Paris -- Following Are Facts About Malaria: What is it? A life-threatening parasitic disease transmitted by mosquitoes that rivals HIV/AIDS as the world's worst health problem.

Its name -- "mal aria"-- comes from the former belief that the disease came from breathing in fetid air from stagnant marshes. In 1880, scientists isolated a one-cell parasite called a plasmodium that is the real cause of Malaria. The disease occurs in poor tropical countries that are home to 40 percent of the world's population. It was eliminated from countries with more temperate climates by the middle of the 20th century, AFP reported.

The toll: Malaria kills over a million people a year, or about 3,000 a day. Ninety percent of cases are in sub-Saharan Africa. At least 300 million people suffer from acute malaria each year, often suffering lasting effects. Children aged under five, pregnant women and their unborn children and the elderly are the most vulnerable.

Symptoms: Fever, headache, vomiting and other flu-like symptoms appear about nine to 14 days after the parasite is passed on, the duration varying according to the type of plasmodium. Drugs are then needed to treat the symptoms and kill the parasites. Malaria can kill by destroying red blood cells, causing anemia, or clog the blood capillaries that provide oxygen to the brain, a condition called cerebral malaria. The most lethal of the four parasite strains is plasmodium falciparum.

How is it spread: Via a female mosquito of the anopheles gambiae strain, which feeds almost exclusively on human blood and hands on the parasite in its saliva when it takes a blood meal. Once inside the body, the parasite undergoes through several complex changes as part of its life cycle. It evades the immune system, infects the liver and red blood cells and finally develops into a form that is able to infect a mosquito again when it bites an infected person.

Treatment: As yet, there is no cure or vaccine for malaria.

Swift use of drugs to treat symptoms and kill the parasites in an infected person can significantly reduce the death toll. The cheapest drug, chloroquine, is rapidly losing its effectiveness because the P. falciparum parasite is becoming resistant to it.

Prevention: Draining stagnant pools and water butts, where mosquitoes breed, and using insecticide-treated mosquito bed netting can prevent more than half malaria transmission in high-risk areas.

Economic cost: Malaria costs Africa more than 12 billion dollars a year. The continent's gross domestic product would be a third greater today if malaria had been eliminated in the sixties, using DDT. That insecticide was withdrawn because it is a dangerously accumulative pollutant.