Malaria is a life-threatening disease caused by microscopic parasites called Plasmodium that are transmitted to people through the bites of infected Anopheles mosquitoes. Five different species of the Plasmodium parasite can infect humans. The parasites develop for weeks to months in the liver and then start to multiply within red blood cells, causing symptoms including fever, headache, vomiting, joint pain, and anemia. If untreated, severe malaria can cause renal failure, coma and death. In chronic malaria, the disease can relapse months or years after exposure due to the presence of latent parasites in the liver.
Approximately half of the world's population is at risk of malaria. Each year, there are approximately 250 million cases of malaria, causing nearly one million deaths, mostly among children and pregnant women in sub-Saharan Africa. Although the majority of cases are in Africa and Asia, malaria is also present in the Americas where it is responsible for 1 million disease cases a year.
Malaria was once common in the United States but was eliminated by 1951 through widespread vector control programs, including widespread DDT application, draining of wetlands, and monitoring and treating infected people. In 1955, the World Health Organization launched an effort to eradicate malaria worldwide. The disease was successfully eradicated from some countries with temperate climates and seasonal malaria transmission, including parts of southern Europe, North Africa and the Middle East. However, other countries saw only modest improvements and still others were completely excluded from the program, including most of sub-Saharan Africa. Eventually, the malaria parasites developed resistance to commonly used drugs, most notably chloroquine, and the mosquito vectors became resistant to many insecticides. In time, the goal of the program switched from eradication to control.
Modern malaria control efforts focus on vector control and efforts to prevent mosquito bites by distributing insecticide-treated bed nets and insect repellents, and spraying insecticides inside houses (indoor residual spraying). Many malaria vaccines are under development, but to date, none has been found that provides a high level of protection for a sustained period.
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