Malaria
A parasitic disease caused by four species of PLASMODIUM: P. falciparum, P. vivax, P. ovale, and P. malariae. It causes recurrent episodes of high fever, sometimes associated with RIGOR; enlargement of the SPLEEN is common. P. falciparum infection can also be associated with several serious - often fatal - complications (see below): although other species cause chronic disease, death is unusual.
During a bite by the female mosquito, one or more sporozoites - a stage in the life-cycle of the parasite - are injected into the human circulation and taken up by liver cells, where they divide further into merozoites. These are liberated into the bloodstream where they invade red blood cells and again divide, releasing further merozoites. As merozoites are periodically liberated into the bloodstream, they cause the characteristic fevers, rigors, etc.
Malaria occurs in many tropical and subtropical countries; P. falciparum is, however, confined very largely to Africa, Asia and South America. It is a significant problem for travellers, who should obtain sound advice on prevention before embarking on tropical trips -especially to a rural area where intense transmission can occur (see www.netdoctor.co.uk/diseases/facts/malaria.htm).
Frequent international air travel has exposed many more people to the risk of malaria, and infected individuals may not have symptoms until they have returned home. Doctors seeing a recent traveller with unexplained pyrexia and illness should consider the possibility of malarial infection. Transmission has also been recorded at airports in Western countries, and following blood transfusion. The resurgence of malaria has been worldwide, partly because of resistant strains of the disease, and partly because many countries have failed (or been unable) to implement environmental measures to eliminate mosquitoes. According to the World Health Organisation,around 300-500 million people a year contract malaria with about 2-3 million deaths - as many as 70 per cent of them being children under the age of 5. The apparently steady increase of global warming means that countries with temperate climates may well warm up sufficiently to enable malaria to become established as an ENDEMIC disease.
Diagnosis is by demonstration of trophozoites - a further stage in the parasite's life-cycle - in blood-films.
Gross SPLENOMEGALY (hyper-reactive malarious splenomegaly, or tropical splenomegaly syndrome) can complicate all four human Plasmodium spp. infections.
infections cause less severe disease than P. falciparum (see below). Acute complications are unusual, but chronic ANAEMIA is often present.
Complications of P. falciparum infection include brain involvement (see BRAIN - Cerebrum), due to adhesion of immature trophozoites to the lining of brain blood cells. Renal involvement (frequently resulting from HAEMOGLOBINURIA), PULMONARY OEDEMA, HYPOTENSION, HYPOGLYCAEMIA, and complications in pregnancy are also important. In complicated disease, HAEMODIALYSIS and exchange TRANSFUSION have been used.
usually produces a chronic infection, and chronic renal disease (nephrotic syndrome) is an occasional sequel, especially in tropical Africa.
Malaria specialists in the United Kingdom have produced guidance for residents travelling to endemic areas for short stays. Drug choice takes account of:
risk of exposure to malaria;
extent of drug resistance;
efficacy of recommended drugs and their side-effects;
criteria relevant to the individual (e.g. age, pregnancy, kidney or liver impairment).
Personal protection against being bitten by mosquitoes is essential. Permethrin-impregnated nets are an effective barrier, while skin barrier protection and vaporised insecticides are helpful. Lotions, sprays or roll-on applicators all containing diethyltoluamide (DEET), are safe and effective when put on the skin. Their effect, however, lasts only for a few hours. Long sleeves and trousers should be worn after dark.
Drug prophylaxis should be started at least a week before travelling into countries where malaria is endemic (two or three weeks in the case of mefloquine), and should be continued for at least four weeks after leaving endemic areas. Even if all recommended antimalarial programmes are followed, it is possible that malaria may occur any time up to three months afterwards. Medical advice should be sought if any illness develops. Chloroquine can be used as a prophylactic drug where the risk of resistant falciparum malaria is low; otherwise, mefloquine or proguanil hydrochloride should be used. Travellers to malaria-infested areas should seek expert advice on appropriate prophylactic treatment well before departing.
Various chemoprophylactic regimes are used. Where the infecting species is P. falciparum or unknown or is mixed, initial treatment is with quinine, Malarone® (proguanil and atovaquone) or Riamet® (artemether and lumefantrine). If the patient is very ill or unable to swallow, the quinine is given intravenously. In pregnancy the safest combination is quinine and clindamycin. The other more benign types of malaria can usually be managed with less aggressive treatment, such as oral chloroquine. Infection with P. vivax and ovale may also need primaquine to prevent relapse from remaining liver parasites.
Recommendations may change from year to year as the parasite changes its resistance patterns, so up-to-date advice is essential. Research into malarial vaccines is well advanced, much of it financed by over $165 million from the Bill & Melinda Gates Foundation.
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