Gene sequencing helps identify drug-resistant malaria

Know your enemy and the fight becomes easier. Researchers have pinpointed three sub-populations of the malaria parasite Plasmodium falciparum that appear to be a major force in drug resistance. The findings could help efforts to track the spread of resistant malaria in future.

The first signs of resistance to the front-line malarial drug artemisinin emerged in Cambodia in 2009. If this resistance spreads worldwide, it will leave people with malaria without an effective drug to treat their illness.

Olivo Miotto at the University of Oxford, and a large international team, studied the genomes of 825 malarial parasites from south-east Asia and west Africa in an effort to understand why some parasite populations become resistant.

The work identified three drug-resistant P.?falciparum sub-populations in western Cambodia that were different from each other, and different from populations in eastern Cambodia, neighbouring countries and west Africa.

"For the first time we have identified the emergence of sub-populations associated with a drug resistance to artemisinin," says Miotto.

Why Cambodia?

Cambodia is thought to be a breeding ground for resistance. Past drug therapies in the country encouraged sole use of artemisinin to treat malaria, which could have been a factor.

Demographic factors could also have played a part: the Khmer Rouge regime of the late 1970s left the country with poor infrastructure and small, isolated communities. In those circumstances, a resistant strain can replicate itself quickly through inbreeding: in west Africa there is more outbreeding, which may slow the spread of resistance there.

"This research sheds light on the evolution of artemisinin resistance and suggests that the situation is more complicated than we thought," says Lisa Ranford-Cartwright from the University of Glasgow, UK, who was not involved in the study.

A full understanding of the mechanisms that build resistance is still out of reach, but the new study does mean researchers will be able to use genetic tests to identify any geographical spread of the three resistant sub-populations in future.

"Being able to detect if there is a sudden explosion of one particular type of parasite will indicate if something is going wrong," Miotto says.

Journal reference: Nature Genetics, DOI: 10.1038/ng.2624

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