Study Finds Three Types of Drug Resistant Malaria

An international team of scientists has identified three distinct types of drug resistant malaria in western Cambodia, findings that may assist health workers prevent the further spread of the disease.

Just last week, the World Health Organization launched a three-year emergency response plan covering Cambodia and its neighbors to stop malaria’s growing resistance to the best available drugs—known as Artemisinin Combination Therapies, or ACTs—from reaching Africa, where the parasite claims most of its annual 600,000-plus victims.

Health workers have noticed signs of malaria’s growing resistance to ACTs for years, having first detected it along the Thai-Cambodian border in 2008 and having since spotted it in Vietnam and Burma as well.

The new study, though, published Sunday in the journal Nature Genetics, is the first time researchers have genetically distinguished any ACT resistant strains of the parasite. The team of researchers from 23 institutions spanning Cambodia, Africa, Europe and the U.S. sampled more than 800 genomes of the parasite from seven countries in western Africa and Southeast Asia. Among them they found three unique populations resistant to artemisinin, and all in western Cambodia.

“No study before has really observed artemisinin resistance from a genetic perspective,” said lead author Olivo Miotto, of Oxford University and Mahidol University in Thailand.

“We’re now able to identify these groups by looking at genetic data, so we are now able to monitor these clusters and see where they spread to,” he said.

With these “fingerprints” for each of the three populations now in hand, the results could help health workers spot ACT resistant strains if they show up elsewhere and respond quicker than before.

“Public health authorities need rapid and efficient ways to genetically detect drug-resistant parasites in order to track their emergence and spread,” Mr. Miotto said. “Our approach allows us to identify emerging populations of artemisinin-resistant parasites and monitor their spread and evolution in real time.”

Searching for resistance now means long and involved testing of malaria patients and watching to find out how many of them still carry the parasite after three days on ACTs, the amount of time it typically takes the drugs to do their job. The more patients they find who still carry the parasite after three days, the stronger the signs that malaria is gaining resistance there.

Resistance rates among tested patients in some parts of western Cambodia have now hit 40 percent, well past the 10 percent that health workers mark as cause for concern.

“Artemisinin resistance is an emergency which could derail all the good work of global malaria control in recent years,” said Nicolas White, another author of the paper from Oxford and Mahidol universities, in a statement accompanying the study. “We desperately need methods to track it in order to control it, and molecular fingerprinting provides this.”

But the discovery of three separate strains of artemisinin-resistant malaria could also make their work more complicated, the paper suggests.

The varied strains “with widely different genetic characteristics, suggests that there could be multiple forms of resistance, each of which will need to be controlled,” it reads.

ACTs and other efforts have dramatically brought malaria infection rates and deaths down in recent years.

But another paper released in November predicted that more than 700,000 additional people could die of the parasite over the next five years if artemisinin resistance were to reach Africa.

In Cambodia, staff at the government’s National Malaria Center and the U.S.’ Armed Forces Research Institute of the Medical Sciences helped collect samples for the latest study around the country.

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