You get malaria from the bite of an infected female Anopheles mosquito. The mosquito injects microscopic parasites into your bloodstream while feeding, and those parasites then travel to your liver and red blood cells where they multiply and cause illness. Malaria killed an estimated 597,000 people worldwide in 2023, with 263 million total cases that year.
The Mosquito Bite That Starts It All
Only female Anopheles mosquitoes transmit malaria, and only when they’re already carrying the parasite from a previous blood meal on an infected person. When an infected mosquito bites you, it injects saliva that contains the parasite’s “sporozoite” stage, a tiny, needle-shaped form designed specifically to invade your liver. Not every Anopheles mosquito carries malaria. The mosquito has to have previously bitten someone who was already infected, picking up the parasite and allowing it to develop inside the mosquito’s gut before it can pass the infection along.
Anopheles mosquitoes tend to bite between dusk and dawn. They breed in standing water, which is why malaria thrives in tropical and subtropical climates with warm temperatures and rainy seasons. The WHO African Region carries the greatest burden: just 11 countries account for roughly two thirds of all global cases and deaths.
What the Parasite Does Inside Your Body
Once the parasites enter your bloodstream, they don’t immediately make you sick. They travel to your liver first, quietly invading liver cells and multiplying over the course of days. Inside those cells, each parasite produces thousands of copies of itself. When the liver cell eventually bursts open, all those copies flood into your bloodstream and begin invading red blood cells.
Inside red blood cells, the parasites feed, grow, and multiply again. When a red blood cell is packed full, it ruptures, releasing a new wave of parasites that go on to infect more red blood cells. This cycle of invasion, multiplication, and rupture is what produces malaria’s hallmark pattern of fever, chills, and sweating. Each wave of bursting red blood cells triggers a new spike of symptoms.
Two species of the malaria parasite can also leave behind dormant forms in the liver called hypnozoites. These sleeper cells can reactivate weeks, months, or even years later, causing a relapse long after the original infection seemed to be over. This is why some travelers develop malaria symptoms well after returning home from a trip.
Five Parasite Species That Infect Humans
Malaria isn’t caused by a single parasite. Five species of the Plasmodium parasite infect humans:
- P. falciparum is the deadliest and most common in sub-Saharan Africa. It causes the most severe illness and is responsible for the vast majority of malaria deaths.
- P. vivax is the most widespread species outside Africa and can leave dormant liver stages that cause relapses.
- P. ovale also produces dormant liver forms and is found primarily in West Africa.
- P. malariae causes a milder form of malaria but can persist in the blood at low levels for years if untreated.
- P. knowlesi is a monkey malaria parasite found in Southeast Asia that occasionally jumps to humans.
Which species you’re exposed to depends largely on where in the world the bite happens.
Transmission Without a Mosquito Bite
In rare cases, malaria spreads without a mosquito being involved at all. Because the parasite lives inside red blood cells, anything that transfers infected blood from one person to another can transmit the disease. Known routes include blood transfusions, organ transplants, and sharing needles or syringes contaminated with infected blood.
A pregnant person with malaria can also pass the infection to their baby before or during delivery. This is called congenital malaria. It’s uncommon but serious, since newborns have no immunity to the parasite.
How Long Before You Feel Sick
The incubation period, the gap between the mosquito bite and the first symptoms, typically ranges from 7 to 30 days. P. falciparum tends toward the shorter end of that window, while P. malariae leans toward the longer end. If you’ve been taking antimalarial prevention medication, the appearance of symptoms can be delayed by weeks or even months. Combined with the dormant liver stages of P. vivax and P. ovale, this means malaria can show up long after you’ve left an area where transmission occurs.
Early symptoms often mimic the flu: fever, chills, headache, muscle aches, and fatigue. The classic pattern is cyclical fevers that spike every 48 or 72 hours, corresponding to waves of red blood cells bursting. Not everyone develops this textbook pattern, though, especially early in the infection. Severe malaria caused by P. falciparum can progress to organ damage, severe anemia, or neurological complications if not treated promptly.
Who Is Most at Risk
Your risk depends almost entirely on exposure to infected mosquitoes. People living in or traveling to tropical regions, particularly sub-Saharan Africa, South and Southeast Asia, Central and South America, and parts of the Pacific Islands, face the highest risk. Within those regions, risk increases during and just after rainy seasons, when mosquito populations surge.
Young children and pregnant people in endemic areas are especially vulnerable because their immune systems either haven’t encountered the parasite before or are naturally suppressed during pregnancy. People who grow up in high-transmission areas develop partial immunity over years of repeated exposure, which is why malaria in adults in these regions is often less severe. That partial immunity fades if you move away for several years, which is why people visiting their home countries after living abroad can be caught off guard.
Travelers from non-endemic countries have zero natural immunity, making even a single bite from an infected mosquito potentially dangerous. Preventive medication, insecticide-treated bed nets, and mosquito repellent are the primary tools for reducing your chances of infection when visiting areas where malaria is present.