However, public health officials strongly recommend that young children and pregnant women avoid traveling to areas where malaria is common.

The most current information about malaria is available from the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO). If you are planning international travel, you can learn about the risk of malaria in that geographic area and the medications recommended to prevent infection by contacting:

• The CDC at its toll-free phone number (1-877-394-8747) or Web site (www.cdc.gov/malaria/travel/index.htm).
• Your doctor or local health department.

Prevent mosquito bites

To prevent mosquito bites, follow these guidelines:

• Limit your outdoor activity between dusk and dawn. Stay in screened or air-conditioned rooms.
• Wear protective clothing (long pants and long-sleeved shirts).
• Use insect repellent with DEET (N,N diethylmetatoluamide). The repellent is available in varying strengths up to 100%. In young children, use a preparation containing less than 24% strength, because too much of the chemical can be absorbed through the skin.
• Use bed nets (mosquito netting) sprayed with or soaked in an insecticide such as permethrin or deltamethrin.
• Use flying-insect spray indoors around sleeping areas.
• Avoid areas where malaria and mosquitos are present if you are at higher risk (for example, if you are pregnant, very young, or very old).

If you use a bed net treated with insecticide and use insect repellents on your clothes, you will reduce your risk of becoming infected with malaria. Other steps that may be helpful in reducing the risk of malaria include using air conditioning and electric fans, wearing protective clothing, using aerosol insecticides in your house, and taking certain antimalarial medications.⁴

Drugs to prevent malaria

The selection of medications to prevent malaria depends on the geographic region where you may be exposed to malaria and your health condition (such as being pregnant, being elderly or young, being sick, or having immunity or resistance to malaria, or having allergies or sensitivity to the medication).

If you are going to a location where malaria is present, it is very important to take preventive medicines and to follow the correct schedule for taking them. The majority of people who become infected with malaria do not take preventive malaria medicines or do not follow the correct dosing schedule.

• Medicine to prevent malaria is most effective if you take the recommended dosage exactly as prescribed and for the length of time required.
• If you are to take the medicine once a week, take it on the same day of the week each week.
• Upon returning from an area where malaria is present, continue the medicine for the recommended length of time to ensure that all parasites have been eliminated from your body. You will need to take the medicine for 1 to 4 weeks after returning.

Malaria vaccines

Scientists are studying malaria vaccines to see whether the vaccines are effectively preventing malaria infection. To date, there is no strong evidence that these vaccines are effective.^{5, 4} Work continues on improving vaccines for preventing malaria.

If you plan to travel in remote areas where malaria is present, it is very important to take preventive medicines and to follow the correct schedule for taking them. The majority of people who become infected with malaria did not take preventive malaria medicines or did not follow the correct dosing schedule.

If you are going to areas where there is no medical care available, you can get medicine before you leave and carry it with you while you travel. Your doctor will give you instructions on how to use the medicine if you should develop malaria symptoms. This is a temporary measure until you can get medical care. Seek medical care as soon as possible (ideally within 24 hours).

The most current information about the prevention and treatment of malaria is from the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO). Contact the CDC at its toll-free phone number (1-877-394-8747) or Web site (www.cdc.gov/malaria). The WHO Web site is available at www.who.int/malaria.

You can take medicines called antimalarials to prevent and treat malaria. Malaria is a very serious disease, and its presence in many regions of the world is well known. Therefore, if you are traveling to an area where malaria is present, it is important to consider taking medicine before you travel, while you are in the area, and after you return home to reduce the risk of infection. Which medicine you take is based on:

• The country or areas in which you will be traveling.
• The resistance of malaria parasites to certain medicines in the area where you will be traveling.
• Your health condition (such as being pregnant, being elderly or young, being sick, or having immunity or resistance to malaria).
• Your ability to swallow medicine.

It is important to know which species of parasite is present because serious complications may develop in a person who is infected with Plasmodium (P.) falciparum. Drug treatment is based on:

• The species of parasite. If you are infected with P. falciparum, life-threatening complications can develop rapidly. Infection caused by one of the other three species of malaria is rarely life-threatening.
• The density of parasites. If the percentage of red blood cells infected (parasite density) is over 5%, treatment may include medications given directly into a vein (intravenously, or IV) rather than medicine taken by mouth.
• Your health condition. You are at increased risk for developing complications if you are pregnant, elderly, very young, or have a weak immune system. Different medicines may be prescribed for people in these groups.
• Drug resistance in the geographic area where the infection occurred. For instance, in many areas P. falciparum is resistant to the drug chloroquine.

During medication treatment of malaria, your doctor may sometimes do daily blood smears to follow the course of the infection. Most medicines for malaria are ones you take by mouth, but you might get intravenous (IV) medications if there are complications or your condition worsens. If there are no complications, your fever will clear in 36 to 48 hours, and most parasites will disappear from your blood within 2 or 3 days.

Drug therapy and treatment continue to change as medication resistance increases and new medicines are developed.

Medication Choices

There are several medications for preventing and treating malaria.

Medications to prevent malaria

A doctor or local health department can consult the CDC for specific treatment guidelines for your travel destination. Standard medicines for preventing malaria include:

• Chloroquine. Start treatment 1 to 2 weeks before you travel to areas where malaria is present. Continue to take it weekly during travel in areas where malaria is present and for 4 weeks after you leave these areas. You can take chloroquine to prevent P. falciparum and P. vivax infections in areas where medication resistance to chloroquine has not been confirmed.
• Mefloquine. Start treatment 1 to 2 weeks before you travel to areas where malaria is present. Continue to take it weekly during travel in areas where malaria is present and for 4 weeks after you leave these areas. Do not take mefloquine if you have a history of active or recent depression or other psychological conditions.
• Doxycycline. You can take doxycycline if you cannot take mefloquine. Start treatment 1 to 2 days before you travel to areas where malaria is present. Take it daily during travel in areas where malaria is present and for 4 weeks after you leave these areas. Women who are pregnant and children younger than age 8 should not take this medication.
• Primaquine. You take primaquine to prevent relapses of P. vivax and P. ovale. Take primaquine for 2 weeks after you leave the area where these parasites are present. (You should be tested for glucose-6-phosphate dehydrogenase deficiency before taking primaquine phosphate.)
• Malarone. Malarone is a combination of two antimalarial medications (atovaquone and proguanil HCL). Malarone is taken to prevent malaria caused by P. falciparum.⁶ Adults need to take one tablet daily 1 or 2 days before they enter an area where malaria is present and continue taking it daily throughout their stay. Then, you take it for 7 days after returning home.

Medications to treat infections

Chloroquine is the most effective medication for treating a malaria infection caused by P. ovale or P. malariae parasites. To prevent relapses of infections caused by these two parasites, continue taking chloroquine after you leave the area where these parasites are present.

Chloroquine is also used to treat P. falciparum and P. vivax infections in areas where medication resistance to chloroquine has not been confirmed.

Medications to treat chloroquine-resistant infections

When a malaria infection is caused by resistant strains of P. falciparum or P. vivax, treatment may be more difficult. When treatment with chloroquine does not work, you must take other medicines. These medicines may include:

• Mefloquine, for chloroquine-resistant P. falciparum infections outside of Thailand, Myanmar, and western Cambodia.
• Doxycycline, for infections caused by P. falciparum and P. vivax in Thailand and Kenya.
• Quinine sulfate plus an antibiotic such as doxycycline, tetracycline, or clindamycin for most P. falciparum infections. It should not be used in Southeast Asia, where quinine effectiveness is declining. It is only somewhat effective in Thailand.
• Quinine sulfate plus pyrimethamine-sulfadoxine, for chloroquine-resistant P. falciparum infections.
• Quinine sulfate plus clindamycin, given to children younger than age 8 and women who are pregnant.

You can get antimalarials directly into a vein (intravenously, or IV) if you are unable to take oral medication. IV delivery is also used when the malaria infection has progressed and may lead to permanent complications or when the infection has become life-threatening. In the United States, quinidine gluconate is the medication of choice in these situations.

Antimalarials to prevent recurrences

Some people have recurring flu-like symptoms for years after the initial malarial infection. Relapses from infection of P. vivax or P. ovale are the most common and can be prevented by taking primaquine.

What To Think About

• Children who weigh less than 33 lb (15 kg)should not visit an area that has a risk of chloroquine-resistant malaria.
• How effective medicines are in preventing and treating malaria depends on the medication resistance of the parasites in the geographic location where the malaria infection occurs.
• If you are going to a location where malaria is present, it is very important to take preventive medicines and to follow the correct schedule for taking them. The majority of people who become infected with malaria did not take preventive malaria medicines or did not follow the correct dosing schedule.
• Pregnant women should discuss medication options with their doctor.

There is no surgical treatment for malaria.

Exchange blood transfusions

Exchange blood transfusions may be considered for treating severe cases of malaria if:

• The percentage of blood cells infected with the parasite (parasite density) is greater than 5%.
• You have altered mental capacity (severe confusion) due to the malaria infection.
• You have lung or kidney complications.

Exchange blood transfusion is the quickest way to remove parasites. This procedure involves withdrawing blood from you at the same time that donor blood is being injected. During this exchange, the amount of blood in your body stays constant. Quinidine gluconate is given by needle into a vein (intravenously) at the same time as the blood transfusion. Parasite density is checked every 12 hours until it is less than 1%.

Organizations

Citations

1. Schapira A (2004). Malaria. In DL Heymann, ed., Control of Communicable Diseases Manual, 18th ed., pp. 324–340. Washington, DC: American Public Health Association.

2. American Academy of Pediatrics (2006). Malaria. In LK Pickering et al., eds., Red Book: 2006 Report of the Committee on Infectious Diseases, 27th ed., pp. 435–441. Elk Grove Village, IL: American Academy of Pediatrics.

3. Baird JK, Hoffman SL (1999). Prevention of malaria in travelers. Medical Clinics of North America, 83(4): 923–944.

4. Croft AM (2006). Malaria: Prevention in travellers. Clinical Evidence (15): 1088–1106.

5. Suh KN, et al. (2004). Malaria. Canadian Medical Association Journal, 170(11): 1693–1702.

6. Centers for Disease Control and Prevention (2004). Treatment of malaria (Guidelines for clinicians). Available online: http://www.cdc.gov/malaria/pdf/clinicalguidance.pdf.

Other Works Consulted

• Prevention of malaria (2000). Medical Letter on Drugs and Therapeutics, 42(1070): 8–9.

• Kain KC, et al. (2001). Malaria chemoprophylaxis in the age of drug resistance. I. Currently recommended drug regimens. Clinical Infectious Diseases, 33(2): 226–234.

• Martens P, Hall L (2000). Malaria on the move: Human population movement and malaria transmission. Emerging Infectious Diseases, 6(2): 103–109.

• Taylor TE, Strickland GT (2000). Malaria. In GT Strickland, ed., Hunter's Tropical Medicine and Emerging Infectious Diseases, 8th ed., pp. 614–643. Philadelphia: W.B. Saunders.