Two and a half years after insecticide treated bed nets cut the number of cases of the disease, they have risen even higher than before, especially in adults and older children. A study in a village in Senegal, west Africa suggests that mosquitoes develop resistance to the insect-killing chemical that coats the nets. Also, people may lose their immunity to the malaria parasite when the mosquito population falls, and then be exposed when the pest recovers, it suggests.
From August 2008 to August 2010, malaria fell dramatically, to less than eight per cent of the pre bed net level, researchers found. But between September and December 2010, the numbers rose sharply again, to 84 per cent of previous levels. In adults and children aged 10 or more, the rate was even higher than before.
The finding by doctors at the Institute for Development Research in Dakar, triggers alarm about the worldwide strategy, led by Bill Gates, to wipe out malaria by handing out insecticide-treated bed nets and drugs to the 2.5 billion people who live in high-risk areas.
"These findings are of great concern," said Jean-Francois Trape who led the research. "They support the idea that insecticide resistance might not permit a substantial decrease in malaria morbidity in many parts of Africa," said his team’s report in British journal, The Lancet Infectious Diseases.
The finding raises doubts about the worldwide strategy, led by Bill Gates, the world's biggest philanthropist threw down a challenge to the global health community in 2007 to wipe out the disease in his lifetime. It made funding for malaria control soar to more than $10 billion (£6.5 billion), a hundredfold rise in a decade.
Since 2000, more than 300 million bed nets have been given out and are estimated to have saved more than one million lives, according to the Roll Back Malaria Partnership.But the new study raises the question whether the strategy may do more harm than good by encouraging a resurgence of the disease that is worse than before.
Malaria is a tropical disease spread by night-biting mosquitoes. When a mosquito infected with malaria parasites bites, it injects the parasites into the body. It only takes a single mosquito bite for someone to become infected. Malaria is a huge worldwide problem. The World Health Organisation (WHO) estimates that there were 243 million cases and nearly 1 million deaths from malaria in 2008. Most deaths occur in African countries close to the equator and below the Sahara desert. Babies and children are especially vulnerable. A child dies of malaria every 30 seconds, according to WHO estimates.