malaria

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Infectious parasitic disease of the tropics transmitted by mosquitoes, marked by periodic fever and an enlarged spleen. When a female mosquito of the Anopheles genus bites a human who has malaria, it takes in with the human blood one of four malaria protozoa of the genus Plasmodium. This matures within the insect and is then transferred when the mosquito bites a new victim. Malaria affects around 300–500 million people each year, in 103 countries, and in 1995 around 2.1 million people died of the disease. In sub-Saharan Africa alone between 1.5 and 2 million children die from malaria and its consequences each year. In November 1998, an agreement was reached to establish a multi-agency programme for research and control of the disease. The agencies involved include the World Health Organization (WHO), the World Bank, the United Nations Children's Fund, and the United Nations Development Programme. The Roll Back Malaria campaign aims to halve deaths from malaria by 2010.

Infection
Inside the human body the parasite settles first in the liver, then multiplies to attack the red blood cells. Within the red blood cells the parasites multiply, eventually causing the cells to rupture and other cells to become infected. The cell rupture tends to be synchronized, occurring every 2–3 days, when the symptoms of malaria become evident.

On the increase
Global warming is causing a worldwide increase in malaria. For example, in 1998 in Nairobi, where previously malaria cases had been limited to individuals who had travelled to lowland areas of Kenya, doctors were regularly reporting cases in people who had not left the city. In Irian Jaya, New Guinea, thousands of people who have never been exposed to malaria are now affected. According to a WHO report released in September 1999, cases of malaria in Europe rose from 2,882 in 1981 to 12,328 in 1997. African leaders met in Nigeria in April 2000 to discuss ways of fighting the disease, which was spreading across the continent, and, according to a WHO report, which had cost Africa £160 billion/$100 billion in productivity over the past 35 years.

Treatment
Quinine, the first drug used against malaria, has now been replaced by synthetics, such as chloroquine, used to prevent or treat the disease. However, chloroquine-resistant strains of the main malaria parasite, Plasmodium fulciparum, are spreading rapidly in many parts of the world.

The drug mefloquine (Lariam) is widely prescribed for use in areas where chloroquine-resistant malaria prevails. It is surrounded by controversy, however, as it has been linked to unpleasant side effects, including psychiatric disturbances such as anxiety and hallucinations, epileptic seizures, and memory loss.

Another drug, artemether, derived from the shrub wormwood, was found in 1996 trials to be as effective as quinine in the treatment of cerebral malaria.

The insecticide DDT remains one of the most effective means of controlling malaria, and consequently is still used despite its persistence in the environment and subsequent danger to wildlife.

Vaccine
An experimental malaria vaccine SPf66, developed by Colombian scientist Manuel Patarroyo, was trialled in 1994 in rural Tanzania, where villagers are bitten an average of 300 times a year by infected mosquitoes. It reduced the incidence of malaria by one third. However, further trials of SPf66 in the Gambia concluded that the vaccine provided only 8% protection for young children. A further trial in Thailand in 1996 failed to provide any evidence of its effectiveness. A new vaccine was successfully trialled in rabbits in 1999, with human trials anticipated in 2000. The vaccine attacks Plasmodium falciparum, the parasite that causes the symptoms of the disease, at each stage of the four main stages of its life cycle.

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