Malaria is caused by parasites from the genus Plasmodium, which are spread to people by infected mosquitoes. There are five species of Plasmodium that can infect humans.
Statistics show that there are 250 million to 500 million cases of malaria each year in the world, causing up to 1 million deaths. Deaths are more common in children.
Although North America, Western Europe, and Russia are free of malaria, transmission still occurs in many other tropical and subtropical countries of the world. Disease rates are highest in sub-Saharan Africa.
The hallmark of malaria is fever. Initially, symptoms may mimic the flu. Fever may be accompanied by shaking chills and muscle aches. Anemia is common.
Severe cases may cause organ failure or death.
Causes of Malaria
Malaria is caused by protozoan of the genus Plasmodium. There are several stages in the life cycle of Plasmodium, including sporozoites, merozoites, and gametocytes. Sporozoites are the form that is injected by the mosquito into humans. Infection begins with a bite from an infected mosquito. After being injected into the human host by the mosquito, the parasite travels into the bloodstream and eventually makes its way to the liver, where the parasite begins to reproduce and develop into merozoites. The merozoites leave the liver and enter red blood cells to reproduce. Soon, new parasites burst out in search of new red blood cells to infect.
Sometimes, the reproducing Plasmodia will create a form known as a gametocyte in the human bloodstream, which is infectious to mosquitoes. If a mosquito takes a blood meal when gametocytes are present, the parasite begins to reproduce in the insect and create sporozite forms that are infectious to people, completing the life cycle.
There are five species of Plasmodium that infect humans:
P. vivax: Though it is most common in India and Central and South America, it’s found worldwide. Infections can sometimes lead to life-threatening rupture of the spleen. This type of malaria can hide in the liver and return later to cause a relapse years after the first infection. Special medications are used to eradicate P. vivax from the liver.
P. ovale: It is rarely found outside Africa. Symptoms are similar to those of P. vivax. Like P. vivax, P. ovale can hide in the liver for years before bursting out again to cause symptoms.
P. malariae: It’s found worldwide but is less common than the other forms. This form of malaria is hard to diagnose because there are usually very few parasites in the blood. If untreated, the infection can last many years.
P. falciparum: This is the most life-threatening species of malaria. Although present throughout much of the tropical and subtropical world, it is particularly common in sub-Saharan Africa. P. falciparum is resistant to many of the older drugs used to treat or prevent malaria.
P. knowlesi: Found in Malaysia, this species can cause high levels of parasites in the blood, leading to organ failure or death.
Common symptoms of malaria
In the early stages, malaria symptoms are sometimes similar to those of many other infections caused by bacteria, viruses, or parasites.
Symptoms may include:
Nausea and vomiting
Symptoms may appear in cycles and may come and go at different intensities and for different lengths of time. But, especially at the beginning of the illness, the symptoms may not follow this typical pattern.
The cyclic pattern of malaria symptoms is due to the life cycle of malaria parasites camera as they develop, reproduce, and are released from the red blood cells and liver cells in the human body. This cycle of symptoms is also one of the major indicators that you are infected with malaria.
Other common symptoms of malaria include:
Dry (nonproductive) cough
Muscle and/or back pain
In rare cases, malaria can lead to impaired function of the brain or spinal cord, seizures, or loss of consciousness.
Infection with the P. falciparum parasite is usually more serious and may become life-threatening.
Many diseases cause fever in the tropical and subtropical world, including malaria, tuberculosis, yellow fever, dengue fever, typhoid, and cholera. Each of these is managed differently. Thus it is very important to make a specific diagnosis.
Malaria is diagnosed by seeing the parasite under the microscope. Blood taken from the patient is smeared on a slide for examination. Special stains are used to help highlight the parasite. Sometimes, it is possible to identify the species of Plasmodium by the shape of the parasite, especially if gametocytes are seen. Whenever possible, smears should be reviewed by someone with expertise in the diagnosis of malaria. If the smears are negative, they can be repeated every 12 hours. Smears that are repeatedly negative suggest another diagnosis.
Two types of other tests are available for diagnosis of malaria. Rapid tests can detect proteins called antigens that are present in Plasmodium. These tests take less than 30 minutes to perform. However, the Food and Drug Administration and the Centers for Disease Control and Prevention recommend that these new tests be used in conjunction with microscopy. A second type of test that is newly available is the polymerase chain reaction (PCR), which detects malaria DNA. Because this test is not widely available, it is important not to delay treatment while waiting for results.
Malaria caused by P. falciparum may come back (reocur) at irregular intervals for up to 2 years if treatment is not complete.
Malaria caused by P. vivax and P. ovale may reocur at irregular intervals for up to 3 to 4 years, but medicine can prevent relapses.
P. malariae can remain in the blood of an infected person for more than 30 years, usually without causing any symptoms.
Factors that increase your risk of getting malaria include:
Living or traveling in a country or region where malaria is present.
Traveling in an area where malaria is common and:
Not taking medicine to prevent malaria before, during, and after travel, or failing to take the medicine correctly.
Being outdoors, especially in rural areas, between dusk and dawn (nighttime), when the mosquitoes that transmit malaria are most active.
Not taking steps to protect yourself from mosquito bites.
Your risk of getting malaria depends on your age, history of exposure to malaria, and whether you are pregnant. Most adults who have lived in areas where malaria is present have developed partial immunity to malaria because of previous infections and so almost never develop severe disease. But young children who live in these areas and travelers to these areas are especially at risk for malaria because they have not developed this immunity.
Pregnant women are more likely than non-pregnant women to get severe malaria, because the immune system is suppressed during pregnancy.
In addition, pregnant women, young children, older adults, and people with other health problems are more likely to have serious complications if they get malaria.
Complications of malaria
Malaria is a very serious illness which can be fatal if not diagnosed and treated quickly.
The falciparum parasite causes the most severe malaria symptoms and most deaths.
The destruction of red blood cells by the malaria parasite can cause severe anaemia.
Anaemia is a condition where the red blood cells are unable to carry enough oxygen to the body’s muscles and organs, leaving you feeling drowsy, weak and faint.
Some rare cases of malaria can affect the brain. This is known as cerebral malaria and it can cause your brain to swell, sometimes leading to permanent brain damage. It can also cause seizures (fits) or coma (a state of unconsciousness).
Other complications that can arise due to severe malaria include:
- breathing problems, such as fluid in your lungs
- liver failure and jaundice (yellowing of the skin and whites of the eyes)
- shock (a sudden drop in blood flow)
- spontaneous bleeding
- abnormally low blood sugar
- kidney failure
- swelling and rupturing of the spleen
- dehydration (a lack of water in the body)
As complications of severe malaria can occur within hours or days of the first symptoms, it is important to seek urgent medical help as soon as possible.
The effects of malaria are usually more severe in pregnant women, babies, young children and the elderly.
Malaria in Pregnancy
Malaria in pregnancy is a major cause of maternal morbidity worldwide and leads to poor birth outcomes. Pregnant women are more prone to complications of malaria infection than nongravid women. Treatment involves antimalarial drugs and supportive measures. Prevention involves chemoprophylaxis and mosquito avoidance.
Record has it that each year, 50 million women living in malaria-endemic areas become pregnant; one-half of these women live in Africa. It is estimated that 10,000 women and 200,000 infants die as a result of malaria infection during pregnancy; severe maternal anemia, prematurity, and low birth weight contribute to more than half of these deaths.
Malaria in pregnancy increases the risk of:
- maternal anaemia
- spontaneous abortion
- low birth weight
- neonatal death
WHO recommends a package of interventions for the prevention and control of malaria during pregnancy.
- The use of insecticide treated nets (ITNs) to prevent infection;
- Intermittent Preventive Treatment (IPT) to prevent asymptomatic infections among pregnant women living in areas of moderate or high transmission of P. falciparum;
- Effective case management for malaria illness and anaemia.
Malaria in pregnancy is dangerous for both the mother and the fetus. Therefore, pregnant women with malaria must be treated promptly with an effective antimalarial agent to clear parasites rapidly. Safety and efficacy data to guide management are limited . In general, the newer the drug, the more likely it is to be effective (in part because there has been insufficient time for resistance to emerge), but fewer data will be available on safety in pregnancy. Clinicians therefore have to make treatment decisions based on the clinical severity of infection, epidemiologic resistance patterns, and available data regarding safety of the drug or class of drug in pregnancy.
P. falciparum — Pregnant women with severe P. falciparum malaria should receive parenteral therapy; the intravenous route is preferred over the intramuscular route. Options for therapy include artesunate or quinine (plus clindamycin) . In nonpregnant adults and children with severe malaria, a mortality benefit has been demonstrated with artesunate over quinine. No trials have compared the efficacy of these agents in pregnant women.
Malaria in infants
Of the estimated one million annual deaths from malaria, approximately 80% occur in young African children.
Infants are vulnerable to malaria from approximately 3 months of age, when immunity acquired from the mother starts to wane.
In areas of intense malaria transmission, most cases of severe malarial anaemia, blood transfusions, and deaths occur in infants and young children. Severe anaemia probably accounts for more than half of all childhood deaths from malaria in Africa, with case fatality rates in hospital of between 8-18%.
Prevention is clearly of critical importance, and the targeted delivery of interventions to prevent malaria and anaemia in high-risk groups (pregnant women, infants and young children) would be an appropriate use of limited financial and human resources.
To prevent malaria, there is the need to avoid mosquito bites.
Guidelines to prevent mosquito bites include:
Stay inside when it is dark outside, preferably in a screened or air-conditioned room.
Wear protective clothing (long pants and long-sleeved shirts).
Use insect repellent with DEET (N,N diethylmetatoluamide). The repellent is available in varying strengths up to 100%. In young children, use a preparation containing less than 24% strength, because too much of the chemical can be absorbed through the skin.
Use bed nets (mosquito netting) sprayed with or soaked in an insecticide such as permethrin or deltamethrin.
Use flying-insect spray indoors around sleeping areas.
Avoid areas where malaria and mosquitoes are present if you are at higher risk (for example, if you are pregnant, very young, or very old).
Other steps that may be helpful in reducing the risk of malaria include using air conditioning and electric fans, wearing protective clothing, using aerosol insecticides in your house, and taking certain antimalarial medicines.
Compiled by Temitope Obayendo with additional materials from emedicinehealth; bodyandhealth.canada and www.who.int