Malaria: Causes, Symptoms, and Treatment

Medically Reviewed by Zilpah Sheikh, MD on March 18, 2024
12 min read

Malaria is a serious and sometimes life-threatening disease. It spreads through bites from infected mosquitos.

Malaria is not common in the U.S. But you can get it when you travel to other parts of the world. 

About 2,000-2,500 people are diagnosed with malaria per year in the U.S. But these people are mostly travelers returning from countries where malaria is more common, which includes countries south of the Sahara desert in Africa as well as parts of South America and Southeast Asia. These countries have climates hot enough for the mosquitoes that carry the malaria parasite (anopheles mosquitos) to thrive.

About 608,000 people die from malaria in 85 countries each year. People in countries that have access to medication, such as the U.S., are less likely to be infected and to die of malaria.

In the U.S., it's rare to get malaria. However, as of September 2023, nine people (seven in Florida, one in Texas, and one in Maryland) were diagnosed with malaria; doctors thought they got infected in the U.S. Experts think someone who traveled to one of those countries brought the parasite to the U.S. Then a local mosquito bit that person and spread malaria to other people.

There are ways to prevent malaria. Before you travel, check the CDC’s website to see if your destination is a place where malaria spreads. You may have to take pills before, during, and after your trip to lower your chances of getting it.

Malaria is caused by a group of parasites called plasmodium. These parasites are carried by female anopheles mosquitos. You get infected when an infected mosquito bites you and injects the parasites into your bloodstream.

Several species of plasmodium can cause malaria in humans, including:

Plasmodium falciparum (P. falciparum). This is the species that causes the most severe form of malaria. P. falciparum can multiply fast in your blood and cause anemia from serious blood loss and clogs in your small blood vessels. Clogs in the small blood vessels of your brain can cause a potentially life-threatening complication called cerebral malaria. This species can be found worldwide in tropical and subtropical areas, but it's especially common in Africa.

P. vivax. This species can live in your liver and cause a relapse months or years after you were bitten by an infected mosquito. It's found mostly in Asia, Latin America, and in some parts of Africa.

P. ovale. This species is very similar to P. vivax, but it can't infect people who have a specific blood group called the Duffy blood group. It's found mostly in Africa (especially West Africa) and the islands of the western Pacific.

P. malariae. When left untreated, this species can cause a long-lasting, chronic infection that can last a lifetime. In some people, this can cause a serious complication where you lose a lot of protein in your pee. This species is found throughout the world.

P. knowlesi. This species mostly infects a couple of monkey species: long-tailed and pig-tailed macaques. However, researchers have recently found that it can infect humans too. P. knowlesi has a short, 24-hour reproductive cycle, so it can become a severe infection fast. In some cases, the infected person can even die. This species is found throughout Southeast Asia.

Most people get infected with plasmodium parasites when they are bitten by a mosquito that's infected.

It's very rare, but in some cases, it can also spread through:

  • Blood transfusions or organ transplants from people who were infected (However, most blood and organs are tested before use, so this is extremely rare.)
  • Sharing needles or syringes contaminated with malaria-infected blood
  • An infected pregnant person passing it to their unborn infant before or during delivery

Is malaria contagious?

Malaria isn’t contagious because it doesn't spread from one person to another like colds or the flu. Also, you can't catch it through casual or close contact or by having sex with someone who has the infection. In general, you have to be bitten by an infected mosquito to get it.

Malaria life cycle

A mosquito is infected when they bite, or take a blood meal, from a person who's infected. About a week after it bites an infected person, it will have parasites in its spit that will be injected into the next person it bites. So, plasmodium infection is a cycle that goes from mosquito to human and back again.

Once the parasites enter your body, they travel to your liver, where they multiply. They get into your red blood cells and lay their eggs. When their eggs hatch after about a week, new parasites flood into that red blood cell until it bursts. This releases more parasites into your bloodstream, infecting more of your red blood cells. As they get into more of your healthy red blood cells, you may become very sick.

Anyone can get malaria, but about 3.3 billion people, or half of the world's population, are at risk for malaria. 

Most people who are infected live in countries with widespread malaria. But people from countries with no or little malaria can still be infected when they travel to countries with malaria. Malaria is most common in places with mostly warm weather, such as:

  • Africa, particularly areas that are south of the Sahara desert
  • South and Southeast Asia
  • Areas around the eastern Mediterranean, from Turkey to northern Africa and eastward to Iran
  • Central and South America
  • Australia, New Zealand, and other islands in the western Pacific

If you live in a place with high malaria rates, you may become partially immune to it. This means your symptoms may not be as serious if you get it. But your immunity can go down if you move to a place with less malaria.

Some people have a higher risk of getting a serious case of malaria. These include:

  • Children and babies
  • People who have HIV or AIDS
  • Pregnant people
  • Travelers who live in areas without malaria

Symptoms usually start about 10-15 days after you're bitten by an infected mosquito. Symptoms can include:

Malaria symptoms can be similar to cold or flu symptoms, so it might be hard to tell what you have at first. Malaria symptoms don’t always show up within 2 weeks, especially if it’s a P. vivax infection.

Malaria can get serious quickly, so it’s important to get medical care as soon as possible. If you think you may have gotten malaria while traveling in an area where it's common, go see a doctor. The CDC has a traveler's information page that can help you understand how to prevent malaria infection and where to go for medical help while you're traveling. You can also ask your doctor about taking malaria medication with you on your travels, especially if you are at high risk of infection. Early treatment can help prevent serious complications.

Symptoms of serious malaria include:

  • Impaired consciousness
  • Convulsions
  • Difficulty breathing
  • Serious tiredness and fatigue
  • Dark or bloody urine
  • Yellow eyes and skin (jaundice)
  • Abnormal bleeding

If you have any of these symptoms, go to the ER right away.

Your doctor may suspect malaria based on your travel history, symptoms, and physical exam. To confirm that you have it, your doctor may order some laboratory tests, which can tell your doctor:

  • If the parasite is in your blood
  • If certain medications will work against the parasite
  • If your body has ever made antibodies to fight off malaria 

Malaria tests

Your doctor may order any or a few of the following laboratory tests, including:

Blood smear. This is the most common and accurate malaria test. A lab technician, doctor, or nurse will take some of your blood and send it to a lab. The technician will use a special stain on it to make any parasites show clearly, then they will spread it on a glass slide and look at it under a microscope. They will usually do a thick smear to diagnose malaria and a thin smear to see which malaria species you are infected with and how many of your red blood cells are infected.

The number of malaria parasites in your blood can be low at first. So your test might say you don’t have malaria even when you do. For that reason, you may need three blood tests over 2 or 3 days for the most accurate results.

Rapid diagnostic test (RDT). Also called antigen testing, this is a quick option when blood draws and smears aren't available. Antigens are proteins your body makes to "tag" foreign invaders so your immune system knows to attack and kill them. These tests work in a similar way as a home COVID-19 test; your doctor will take blood from a prick on your finger and put it on a test strip that shows a line if you have malaria. However, it may not be able to tell which species of malaria you are infected with or how many parasites you have in your blood, so your doctor will still need to do a blood smear.

Molecular test. Also known as the polymerase chain reaction (PCR) test, this test shows if malaria parasite DNA is in your blood. Your doctor may use this test to confirm the species of parasite you're infected with after a blood smear or an RDT. This can help your doctor decide which medicine to prescribe you.

Antibody test. Doctors use this to find out if you've had malaria before. It shows antibodies, which are proteins your immune system makes if you have been exposed to malaria before.

Drug resistance test. Some malaria parasites are resistant to medicines that doctors use to treat the infection. So, the CDC suggests that doctors test to see which drugs will work on your infection.

Other blood tests. You may also have blood taken for a blood count and chemistry panel. This can tell your doctor how serious your infection is and if it's causing other problems, such as anemia or kidney failure.

The treatment your doctor suggests will depend on a few different factors, such as:

  • The species of parasite you have
  • How bad your symptoms are
  • The geographic area where you got infected (which gives your doctor a clue about what medicines will work for your infection)
  • If you've ever taken an antimalarial medicine before (including whether you've had medicine to prevent malaria infection)
  • Your age (adult or child)
  • Whether you’re pregnant

Malaria medications

Some medications your doctor may prescribe include:

Chloroquine or hydroxychloroquine. This is the medicine your doctor will likely suggest if your infection is caused by chloroquine-sensitive P. falciparum, P. malariae, or P. knowlesi and your symptoms aren’t serious. Areas with chloroquine-sensitive malaria strains include Central America west of the Panama Canal, Haiti, and the Dominican Republic.

Artemether-lumefantrine (Coartem) or atovaquone-proguanil (Malarone). Your doctor may prescribe one of these if your infection is caused by P. falciparum that is resistant to chloroquine or for children who weigh less than about 11 pounds (5 kilograms).

Quinine sulfate plus doxycycline, tetracycline, or clindamycin. This is another treatment option for infections caused by P. falciparum or P. vivax that is resistant to chloroquine.

Primaquine phosphate. This medicine can be added to chloroquine or hydroxychloroquine if your infection is caused by chloroquine-resistant P. vivax or P. ovale. It can kill the forms of these species that live in your liver and cause you to relapse.

Mefloquine. This is another option if your infection is caused by P. vivax that is resistant to chloroquine. However, this medicine isn't used unless you can't take any other medicines because of the risk of serious side effects in your brain. Strains that are found in Southeast Asia are resistant to this medicine.

Artesunate. If your symptoms are serious, your doctor may give you this drug by IV for the first 24 hours. After you get it, they may follow up with 3 days of artemisinin-based combination therapy. 

Quinidine gluconate. This is another option for people with serious infections. Depending on how serious your symptoms are, your doctor may also give you clindamycin, doxycycline, or tetracycline by IV.

Serious health problems that can come with malaria include:

  • Coma
  • Cerebral malaria (brain damage caused by swelling)
  • Pulmonary edema
  • Liver, kidney, and spleen failure
  • Anemia (when you lose too many red blood cells)
  • Very low blood sugar

You can get malaria again after you've had it. Some species of the parasite cause a milder form of illness that can last a long time and come back in the future.

If you travel to an area where malaria spreads, here are some ways to prevent an infection:

Wear clothes that can protect your skin. Wear long pants, long-sleeved shirts, and a hat to cover your skin. Tuck in your clothes so that none of your skin is exposed. For added protection, spray permethrin on your clothes.

Wear insect repellent. Spray or spread it on any areas of skin your clothes don't cover. The U.S. Environmental Protection Agency (EPA) recommends products with these ingredients:

  • DEET
  • Picaridin (called icaridin or KBR 3023 outside the U.S.)
  • IR3535
  • Oil of lemon eucalyptus (OLE) -- but do not use this on children younger than 3 years
  • Para-menthane-3,8-diol (PMD) -- but do not use this on children younger than 3 years
  • 2-undecanone 

Check the U.S. EPA's search tool to help you find the right repellent.

Layer your sun protection. If you use sunscreen, put that on first. Then, put on a bug repellent.

Use a bed net. If the place you're staying in doesn't have window and door screens, put a net over your bed to protect you from bites when you sleep. Spray the net with an insecticide such as permethrin for added protection.

Take a preventive medicine. Your doctor can prescribe medicines such as chloroquine, primaquine, or Malarone. Which drug your doctor suggests depends on where you are going, and if you're on any medicines that might interact with it. You take the drug before you go, while you're there, and after you get home. 

Write down the drug's brand and generic names, and keep that with you while you travel. Leave the medicine in its original package.

Avoid travel in some cases. Try to avoid travel to areas with malaria if you're pregnant. Malaria can cause pregnancy problems such as miscarriage and early delivery. If you have to go on the trip, take preventive medicine and avoid mosquito bites.

The CDC has resources online to help you know what to do if you travel to a country with malaria. You can also learn what types of parasites are there and what medicines you can take to prevent malaria.

Travel smart. Enroll your trip with the Department of State’s Smart Traveler Enrollment Program (STEP). Once you're enrolled, the U.S. government can track if you have any medical issues while traveling. STEP also has a list of companies that offer travel medical insurance.

The World Health Organization (WHO) recommends the RTS,S/AS01 and R21/Matrix-M vaccines to prevent malaria in children who live in areas where P. falciparum spreads. They can lower the rate of serious and life-threatening malaria infections.

The WHO recommends the vaccines for children starting at around 5 months old. Children get the vaccines in four doses. In areas with a high risk of malaria, children can also get a fifth dose.

Experts have found that the vaccine has had major public health benefits. Almost 2 million children in some parts of Africa have already received the RTS,S/AS01 vaccine as part of studies. Vaccination has led to a 13% drop in child deaths from malaria in those areas.

There have been some challenges in getting the vaccines to all the children who need them. Health experts say it will take more than just vaccines to control malaria. Insecticide sprays and nets are also important.

Malaria spreads through the bite of infected female anopheles mosquitoes. The parasite that causes malaria lives in warm-weather climates such as Africa, South Asia, and Central and South America. If you travel to an area where malaria spreads, take anti-malaria medicine, cover your skin with clothing, and use an insect repellant. If you do get malaria, see a doctor quickly for treatment to prevent complications.