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 and Plasmodium vivax are the most common. Plasmodium falciparum is the most deadly. In Americas 77% of the infections are due to Plasmodium vivax.
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.
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.
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.
Regional Office for the Americas of the World Health Organization