Malaria is caused by parasites that enter your body through the bite of an infected mosquito. This sometimes fatal disease happens in hot and humid places, like Africa.
Plasmodium species infection causes malaria. Fever (which may be intermittent), chills, rigors, sweating, diarrhea, stomach discomfort, respiratory distress, disorientation, seizures, hemolytic anemia, splenomegaly, and renal abnormalities are some of the symptoms and indications of this condition. Rapid diagnostic assays and the detection of Plasmodium in a peripheral blood smear are used for diagnosis. Depending on the Plasmodium species, medication sensitivity, and clinical condition of the patient, treatment and prevention are prescribed. The fastest acting regimen for treating acute disease is the fixed combination of atovaquone and proguanil. Less often used regimens for treating acute disease include chloroquine, quinine, or mefloquine. Primaquine or a single dose of tafenoquine are also given to patients with P. vivax and P. ovale infections to avoid recurrence.
How common is malaria?
Malaria is common in tropical areas where it’s hot and humid. In 2020, there were 241 million reported cases of malaria throughout the world, with 627,000 deaths due to malaria. The majority of these cases occur in Africa and South Asia.
A mosquito gets infected when it bites a person who has malaria. The parasite the mosquito carries enters the bloodstream of the person it bites. The parasites grow there. Humans can contract one of five different kinds of malaria parasites.
In certain instances, women who are pregnant and have malaria may pass the illness to their unborn children.
While improbable, malaria can spread through hypodermic needles, organ transplants, and blood transfusions.
The Plasmodium species that infect humans are
- P. falciparum
- P. vivax
- P. ovale
- P. malariae
- P. knowlesi
Concurrent infection with more than one Plasmodium species is uncommon but can occur.
P. knowlesi is a pathogen in Southeast Asia, particularly in Malaysia. Macaque monkeys are the primary hosts. P. knowlesi is usually acquired by people living or working near or in forests.
The basic elements of the life cycle are the same for all Plasmodium species. Transmission begins when a female Anopheles mosquito feeds on a person with malaria and ingests blood containing gametocytes.
During the following 1 to 2 weeks, gametocytes inside the mosquito reproduce sexually and produce infective sporozoites. When the mosquito feeds on another human, sporozoites are inoculated and quickly reach the liver and infect hepatocytes.
The parasites mature into tissue schizonts within hepatocytes. Each schizont produces 10,000 to 30,000 merozoites, which are released into the bloodstream 1 to 3 weeks later when the hepatocyte ruptures. Each merozoite can invade a red blood cell (RBC) and there transform into a trophozoite.
Signs and symptoms of malaria are similar to flu symptoms. They include:
- Fever and sweating.
- Chills that shake your whole body.
- Headache and muscle aches.
- Chest pain, breathing problems and cough.
- Diarrhea, nausea and vomiting.
As malaria gets worse, it can cause anemia and jaundice (yellowing of the skin and whites of the eyes).
The most severe form of malaria, which may progress to a coma, is known as cerebral malaria. This type represents about 15% of deaths in children and nearly 20% of adult deaths.
The incubation period is usually
- 12 to 17 days for P. vivax
- 9 to 14 days for P. falciparum
- 16 to 18 days or longer for P. ovale
- About 1 month (18 to 40 days) or longer (years) for P. malariae
However, some strains of P. vivax in temperate climates may not cause clinical illness for months to > 1 year after infection.
Manifestations common to all forms of malaria include
- Fever and rigors—the malarial paroxysm
Malarial paroxysm is caused by hemolysis of infected RBCs, released merozoites and other malaria antigens, and the inflammatory response they elicit. The classic paroxysm starts with malaise, abrupt chills and fever rising to 39 to 41° C, rapid and thready pulse, polyuria, headache, myalgia, and nausea. After 2 to 6 hours, fever falls, and profuse sweating occurs for 2 to 3 hours, followed by extreme fatigue. Fever is often hectic at the start of infection. In established infections, malarial paroxysms typically occur every 2 to 3 days depending on the species.
- Light microscopy of blood (thin and thick smears)
- Rapid diagnostic tests that detect Plasmodium antigens or enzymes in blood
Fever and chills in an immigrant or traveler returning from an endemic region should prompt immediate assessment for malaria. Symptoms usually appear in the first 6 months after infection, but onset may take up to 2 years or, rarely, longer.
Malaria can be diagnosed by finding parasites on microscopic examination of thick or thin blood smears. The infecting species (which determines therapy and prognosis) is identified by characteristic features on smears (see table Diagnostic Features of Plasmodium Species in Blood Smears ). If the initial blood smear is negative, additional smears should be repeated at 12- to 24-hour intervals until 3 smears are negative.
Thin blood smears stained with Wright-Giemsa stain allow assessment of parasite morphology within red blood cells (RBCs), often speciation, and determination of percentage parasitemia (parasite density), evaluated using oil immersion magnification of portions of the smear where RBCs are more or less touching, which should show about 400 RBCs per field. Thick smears are more sensitive but more difficult to prepare and interpret as the RBCs are lysed before staining. Sensitivity and accuracy of the results depend on the examiner’s experience.
Diagnostic Features of Plasmodium Species in Blood Smears
|Characteristic||Plasmodium vivax*||Plasmodium falciparum||Plasmodium malariae†|
|Infected red blood cells (RBCs) enlarged||Yes||No||No|
|Maurer dots or clefts||No||Yes§||No|
|Multiple infections in RBCs||Rare||Yes||No|
|Rings with 2 chromatin dots||Rare||Frequent||No|
|Bayonet or band trophozoites||No||No||Yes|
|Schizonts present in peripheral blood||Yes||Rare||Yes|
|Number of merozoites per schizont (mean [range])||16 (12–24)||12 (8–24)¶||8 (6–12)|
|* Red blood cells (RBCs) infected with P. ovale are fimbriated, oval, and slightly enlarged; the parasites otherwise resemble P. vivax.|
|† P. knowlesi is morphologically similar to P. malaria and has been confused with it. P. knowlesi should be considered in patients with malaria acquired in Southeast Asia, particularly in Malaysia.|
|‡ Schüffner dots are best seen when the blood smear is stained with Giemsa stain.|
|§ This feature is not always visible.|
|¶ Schizonts are trapped in viscera and usually are not present in peripheral blood.|
It’s important to start treating malaria as soon as possible. Your provider will prescribe medications to kill the malaria parasite. Some parasites are resistant to malaria drugs.
Some drugs are given in combination with other drugs. The type of parasite will determine what type of medication you take and how long you take it.
Antimalarial drugs include:
- Artemisinin drugs (artemether and artesunate). The best treatment for Plasmodium falciparum malaria, if available, is artemisinin combination therapy.
- Atovaquone (Mepron®).
- Chloroquine. There are parasites that are resistant to this medication.
- Doxycycline (Doxy-100®, Monodox®, Oracea®).
Medications can cure you of malaria.
If you plan on living temporarily in or traveling to an area where malaria is common, talk to your provider about taking medications to prevent malaria. You will need to take the drugs before, during and after your stay. Medications can greatly reduce the chances of getting malaria. These drugs can’t be used for treatment if you do develop malaria despite taking them.
You should also take precautions to avoid mosquito bites. To lower your chances of getting malaria, you should:
- Apply mosquito repellent with DEET (diethyltoluamide) to exposed skin.
- Drape mosquito netting over beds.
- Put screens on windows and doors.
- Treat clothing, mosquito nets, tents, sleeping bags and other fabrics with an insect repellent called permethrin.
- Wear long pants and long sleeves to cover your skin.
Is there a vaccine against malaria?
There’s a vaccine for children which was developed and tested in Ghana, Kenya and Malawi in a pilot program. The RTS, S/AS01 vaccine is effective against Plasmodium falciparum malaria, which causes severe disease in children.