Malaria

(Tropical Diseases, Parasitic Infection)

The Facts

Malaria is a mosquito-borne parasitic infection spread by Anopheles mosquitoes. The Plasmodium parasite that causes malaria is neither a virus nor a bacteria – 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 infectious forms are passed onto another human when the mosquito feeds again.

Malaria is a significant global problem. In 2022, there were 249 million cases of the disease worldwide, killing about 600,000 people. Since 2000, deaths from malaria have decreased by 60%. 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. A very small number of cases come from blood transfusions or are transmitted from local mosquitoes that pass the disease on from returning travellers.

Each year, up to 1 million Canadians travel to malaria-endemic areas. This results in 400 to 500 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. P. vivax is the most common, and 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.

The Causes

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 parent 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 offers some immunity against 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 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)
headache
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
yellowing of the skin or whites or the eyes (also called jaundice)

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 A 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
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.

For severe cases of malaria caused by P. falciparum, treatment may require intravenous injections. These are only available at designated medical centres and pharmacies operated by the Canadian Malaria Network.

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, and place screens on doors and windows. 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 can be safely worn at the same time. Apply the sunscreen first, wait 20 minutes, and then apply DEET. Be sure to wash your hands after application.

There are several vaccines that are used to prevent malaria (RTS,S and R21), and the World Health Organization recommends the large-scale use of these vaccines for children living in areas with moderate-to-high malaria transmission. These vaccines are not approved in Canada but may be available in endemic countries.