Malaria

Malaria is a life-threatening disease caused by Plasmodium parasites that are transmitted to people exclusively through the bites of infected anopheles mosquitoes. These mosquitoes are referred to as malaria vectors; vector used in this context refers to an organism that transfers a pathogen from reservoir to host. There are four types of human malaria:

• Plasmodium falciparum
• Plasmodium vivax
• Plasmodium malariae
• Plasmodium ovale

Malaria is a life-threatening disease caused by parasites that are transmitted to people exclusively through the bites of infected anopheles mosquitoes. Approximately half of the world's population is at risk of malaria, with most malaria cases occurring in sub-Saharan Africa.

Plasmodium falciparum and Plasmodium vivax are the most common types, and Plasmodium falciparum is also the most deadly. Approximately half of the world's population is at risk of malaria. Most malaria cases occur in sub-Saharan Africa; however, Asia, Latin America, and to a lesser extent the Middle East and parts of Europe are also affected. In 2008, malaria was present in 108 countries and territories.

In the human body, the Plasmodium parasites multiply in the liver and then infect red blood cells. Symptoms of malaria include fever, headache, and vomiting and usually appear within 10 to 15 days of the mosquito bite. If not treated within 24 hours, malaria can quickly become life threatening by disrupting blood supply to vital organs. In 2008, [Page 270]there were 247 million cases of malaria and nearly 1 million deaths, mostly among young children in sub-Saharan Africa, where the disease claims the life of a child every 45 seconds. Factors related to the parasite, the vector, the human host, and the environment influence the intensity of malaria transmission. All of the main vector species bite at night, and they breed in shallow collections of freshwater. Transmission is more intense in places where the mosquito has a long life span, which allows the parasite time to reach maturity inside the mosquito. Further, vectors that prefer to bite humans rather than other animals also add to the intensity of transmission. Human immunity, developed over years of exposure, never provides complete protection, though it does reduce the risk that malaria infection will cause severe disease. For this reason, most malaria deaths in Africa occur in young children, although in areas with less transmission and low immunity, all age groups are at risk. Transmission also depends on climate conditions that may affect the abundance and survival of mosquitoes, including rainfall patterns, temperature, and humidity.

Growing resistance to antimalarial medicines has spread rapidly, undermining malaria control efforts. The best available malaria treatment is artemisinin-based combination therapy (ACT); when treated with an artemisinin-based monotherapy, some patients may discontinue treatment early, after the malaria symptoms disappear. This results in partial treatment, with persistent parasites remaining in the patient's blood. Without a second drug given as part of a combination (as is done with an ACT), these resistant parasites persist and can be passed on to a mosquito and then to another person. Monotherapies are therefore the primary force behind the spread of artemisinin resistance. If resistance to artemisinins develops and spreads to other large geographical areas, the public health consequences could be devastating because no alternative antimalarial medicines are expected to be available in the near future.

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