Malaria has plagued man since ancient times and nowadays it is estimated to threaten 40% of the world's population, mostly in poor tropical and sub-tropical countries. No-one knows for sure how many people contract the disease and estimates vary. The latest official study puts the figure at between 350 million and 500 million a year. Malaria is preventable and curable, but can be fatal if not treated promptly. It kills more than a million people a year - mostly young children in sub-Saharan Africa - and is a factor in many other deaths.
Malaria got its name - literally meaning bad air - because of a once prevalent belief that foul vapours from swamps or marshes were to blame. Proof that microscopic mosquito-borne parasites were the cause came just over 100 years ago. Although malaria has been eradicated from temperate regions, travellers can catch and bring back "imported malaria". And, more rarely, cases of "airport malaria" occur, blamed on mosquitoes aboard aircraft returning from infected areas.