Malaria parasites develop resistance to drugs

Malaria is showing signs of resistance to the most effective drug, two separate teams of scientists studying the killer disease have warned.

The artemisinin family of drugs, which until now were clearing patients of the protozoan parasite Plasmodium - the group of micro-organisms which causes malaria - within two to three days, is now taking up to five days to effect its cure.

The studies, by American and British scientists, confirm fears raised by the World Health Organisation in 2006 that artemisinins were becoming less effective in Southeast Asia.

The US study found delayed clearance of Plasmodium in between one third and a half of patients. In the UK study, patients living in Cambodia took almost twice as long to clear the malaria parasite as a comparison group in Thailand.

If any species of Plasmodium develops full resistance to artemisinins, the drugs will be only the latest generation in a series of anti-malarials to lose their effectiveness – a trend which in the past has begun in Southeast Asia. The chloroquine and sulfadoxine pyrimethamine groups of drugs have both been compromised over the decades following the evolution of resistant Plasmodium strains in Southeast Asia. SPs were introduced in 1977 with a 100 per cent success rate; within five years it was effective in only 10 per cent of patients.

It is thought that Cambodia's poor public health system and the availability of cheap 'pirate' drugs, which contain small amounts of active anti-malarials in order to pass detector tests, are to blame for the development of resistant Plasmodium strains.

A spokesman for the UK scientists, Professor Nick Day, director of the Mahidol-Oxford Tropical Medicine Research Unit, told the BBC: "Twice in the past, South East Asia has made a gift, unwittingly, of drug resistant parasites to the rest of the world, in particular to Africa.

"If the same thing happens again… there will be devastating consequences for malaria control."

Malaria infects 350-400 million people every year, killing one million. The economic cost to Africa alone is thought to be $12bn annually. While there are other ways of controlling the disease, such as spraying with insecticides to kill mosquitoes, handing out free mosquito nets and releasing sterile male mosquitoes, a new group of anti-malarial drugs to replace artemisinins could be 10 years away from development.

Meanwhile the WHO recommends that in order to slow the spread of resistance, drug companies should only sell artemisinins as part of a cocktail of other anti-malarials.