Malaria

Malaria is caused by a bite from an infected mosquito, which injects a number of germs called Plasmodium (about 20 per bite) into the bloodstream. There are four different Plasmodium - called falciparum, vivax, ovale and malariae. These are all members of the protozoa family, other members of which cause trypanosomiasis and leishmaniasis, described above. Once the Plasmodium are in the bloodstream, they move to the liver and multiply to produce many thousands of immature forms called merozoites, which invade red blood cells and multiply further before rupturing the cells and entering the bloodstream. The mosquito which bites an infected person takes up the germs as it feeds. The germs pass into that mosquito’s stomach and multiply, and then pass to the salivary glands and are injected into the next person when the mosquito bites, thereby spreading the disease.

The time taken for reproduction and release of the parasites in the blood varies between 48 and 72 hours, depending on the type of Plasmodium, and the release causes a rise in temperature often accompanied by violent shaking (called a rigor) followed by profuse sweating. The most severe form, caused by plasmodium falciparum, may cause continuously elevated temperature and be complicated by the development of cerebral malaria, when the parasites invade the brain, low blood sugar and kidney failure. The presence of large amounts of haemoglobin in the urine gives rise to the term Blackwater Fever.

Malaria is a major and increasing problem in many parts of the world, causing millions of deaths - particularly in young children. There is resistance developing to many of the treatments that have been used, particularly chloroquine, and intending travellers to countries where malaria is a risk need to seek up-to-date advice about prophylaxis. This should ideally be taken from three weeks before travelling (because some treatments cause side-effects, and it’s better to find out before you get there) and continued for four weeks after you return, because of the time period of incubation. The main methods of prevention, however, depend on preventing the bites in the first place using effective insect repellents, nets at night (the time when the mosquitoes bite) and long-sleeved shirts and long trousers.
 
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