Malaria is a mosquito-borne parasitic infection spread by Anopheles mosquitoes. The Plasmodium parasite that causes malaria is neither a virus nor a bacterium – it is a single-celled parasite that multiplies in red blood cells of humans as well as in the mosquito intestine.
When the female mosquito feeds on an infected person, male and female forms of the parasite are ingested along with human blood. The male and female forms of the parasite meet and mate in the mosquito's gut, and the infective forms are passed onto another human when the mosquito feeds again.
Malaria is a significant global problem. In 2015, there were 214 million cases of the disease worldwide, killing about 438,000 people. Malaria is prevalent in Africa, Asia, the Middle East, Central South America, Hispaniola (Haiti and the Dominican Republic), and Oceania (Papua New Guinea, Irian Jaya, and the Solomon Islands). In Canada, malaria is most often caused by travel to and from endemic areas.
Each year, up to 1 million Canadians travel to malaria-endemic areas. This results in 350 to 1,000 annual cases of malaria in Canada and 1 to 2 deaths per year.
The parasite has progressively developed resistance to many anti-malarial medications, and in several areas of the world, especially southeast Asia, resistance to all anti-malarial drugs has been reported.
There are 4 species of the Plasmodium parasite that can cause malaria in humans: P. falciparum, P. vivax, P. ovale, and P. malariae. The first 2 types are the most common. Plasmodium falciparum is the most dangerous of these parasites; infection with it can kill rapidly (within several days), whereas the other species cause illness but usually not death. Falciparum malaria is particularly frequent in sub-Saharan Africa and Oceania.
You can only get malaria if you're bitten by an infected mosquito or if you receive infected blood from someone during a blood transfusion. Malaria can also be transmitted from mother to fetus during pregnancy.
The mosquitoes that carry Plasmodium parasite get it from biting a person or animal that's already been infected. The parasite then goes through various changes that enable it to infect the next creature the mosquito bites. Once it's in you, it multiplies in the liver and changes again, getting ready to infect the next mosquito that bites you. It then enters the bloodstream and invades red blood cells. Eventually, the infected red blood cells burst. This sends the parasites throughout the body and causes symptoms of malaria.
Malaria has been with us long enough to have changed our genes. The reason many people of African descent suffer from the blood disease sickle cell anemia is that the gene that causes it also confers some immunity to malaria. In Africa, people with a sickle cell gene are more likely to survive and have children. The same is true of thalassemia, a hereditary disease found in people of Mediterranean, Asian, or African American descent. (See the article on "Anemia" for more information.)
Symptoms and Complications
Symptoms usually appear about 1 to 3 weeks after infection. People with malaria will have many but not generally all of the following symptoms:
- abdominal pain
- chills and sweats
- diarrhea, nausea, and vomiting (these symptoms only appear sometimes)
- high fevers
- low blood pressure causing dizziness if moving from a lying or sitting position to a standing position (also called orthostatic hypotension)
- muscle aches
- poor appetite
In people infected with P. falciparum, the following symptoms may also occur:
- anemia caused by the destruction of infected red blood cells
- extreme tiredness, delirium, unconsciousness, convulsions, and coma
- kidney failure
- pulmonary edema (a serious condition where fluid builds up in the lungs, which can lead to severe breathing problems)
P. vivax and P. ovale can lie dormant in the liver for up to a year before causing symptoms. They can then remain dormant in the liver again and cause later relapses. P. vivax is the most common type in North America.
Making the Diagnosis
You may have malaria if you have any fever during or after travel in malarial regions. See a doctor quickly, and get your blood tested to check if the parasite is present. The doctor will also check to see if you have an enlarged spleen, which sometimes accompanies the fever of malaria. Don't wait to get home for treatment if you get malaria abroad.
Plasmodium parasites in the blood are usually visible under the microscope. There are also simple dipstick tests (done by dipping a piece of paper with chemicals on it into your blood) that can be used to identify P. falciparum. Blood tests as well as liver and kidney function tests will be done to check the effects of the parasite on your body.
Treatment and Prevention
If recognized early, malaria infection can be completely cured. Depending on the severity of your symptoms, you may be treated as an outpatient. The medication chosen by your doctor depends on:
- the type of malaria (knowing the species of parasite will help your doctor choose the most appropriate medication for you or determine whether hospitalization is necessary)
- the area you travelled to or visited when you contracted malaria (the doctor needs to know this because in certain geographical locations the malaria is resistant to some medications)
- the severity of the illness
- your medical history
- if you are pregnant
Treatment usually lasts for 3 to 7 days, depending on the medication type. To get rid of the parasite, it's important to take the medication for the full length of time prescribed – don't stop taking the medication even if you feel better. If you experience any side effects, your doctor can recommend ways to manage them or may choose to give you a different medication.
If you're travelling to a malarial region, you should take a course of preventive treatment. Medications similar to those used to cure malaria can prevent it if taken before, during, and after your trip. It's vital to take your medication as prescribed, even after you return home.
Before travelling, check with your doctor or travel clinic about the region's malaria status. Risk of infection also depends on:
- altitude (lower altitudes have higher risk)
- camping vs. hotel stay
- length of stay
- rural vs. urban areas (rural areas have higher risk)
- season (infection is more common during the rainy season)
- time of day (night is worse)
Since mosquitoes are night feeders, stay away from danger zones – particularly fields, forests, and swamps – from dusk to dawn to avoid being bitten. Use permethrin-treated mosquito netting when sleeping. Using mosquito coils and aerosolized insecticides containing pyrethroids may also help improve protection during this time.
Wear long sleeves and pants, and light-coloured clothing. Put mosquito repellent containing DEET on exposed skin. Use products containing up to 30% DEET for adults and children over 12 years – higher concentrations can have serious side effects, especially in children. Children 12 years old and younger should use products containing 10% DEET or less. Do not apply more than 3 times a day on children 2 to 12 years old. For children aged 6 months to 2 years, apply no more than once a day of a product containing 10% or less of DEET. DEET and sunscreen combinations are not recommended. If sunscreen is needed, apply the sunscreen first, wait 20 minutes, and then apply DEET.