The vast majority of Americans who get malaria pick it up while traveling abroad. In 2022, the CDC recorded 1,999 confirmed malaria cases in the United States, and 93.5% of them were contracted during international travel. The parasite doesn’t circulate in the US under normal conditions, so getting malaria almost always means being bitten by an infected mosquito somewhere else in the world, then returning home with the parasite already multiplying inside your body.
The Mosquito Bite: How Infection Actually Works
Malaria spreads through the bite of a female Anopheles mosquito carrying Plasmodium parasites. When the mosquito feeds on your blood, it injects microscopic parasites called sporozoites into your skin. These travel through your bloodstream to your liver, where they quietly replicate inside liver cells. After multiplying, they burst out as a new form of the parasite and flood into your red blood cells. That’s when you start feeling sick.
The whole process from bite to first symptoms typically takes 7 to 30 days, depending on which species of parasite you were infected with. The most dangerous species tends to cause symptoms on the shorter end of that range, while other species can take weeks or, in rare cases, lie dormant in the liver for months before flaring up.
Where Travelers Get Infected
Africa dominates the map. Among imported cases in 2022, 90.2% of travelers had been to Africa. Asia accounted for 4.3%, Central America and the Caribbean for 2.9%, and South America for 2.3%. Regions like Oceania and the Middle East made up less than 1% combined.
Sub-Saharan Africa carries the highest risk because the mosquito species there are especially efficient at transmitting the parasite, malaria is widespread year-round in many areas, and the most dangerous parasite species is dominant across the continent. A two-week trip to visit family in Nigeria or Ghana carries far more malaria risk than a comparable trip to Southeast Asia, though both regions require precautions.
Why “Visiting Friends and Relatives” Travelers Are Hit Hardest
A disproportionate number of US malaria cases occur in immigrants and their children who travel back to their home countries to visit family. These travelers often skip preventive medication because they assume they’re still immune from having grown up around malaria. That assumption is dangerous. Immunity to malaria fades after you move to a country without it, sometimes within just a few years. The CDC has documented deaths among these travelers after they returned to the United States.
Unlike tourists staying at resort hotels, people visiting relatives often stay in homes without air conditioning or window screens, in rural or suburban areas where mosquito exposure is higher. They also tend to stay longer, which increases the odds of being bitten by an infected mosquito.
Local Transmission Inside the US
It’s rare, but it can happen. In the summer of 2023, eight cases of locally acquired malaria were reported in Florida (seven cases in Sarasota County) and Texas (one case in Cameron County). None of these patients had traveled internationally. This was the first local transmission documented in the US since 2003.
The pattern in both states followed a similar chain: someone returned from abroad carrying the parasite, a local Anopheles mosquito bit that person, picked up the parasite, and then bit someone else nearby. All seven Florida cases occurred within a four-mile radius. A separate locally acquired case involving a more dangerous parasite species was diagnosed in Maryland later that same summer. These events are considered public health emergencies precisely because they’re so unusual, and local health departments responded with intensive mosquito control.
Rarer Ways It Can Happen
Mosquito bites account for nearly all malaria transmission, but a few other routes exist. The parasite can be transmitted through blood transfusions, organ transplants, and shared needles. Plasmodium parasites survive in stored blood at refrigerator temperatures for up to 18 days and can remain detectable in frozen blood for nearly a month. Transfusion-transmitted malaria is especially concerning because parasites enter the bloodstream directly, bypassing the liver stage, which can lead to severe illness before anyone suspects malaria as the cause.
There’s also a phenomenon called “airport malaria” or “odyssean malaria,” where an infected Anopheles mosquito hitches a ride on an aircraft from an endemic country and bites someone at or near the destination airport. Cases have been documented in Europe. It’s exceedingly rare but serves as a reminder that malaria can occasionally reach people who never left home and never received a transfusion.
A pregnant person with malaria can also pass the parasite to their baby, known as congenital malaria.
What Malaria Feels Like and How Dangerous It Is
Initial symptoms resemble a bad flu: fever, chills, sweating, headache, body aches, and fatigue. Because these symptoms are so generic, malaria is frequently misdiagnosed or overlooked in American emergency rooms, where doctors may not immediately think of it. If you’ve traveled to a malaria-endemic area in the past few months and develop a fever, mention your travel history explicitly.
Severity depends heavily on which parasite species is involved. The most dangerous species, Plasmodium falciparum, caused severe illness in about 9.3% of US cases and death in 0.9% over a 26-year study period. The milder species, Plasmodium vivax, caused severe illness in 1.3% and death in 0.09%. Those numbers have been climbing in recent years. Between 2008 and 2011, the rate of severe illness from falciparum rose to 21%, likely because of delayed diagnosis rather than a more dangerous parasite. In 2022 alone, 10 people in the US died of malaria.
How It’s Diagnosed in the US
The gold standard is a microscopic examination of your blood. A technician spreads a drop of blood on a glass slide, stains it, and looks for parasites inside your red blood cells under high magnification. This method identifies both the species and how heavily infected you are, which directly guides treatment decisions.
A rapid diagnostic test can deliver results in about 15 minutes by detecting parasite proteins in a blood sample. One such test is FDA-approved for use in US clinical laboratories. If either test is positive, a more advanced molecular test (PCR) is often run to confirm exactly which species is present.
Preventing Malaria as a Traveler
Preventive medication is the most reliable protection. Several options are available, and they differ mainly in how far in advance you need to start them and how long you continue after returning home. Some are taken daily, others weekly. The daily options typically start one to two days before travel and continue for 7 days after you leave the endemic area. The weekly options start one to two weeks before departure and must be continued for four weeks after you return. Your doctor will choose based on which region you’re visiting, since parasite resistance to certain drugs varies by geography.
No antimalarial drug is 100% effective, so combining medication with mosquito avoidance is important. Sleep under insecticide-treated bed nets, use repellent containing DEET or picaridin, and wear long sleeves and pants during peak biting hours, which for Anopheles mosquitoes means dusk through dawn. Staying in air-conditioned or well-screened rooms makes a significant difference.
The critical mistake many travelers make is stopping their medication early after returning home because they feel fine. The parasite can still be developing in your liver during those final days of the regimen. Completing the full course is what prevents a case of malaria from showing up weeks after you’ve unpacked your suitcase.