Following are some key facts about malaria:
* It is a parasitic infection transmitted by mosquitoes.
* Almost half the world's population -- or 3.3 billion people -- are at risk of malaria and there are around 225 million cases each year. Most at risk are those living in the world's poorest countries.
* Most of the almost 800,000 annual deaths from malaria are among children in Africa under the age of five.
* More than 90 percent of cases are caused by plasmodium falciparum, the most destructive malaria parasite that is found mainly in Africa.
* Symptoms of malaria include fever, headache and vomiting, and usually appear between 10 and 15 days after the mosquito bite. If not treated, malaria can quickly become life-threatening by disrupting the blood supply to vital organs.
* Malaria accounts for around 40 percent of public health spending in sub-Saharan Africa. Malaria-related illnesses and deaths are estimated to cost Africa's economy $12 billion a year and the disease can cut gross domestic product by as much as 1.3 percent in countries with high disease rates, such as Nigeria and the Democratic Republic of Congo.
* Funding to fight malaria has increased substantially in recent years, rising to $1.5 billion in 2010 from around $100 million in 2003, but experts say it would cost an estimated $5 billion a year to fully fund the fight.
* Treating mosquito nets and houses with insecticides is one of the major prevention strategies, but mosquitoes can develop resistance to insecticides, making them ineffective.
* Antimalarial medicines made by drugmakers such as Novartis and Sanofi-Aventis are also very effective. But growing resistance to older antimalarials has spread rapidly, undermining efforts to control the disease.
* An experimental malaria vaccine called RTS,S or Mosquirix is in the final stages of clinical testing in around 16,000 children in Africa. The vaccine, which was shown to be around 50 percent effective in earlier trials, is being developed by British drugmaker GlaxoSmithKline with money from the Gates Foundation-funded PATH Malaria Vaccine Initiative.
SOURCES: Reuters, World Health Organization, Roll Back Malaria and the Malaria Vaccine Initiative
(Compiled by Kate Kelland; Editing by Sophie Hares)