World Malaria Day has been held annually since 2001 Wiki Commons

World Malaria Day recognises the global efforts to control one of the world's most deadly diseases.

It was estabished in 2007 by the World Health Assembly, the decision-making body of the World Health Organisation, from the seeds of Africa Malaria Day. The letter was brought into being in 2001 by the Abuja Declaration, a documentsigned by 44 malaria-endemic countries in an effort to alert the world to the ravages of the mosquito-borne killer.

This year, the theme of World Malaria Day is "Invest in the future: Defeat malaria". It is designed to provide education and understanding and spread information on year-long intensified implementation of national malaria-control strategies, including community-based activities for prevention and treatment in endemic areas.

What is malaria and how is it spread?

Malaria is an infectious disease that affects humans and other animals. It is caused by parasitic protozoans, a type of unicellular microorganism of the genus Plasmodium. Commonly, the disease is transmitted by a bite from an infected female Anopheles mosquito, which introduces the organism from its saliva into a person's circulatory system. In the blood, the parasites travel to the liver to mature and reproduce.

Five species of Plasmodium can infect humans. The vast majority of deaths are caused by P. falciparum and P. vivax, while P. ovale and P. malariae cause a milder form of the disease which is rarely fatal. P. knowlesi is prevalent in southeast Asia and generally causes malaria in macaques, but can also infect humans.

Where is it most common?

The disease is most common in tropical and subtropical regions because mosquitoes thrive in areas with large amounts of rainfall and warm temperatures.

The majority of deaths as a result of malaria occur among African children. Asia, Latin America, areas of the Middle East and parts of Europe are also affected by the tropical disease. Around the world, 3.3 billion people in 106 countries are at risk of malaria.

What the symptoms and how is it tested?

Malaria causes symptoms that typically include fever and headache, in which severe cases can progress to coma or death. The signs of the disease begin eight to 25 days after infection, although symptoms can occur later in those who have taken preventative antimalarial medication. Symptoms can be flu-like, and include joint pain, vomiting, jaundice, convulsions and retinal damage.

The disease is normally diagnosed by the examination of blood using blood films or with antigen-based diagnostic tests. Transmission of malaria can be prevented with the use of mosquito nets and insect repellents. Although no vaccine exists yet, development is in progress. Severe malaria is treated with quinine or artesunate and mefloquine.