A parasitic infection of red blood cells spread by mosquitoes
- Visiting or living in areas where the disease occurs are risk factors
- Age, gender, and genetics are not significant factors
Malaria, a parasitic infection that leads to the destruction of red blood cells, is one of the greatest public health problems in the world. In tropical countries, where the infection is most likely to be contracted, about 250 million new cases of malaria and 1 million deaths due to the disease occur every year. Most of those who die of malaria are children. The disease is the most serious health threat to people who visit the tropics. In the UK, there are about 2,000 cases every year, occurring in travellers returning from malaria-endemic areas.
The World Health Organization has been trying to control malaria for years but with only partial success. Malarial parasites are transmitted to humans by mosquitoes of the anopheles group, which have now become resistant to many insecticides. In many areas, the malarial parasite itself has now also become resistant to the common antimalarial drugs. Currently, no effective vaccine has been developed.
If you live in a region where malaria is common, you may have several mild episodes of infection that increase your resistance, making you less likely to develop a serious infection. However, this protection is lost within a year if you move to a malaria-free region. Therefore, if you emigrate from a malaria-affected area and later return for a holiday, you will need to take preventive measures (see Preventing malaria). If you become ill after a visit to the tropics, you should tell your doctor where you have been and when you went there.
What are the types?
The characteristics of malaria have been known for over 2,000 years. However, the cause of the disease was only identified in 1880. Four species of protozoal parasites from the plasmodium group cause malaria in humans, each species causing a different type of malaria. The most dangerous type of malaria is falciparum malaria, caused by Plasmodium falciparum. This type of malaria results in the most deaths and is often fatal within 48 hours of the first symptoms if it is left untreated. The other three types of malaria, caused by Plasmodium malariae, Plasmodium ovale, and Plasmodium vivax, are less severe.
All types of malarial parasite are transmitted to humans by a bite from an infected mosquito. Initially, the parasites multiply in the liver and are then released into the bloodstream, where they penetrate red blood cells. After 48–72 hours, depending on the species of parasite, the infected cells rupture, releasing parasites that invade other red blood cells. If a noninfected mosquito bites the infected person, the insect itself becomes infected and can then spread the disease to other people. In all types of malaria, the disease can pass from an infected pregnant woman to her fetus.
What are the symptoms?
The symptoms of malaria usually begin between 10 days and 6 weeks after being bitten by an infected mosquito. However, in some cases, symptoms may not develop for months or years, especially if preventive drugs were being taken at the time of infection.
If not treated, malaria due to P. vivax, P. ovale, and P. malariae causes recurrent attacks of symptoms with each episode of red blood cell destruction by the parasites. Each attack usually lasts for 4–8 hours and may occur at intervals of 2 or 3 days, depending on the species of parasite. Symptoms of an attack include:
Shivering and chills.
Tiredness, headache, and muscle pain.
Between each attack, extreme tiredness may be the only symptom.
Falciparum malaria causes a continuous fever that may be mistaken for influenza. It is more severe than the other types, and attacks may lead to loss of consciousness and kidney failure and may be fatal.
What might be done?
Your doctor may suspect malaria if you have an unexplained fever within a year after a trip to a region where the infection occurs. Diagnosis is confirmed by identifying the malarial parasite in a blood smear under a microscope, or by a blood test that detects malaria antigens (substances that trigger an immune response) in the blood.
If you are diagnosed with malaria, you should be given antimalarial drugs as early as possible to avoid complications. Treatment depends on the type of malaria, how resistant the parasite is to drugs, and the severity of the symptoms. If you have falciparum malaria, you may be treated in hospital with oral or intravenous antimalarial drugs. Treatment may also involve a blood transfusion to replace destroyed red blood cells or kidney dialysis if kidney function is impaired. Other types of malaria are usually treated on an outpatient basis with oral antimalarial drugs.
If treated early, the outlook is usually good, and most people make a full recovery. However, malaria caused by P. vivax and P. ovale may recur after treatment.
Preventive measures, including using antimalarial drugs, should be taken to reduce the risk of infection when visiting areas where malaria occurs.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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