Key facts

• Malaria is a life-threatening disease caused by parasites that are transmitted to people through the bites of infected mosquitoes.
• A child dies of malaria every 30 seconds.
• There were 243 million cases of malaria in 2008, causing nearly 863,000 deaths, mostly among African children.
• In Americas, 560,854 cases of malaria and 89 deaths were reported in 2008.
• Malaria is preventable and curable.
• Approximately half of the world's population is at risk of malaria, particularly those living in lower-income countries.
• Travellers from malaria-free areas to disease "hot spots" are especially vulnerable to the disease.
• Malaria takes an economic toll - cutting economic growth rates by as much as 1.3% in countries with high disease rates.

Malaria is caused by parasites of the species Plasmodium. The parasites are spread to people through the bites of infected mosquitoes.

There are four types of human malaria:

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

Plasmodium falciparum and Plasmodium vivax are the most common. Plasmodium falciparum is the most deadly. In Americas 77% of the infections are due to Plasmodium vivax.

Transmission

Malaria transmission rates can differ depending on local factors such as rainfall patterns (mosquitoes breed in wet conditions), the proximity of mosquito breeding sites to people, and types of mosquito species in the area. Some regions have a fairly constant number of cases throughout the year - these countries are termed "malaria endemic". In other areas there are "malaria seasons" usually coinciding with the rainy season.

Large and devastating epidemics can occur when the mosquito-borne parasite is introduced into areas where people have had little prior contact with the infecting parasite and have little or no immunity to malaria, or when people with low immunity move into areas where malaria cases are constant. These epidemics can be triggered by wet weather conditions and further aggravated by floods or mass population movements driven by conflict.

Do all mosquitoes transmit malaria?

Symptoms

The common first symptoms – fever, headache, chills and vomiting – usually appear 10 to 15 days after a person is infected. If not treated promptly with effective medicines, malaria can cause severe illness and is often fatal.

Who is at risk?

Most cases and deaths are in sub-Saharan Africa. However, Asia, Latin America, the Middle East and parts of Europe are also affected. In 2006, malaria was present in 109 countries and territories.

Specific risks follow.

• Travellers from malaria-free regions, with little or no immunity, who go to areas with high disease rates are very vulnerable.
• Non-immune pregnant women are at high risk of malaria. The illness can result in high rates of miscarriage and cause over 10% of maternal deaths (soaring to a 50% death rate in cases of severe disease) annually.
• Semi-immune pregnant women risk severe anaemia and impaired fetal growth even if they show no signs of acute disease. An estimated 200 000 of their infants die annually as a result of malaria infection during pregnancy.
• HIV-infected pregnant women are also at increased risk.