The disease that continues to kill 2.7 million people every year.
In December 2008, researchers at the annual meeting of the American Society of Tropical Medicine and Hygiene warned that malaria is no longer just a developing-country problem. Global warning and international travel are increasing the risk that the disease could spread to previously malaria-free zones of the United States of America and Europe. An infected mosquito can get onto a plane in an affected region, get off again in a new country and bite someone in or near the airport. Or an infected traveller may travel home and be bitten by a local mosquito, which then becomes infected and bites someone else in the area. In a warming world, where mosquitoes live longer and lay more eggs, the infection can then take hold in mosquito and human populations of the destination country.
The news is cause for concern in the West because there is as yet no vaccine against malaria - and the parasite develops resistance to anti-malarial drugs very quickly. A study published in July 2009 shows that malaria parasites in western Cambodia have now become resistant to artemisinin-based therapies, the current first-line treatment and most effective drug in the world's arsenal against the disease.
This is disturbing news, because although malaria is a curable disease, it has to be treated promptly and adequately - the parasite must be completely eliminated from the body so that it cannot linger to develop resistance to the drug being used. Untreated or inadequately treated malaria kills 2.7 million people each year. Most are children, but other vulnerable groups include pregnant women, travellers who have not had a chance to build up immunity to the disease, refugees, or labour forces entering endemic areas.
There is also a wider social and economic impact on entire communities. The local labour force may be decimated by death and fever, children orphaned and left dependent on communal resources, or parents left childless and without the support they need to hunt, farm and or carry out other survival activities.
The culprit in the transmission of the disease is the female Anopheles mosquito. Through its role in transmitting malaria and yellow fever, it is claimed that this tiny creature has killed more than half the humans that have ever lived. It has also been around a lot longer than modern humans fossils of mosquitoes up to 30 million years old show that the malaria vector was around then, whilst we can only trace our earliest ancestors back to around six million years ago.
The disease itself is caused by the Plasmodium parasite - a tiny single-celled parasite carried by the Anopheles mosquito that infects the cells in our bodies. Four species of the Plasmodium parasite cause human malaria of differing degrees of severity: P. falciparum, P. vivax, P. ovale and P. malariae.
The recently completed Malaria Atlas Project - the most detailed map ever created of malaria risk worldwide - shows that 2.4 billion people are at risk from P. falciparum, the most deadly form of malaria, but highlights some promising news: three-quarters live in areas where risk is considered very low and the technical obstacles to malaria control are relatively small.
Scientific developments are also bringing hope to the fight against the disease. In 2002, the genomes of the P. falciparum parasite and Anopheles gambiae mosquito were published. These are now helping researchers to tease apart the interactions between the parasite and humans, and the parasite and mosquitoes, as it moves through the different stages of its lifecycle.