Malaria is an infectious disease caused by a parasite that’s transmitted by mosquitoes. The illness results in recurrent attacks of chills and fever, and it can be deadly. Malaria has been virtually eradicated in countries with temperate climates, but it’s still prevalent in tropical and subtropical countries in Africa, Asia, the Middle East, South America and Central America. Malaria remains one of the world’s leading infectious killers, particularly of children in sub-Saharan Africa.
Evolving strains of drug-resistant parasites and insecticide-resistant mosquitoes continue to make malaria a global health problem.
A one-celled parasite, plasmodium, causes malaria. About 170 species of plasmodium exist, but only four cause malaria in humans:
- P. falciparum. This species, predominant in Africa, produces the most severe symptoms and is responsible for most malaria deaths.
- P. vivax. This species, found mostly in tropical areas of Asia, produces less severe symptoms but can remain in your liver and cause relapses for up to four years.
- P. malariae. This species, found in Africa, can cause typical malaria symptoms, but on rare occasions it can remain in your bloodstream for years without producing symptoms. In these cases, you may pass on the parasite to a mosquito or to another person through a blood transfusion.
- P. ovale. This species is found mostly in West Africa. Although rare, it can also remain in your liver and cause relapses for up to four years.
The process of transmission
The transmitter (vector) of the plasmodium parasite to humans is a female anopheles mosquito. When a mosquito bites a person infected with malaria, it ingests a form of the parasite called gametocytes. The plasmodium completes part of its life cycle inside the mosquito, eventually making its way to the mosquito’s salivary glands. Then, when the mosquito bites you, it injects the parasite into your bloodstream.
The parasite migrates rapidly to your liver, where it infects certain liver cells and develops for a week or so. The liver cells eventually burst, releasing a multiplied form of the infection into your bloodstream. Once in your red blood cells, the parasites reproduce further and some develop into the form that’s available to be ingested by a mosquito (gametocytes), thus renewing the transmission cycle. In some cases of P. vivax or P. ovale infection, a form of the parasite can remain inactive in the liver for extended periods of time. Later, reactivation of the parasite’s life cycle causes a relapse.
Other means of transmission
A pregnant woman can transmit the infection to her unborn baby. Malaria also can be transmitted through blood transfusions. In the United States, steps have been taken to prevent this type of transmission. People who have been in a malaria-endemic area are prohibited from donating blood for a year after returning from such an area, or three years if they’ve been a resident of a malaria-endemic area or have been treated for malaria.
A malaria infection is generally characterized by recurrent attacks with the following signs and symptoms:
- Moderate to severe shaking chills
- High fever
- Profuse sweating as body temperature falls
- General feeling of unease and discomfort (malaise)
Other signs and symptoms include:
Because malaria infection often initially appears to be a flu-like illness or some other viral disease, be wary if you develop an illness with fever while living in a malaria-endemic area or within 12 months after traveling to a high-risk malaria region. See your doctor as soon as possible, and tell your doctor where you’ve traveled. Left untreated, a malaria infection can cause serious, potentially life-threatening health problems.
People who have little or no immunity to malaria are most at risk for serious illness. Residents of a malaria region may acquire some immunity to the disease during their lifetime, but those who haven’t yet acquired immunity are at risk. People at increased risk for serious disease include:
- Young children and infants
- Travelers coming from areas with no malaria
- Pregnant women and their unborn children
Poverty, lack of knowledge, and little or no access to health care also contribute to malaria deaths worldwide.
It’s also possible to lose your immunity if you’re no longer frequently exposed to the parasite. So even if you’ve previously lived in a region where malaria exists, take antimalarial precautions if you return to such an area after an extended period away.
Most serious complications of malaria are associated with infection by P. falciparum. Among the complications are:
- Anemia. This can result from extensive destruction of red blood cells.
- Cerebral malaria. If parasite-filled blood cells block small blood vessels to your brain (cerebral malaria), swelling of your brain or brain damage may occur.
Other complications may include:
- Breathing problems, at times severe in the form of accumulated fluid in your lungs (pulmonary edema)
- Liver failure
- Kidney failure
- Enlarged spleen
If untreated, P. falciparum malaria can be fatal within a matter of hours.
After noting your symptoms and travel history, likely obtain a sample (smear) of your blood for observation under a microscope. Two blood samples, taken at six- and 12-hour intervals, can usually confirm the presence of the malaria parasite and its type.
A malaria infection, particularly with P. falciparum, requires prompt evaluation and treatment. In most cases, doctors can treat malaria effectively with one or more of the following medications:
- Chloroquine (Aralen)
- Quinine sulfate (Qualaquin)
- Hydroxychloroquine (Plaquenil)
- Combination of sulfadoxine and pyrimethamine (Fansidar)
- Mefloquine (Lariam)
- Combination of atovaquone and proguanil (Malarone)
- Doxycycline (Doryx, Vibramycin, others)
- Artemisinin-derived medications. Another class of antimalarial drugs, often prescribed in Asia and now in other parts of the world, is derived from artemisinin, a sweet wormwood extract. Artesunate is an example of an artemisinin derivative.
- Halofantrine. Doctors sometimes use halofantrine to treat malaria, although it’s not marketed in the United States. If you’ve been taking mefloquine for prevention of malaria or if you have heart problems, don’t take halofantrine because it can be dangerous and possibly fatal.
- Primaquine. This drug may be given to fight the dormant liver form of the parasite and prevent relapses. However, the Centers for Disease Control and Prevention (CDC) has warned against taking primaquine if you’re pregnant or have an enzyme deficiency called glucose-6-phosphate dehydrogenase (G6PD) efficiency. Don’t take primaquine until you’ve passed a screening test for G6PD deficiency.
Which drug you take and the length of treatment depend on the type of malaria, where you were infected, your age and how sick you were when treatment began. Drugs are given either orally or intravenously, depending on the severity of illness. In some countries, they may be given in suppository form. After treatment, you may feel very weak and tired for a few weeks.
The problem of drug resistance
The history of antimalarial medicine has been marked by a constant struggle between evolving drug-resistant parasites and the search for new drug formulations. In many parts of the world, for instance, resistance to chloroquine has rendered the drug ineffective.
Currently, anti-malaria experts are focusing on therapies that combine artemisinin derivatives with other companion drugs. These combinations are referred to as artemisinin-based combination therapy (ACT). Artemisinins act quickly in your bloodstream, rapidly clearing away parasites and helping you feel better faster. They may also help reduce transmission of the disease by reducing the number of gametocytes — the infective version of the parasite — in your bloodstream. There’s little documented resistance to artemisinins, and their combination with other drugs may slow resistance to these companion drugs as well. In addition, ACT has few known side effects.
The downside of these combination drugs is that they are often more expensive than conventional antimalarials. Also, doctors must be careful in selecting companion drugs for different geographical regions, in order to avoid administering drugs for which resistance is already present and weakening the effect of the combination therapy.
One of the goals of malaria research is to find companion drugs that haven’t already been used as antimalarials, thus lessening the risk of drug resistance. More research is also needed to prove the safety and effectiveness of combination therapies, particularly with regard to children and pregnant women.
There’s no effective vaccine against malaria. In countries where the disease is endemic, prevention involves keeping mosquitoes away from humans. This includes the use of insecticide-treated mosquito netting and spraying indoor walls with insecticide.
Most drugs used to treat malaria are also used to prevent it. Two or three months before traveling to an area where malaria is prevalent, talk to your doctor or a tropical disease specialist or visit a travel health clinic to obtain the necessary medications to prevent malaria and to receive travel-related vaccines and information. Explain to your doctor exactly where you’re going. The drugs you’re prescribed depend on the level of drug resistance within your area of travel.
For preventive treatment, you generally take the prescribed drug one to two weeks before leaving, throughout your trip, and for four weeks after your return. Some medications may slightly differ from this schedule. For example, Malarone is taken one to two days before you leave and throughout your travels, and for only one week after you return, instead of four weeks. Overdosage of antimalarial drugs can be fatal, so follow your prescription carefully. Don’t miss doses.
In addition, discuss possible and prior adverse reactions to medications. Some have fewer side effects than others. Also, be sure to review your medical history to help identify any possible side effects of taking a medication. For example:
- Mefloquine may infrequently cause nausea, dizziness, insomnia and vivid dreams. In people with past or present psychiatric disorders, mefloquine can worsen symptoms of mental problems.
- Doxycycline can permanently stain the teeth of children younger than 8. It can also cause sun-induced rash. Don’t take doxycycline if you’re pregnant, because it can harm the fetus.
- Malarone is dangerous for people with severe kidney impairment. It’s also generally not prescribed during pregnancy — though, in some cases, it may be — because there is little research on its safety during pregnancy.
If you’re pregnant, avoid traveling to malaria-endemic regions. If this isn’t possible, your doctor can prescribe an antimalarial drug that’s appropriate for you, such as chloroquine or mefloquine (during the second or third trimester). Drug resistance to chloroquine occurs throughout Southeast Asia and Africa, but the drug is still effective for preventing malaria in some areas of Central America, the Middle East and China.
Be careful about purchasing antimalarial drugs in other countries. Quality of drugs varies widely from country to country, depending on the level of regulation and quality control. To avoid questionable products while traveling, the CDC recommends that you:
- Take your medications with you. Purchase medicines in advance in your home country and take them with you.
- Note drug names. Record the generic and brand names of your drugs and the manufacturers, so that if you run out, you can find the correct replacement.
- Inspect packaging. Make sure any drug you purchase is in its original packaging and that the packaging appears authentic.
- Avoid suspicious drugs. Avoid taking tablets that have a strange smell, taste or color, or that are extremely brittle. This may reflect poor storage conditions, which can affect chemical components of the drug.
The CDC also recommends the following measures to help prevent malaria:
- Use repellent. Spray DEET insect repellent, in DEET concentrations up to 50 percent, on exposed skin, and use flying-insect spray to kill mosquitoes in your sleeping area. Choose the concentration based on the hours of protection you need — the higher the concentration of DEET, the longer you are protected. A 10 percent concentration protects you for about two hours. Don’t use DEET on the hands of young children or on infants younger than age 2 months.
- Wear protective clothing. During active mosquito times, usually from dusk to dawn, wear pants and long-sleeved shirts. Apply permethrin, an insecticide, to your clothing and shoes prior to travel. You can also buy clothing pretreated with permethrin. In addition, some stores carry other anti-mosquito supplies, such as hats with attached mosquito netting that protects your face and neck.
- Use netting. If you’re staying in a place that doesn’t have screens or air conditioning, sleep under mosquito netting that’s been treated with permethrin. This netting is available in many travel and camping supply stores and online.