Is Malaria Contagious? Understanding the Transmission

Each year, nearly 300 million malaria infections occur globally and more than 400,000 people die. Infection in the U.S. is very unlikely, but every year, the U.S. reports approximately 2,000 cases of malaria, most of which are among people who traveled to an area where malaria is spread by mosquitoes.

What is malaria?

Like dengue fever and West Nile Virus, malaria is an illness caused when a person is bitten by a mosquito carrying a one-celled parasite belonging to the genus Plasmodium. Four species of this genus can cause illness in humans if transmitted. The species that can cause the most severe illness is Plasmodium falciparum (P. falciparum).

Symptoms of malaria

The symptoms of malaria vary widely from no symptoms or mild illness to flu-like symptoms, such as fever and chills, as well as more severe illness and death if treatment is not provided. The most common symptoms are:

  • Headache
  • Muscle ache
  • Fatigue
  • Fever
  • Chills
  • Nausea
  • Vomiting
  • Diarrhea
  • Neurological issues (dizziness, confusion, disorientation, or coma)

Signs of serious illness include severe anemia, respiratory distress, and organ failure.

Dengue symptoms are similar to malaria but also include a skin rash, and severe dengue infection can cause hemorrhagic fever or dengue shock syndrome.

West Nile Virus infections tend not to cause symptoms of illness for the majority of infected, but those who do feel ill may experience body aches, vomiting, and diarrhea.

Is malaria contagious?

Malaria is not contagious because it is not passed directly from human to human.

Mosquitoes are the carriers, thus, if a mosquito bites an infected person, the mosquito can carry it to a susceptible person.

How is malaria transmitted?

Malaria is transmitted when an infected female Anopheles mosquito bites a susceptible person. If an uninfected Anopheles mosquito bites a person with malaria, the mosquito can become infected and carry the illness to another person.

The female Anopheles mosquito carries the Plasmodium parasite as a part of the parasite's life cycle, but the parasite does not cause any notable damage to the mosquito. However, when the parasite enters the human host, another part of its life cycle begins. During this cycle, Plasmodium can cause a very mild illness or flu-like illness in humans, which may result in more serious complications.

Malaria is more likely to be spread during the warmer, wetter months when mosquitoes are active and laying eggs. Traveling during the cooler, drier months may help to reduce the risk of malaria infection.

Can you get malaria more than once?

Yes, you can contract malaria more than once because immunity declines quickly. People who grew up in a place where malaria is prevalent may believe that they are immune, but they should take the same precautions as other travelers.

How is malaria diagnosed?

A blood sample is examined under a microscope, ideally within 24 hours of seeking medical attention. This is a 'gold standard' for malaria testing. People who are not immune to malaria can have symptoms even if the blood smear does not detect the parasite at first. Blood smears should be repeated every 12–24 hours until three negative results have been obtained.

The blood smear analysis also helps the clinician estimate the spread of the parasite by checking how many red blood cells are infected by it. Rapid tests are approved in the U.S. as well, but these can only determine whether a person has malaria or not and require subsequent confirmatory testing for the diagnosis. The rapid tests are unable to estimate the spread of the parasite or identify specific species of Plasmodium, nor are they as sensitive as a blood smear, so malaria cases can be missed.

Polymerase chain reaction (PCR) testing is also available and useful for identifying the specific species of parasite. This knowledge is helpful because some species are resistant to specific drugs. The Centers for Disease Control and Prevention (CDC) offers free-of-charge drug-resistance testing for malaria in the U.S.

Preventing malaria

To prevent contracting malaria, the first step is to be aware of the countries where exposure is likely, such as West Africa and Oceania. Travelers should be mindful that prevention of malaria requires preparation and the willingness to adopt a multi-layered approach.

When traveling to an area with limited malaria transmission, taking precautions to avoid mosquito bites may be enough. In areas with the highest risk of infection, preventive treatments may also be advised.

Drugs to prevent malaria

There are several drugs that can prevent malaria, but no drug treatment is 100% protective. The type of drug recommended varies by country, so be sure to check the list. The drugs available are listed in alphabetical order with no correlation to effectiveness.

Seek a consultation with a travel medicine physician to fully explore your options depending on the area you are traveling to, the season (colder, drier months tend to have less transmission), your activities (business travel in hotels or adventuring), evening activities (dining and entertainment), and whether you may have already contracted malaria in the past.

Travelers at higher risk for infection

First- and second-generation immigrants who are living in a non-endemic area and return to their country of origin where malaria is more prevalent account for half of all the annual U.S. cases of malaria.

The risk of infection among travelers visiting friends and relatives may be higher for various reasons, such as a longer trip, more outdoor or evening activities, and potentially staying in homes that are not fully screened. While no special or unusual precautions are required, the CDC recommends drug prophylaxis.

Pregnant women are also at higher risk because the infection can be more severe and increase the risk of pregnancy complications. The risks may include premature birth, pregnancy loss, and stillbirth. The CDC recommends considering the importance and timing of travel to reduce the risk.

Reducing exposure to mosquitoes

The Anopheles mosquito tends to bite in the late evening and night. When traveling or living in an area where malaria is endemic, follow these precautions:

  1. Wear loose-fitting clothing to cover the arms and legs
  2. Close windows and doors (or repair windows, doors, and screens)
  3. Use air conditioners to keep mosquitoes out
  4. Use a bug spray approved by the Environmental Protection Agency (EPA)
  5. Remove areas with standing water to reduce opportunities for mosquitoes to lay eggs

Treatment for malaria

If you develop flu-like symptoms while traveling or living in a country with mosquito-borne infections, seek medical care and testing. Treatment should be started when malaria is confirmed because the specific drug selected depends on the parasite species. Treatment recommendations published by the CDC consider whether a person was already taking anti-malarial drugs for prevention, in which case a different drug or combination of drugs should be used.

Patients can be started on oral treatment unless their disease is very severe, such as loss of consciousness, anemia, acute kidney injury, respiratory distress, or circulatory collapse. In these severe cases, intravenous treatment may be recommended.

Malaria vaccination and its availability

The World Health Organization (WHO) has recommended a second malaria vaccine (R21). The first vaccine approved in 2021 was RTS,S/AS01, under the brand name Mosquirix. These vaccines are administered in a three-dose series to young children before the age of 2 and must be given just before the peak spread of malaria.

Symptomatic cases of malaria were reduced by 75% by the more recent vaccine R21 during the 12 months after vaccination. No literature exists to date that compares one vaccine to the other. This vaccine is recommended by the WHO for widespread use among children living in sub-Saharan Africa and other areas with moderate or high transmission, but no vaccine is available in the U.S. yet.

Creating a vaccine against malaria is extremely challenging because the human immune response is complex, as is the life cycle of the parasite. The parasite produces many antigens, and immunity seems to wane quickly. People who were previously infected can become reinfected, and the parasite can lay dormant for months without causing symptoms.

Partial protection in those with sickle cell trait

The human toll of malaria infection is so heavy that it is proposed to have impacted the genetic make-up of populations living in malaria-endemic areas such as sub-Saharan Africa. For instance, 80% of people who have a specific gene causing sickle cell trait live in sub-Saharan Africa where the deadliest species of parasite (P. falciparum) is carried by mosquitoes.

Although people with two copies of the gene causing sickle-shaped hemoglobin can have serious complications, those who have only one faulty copy are partially protected against P. falciparum. The precise reason this mutation is partially protective is not fully understood.

Overall, malaria is a serious condition that needs immediate medical attention once symptoms are noted. While it is not contagious, nor can it be passed from human to human, preventative measures should always be taken when traveling to minimize infection risk.

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