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Malaria
What is it?
Malaria is caused by four species of parasitic, single-celled organisms called protozoa: Plasmodium falciparum, P. vivax, P. malariae and P. ovale.
Malaria parasites have a complex life cycle and need both a human and an Anopheles mosquito host, which picks up the parasite from the blood of an infected human when it feeds. The parasite reproduces in the mosquito’s gut, then passes into human hosts in the mosquito’s saliva.
The four species of parasites cause somewhat different types of disease.
Infection with Plasmodium falciparum malaria — the major type of malaria in Africa, where 90 per cent of cases occur — kills 10 to 40 per cent of untreated children and non-immune adults. P falciparum malaria causes fever, headache and debilitation, and can lead to cerebral malaria (where the brain is infected) or placental malaria, a life-threatening complication of pregnancy.
P. falciparum malaria is highly resistant to drugs and is becoming more common in parts of Africa and in Asia.
P. vivax, P. malariae and P. ovale malaria cause debilitation, chills and fever lasting up to 14 days. These forms of malaria are rarely fatal, but P. vivax and P. ovale malaria can relapse if not properly treated.
Where is it found?
Malaria occurs in most tropical and many subtropical regions. It is most common between 23.5o North (the Tropic of Cancer) and 23.5o South, but cases also occur outside these latitudes in parts of South Africa and around New Delhi in India.
The predominant species in Africa is P. falciparum, the most dangerous of the four. Malaria outbreaks are now being reported in some parts of Africa — for example, the highlands of Kenya — that were previously free from the disease. Malaria has also reappeared in Zanzibar, Madagascar and South Africa.
P. falciparum, vivax and malariae malaria occur in parts of the Middle East and are widespread in India, Pakistan, Bangladesh, Thailand, Vietnam, Laos, Myanmar, Cambodia, Indonesia and Papua New Guinea. P. falciparum resistance is growing throughout Asia.
P. vivax malaria occurs in parts of the Caribbean, Central America (Mexico, Honduras, Nicaragua, Panama, Costa Rica and Guatemala) and South America (Brazil, Peru, Colombia, Bolivia, Ecuador, Venezuela, Guyana, Suriname and French Guiana). P. falciparum cases are growing in many of these countries.
P. vivax malaria occurs in Turkey, Armenia and Azerbaijan.
What are its effects?
Malaria is the most common and deadly parasitic disease in the world, causing an estimated three million deaths a year from direct infection and up to 35 million more (mainly of children and pregnant women) through premature death and disability.
Malaria is an ancient disease but environmental disturbance, malnutrition and the growing failure of drugs once effective in controlling the disease mean malaria is more serious today than it was before control programs were initiated in the 1950s. Up to 500 million people a year will suffer a case of malaria.