Artemisinin resistance emerged on Thai-Myanmar border 'years ago'

A new study has shown that resistance to artemisinin — a front-line malaria treatment — developed in parasites along the border between Thailand and Myanmar at least eight years ago, and is threatening initiatives to reduce the global burden of the disease.

Resistance to other key malaria drugs is known to have spread from Cambodia into Asia and Sub-Saharan Africa, leading to millions of deaths. As a result, researchers need to establish whether artemisinin-resistant parasites that have been identified in Cambodia could be spreading in the same way.

The researchers analysed the rates at which malaria parasites were cleared from the bodies of patients receiving oral artemisinin drugs at clinics along the northwest Thai border between 2001 and 2010.

Writing in The Lancet last week (5 April), they reported a steady fall in parasite clearance rates over the course of the study, a clear indication of growing drug resistance that began at least eight years ago, and which is on track to equal those in Cambodia within six years.

However they said they had not been able to determine whether disease resistant parasites had emerged independently on the Thai–Myanmar border, or had arrived from Cambodia.

Either way, they said there were immediate implications for current containment and control strategies.

"The bottom line is that artemisinin resistance is not restricted to a small focus point in Cambodia and is actually more widespread — so attempts to control [the disease] really need to be re-thought," Tim Anderson, contributing author and geneticist at the Texas Biomedical Research Institute, United States, told SciDev.Net.

This is particularly the case in Myanmar, where public health infrastructure is weak, according to a commentary accompanying the Lancet paper written by Anne-Catrin Uhlemann and David Fidock from Columbia University's College of Physicians and Surgeons in the United States.

"If resistance to artesminin spreads beyond the limited area where it was been identified, this will be a major disaster," Martin de Smet, head of the Belgium-based Médecins Sans Frontières's Working Group on Malaria, told SciDev.Net.

He called for strengthened intervention efforts in Asia, and a greater focus on preventing the emergence of artemisninin-resistance in Africa.

In a separate study published in Science on the same day, a major region of the malaria parasite genome associated with artemisinin resistance has been identified.

Researchers analysed the genome of 91 Plasmodium falciparum parasites from Cambodia, Laos and Thailand. They found evidence of recent strong evolutionary selection in 33 regions of the parasite's genome.

They assessed these regions in relation to parasite clearance rates in Thai patients receiving drug treatment from 2001–2010. Two adjacent areas on chromosome 13 showed a strong relationship with reduced clearance rates.

The next step is to identify the specific mutations responsible for resistance, according to Ian Cheeseman, lead author of the study.

"[This] will allow us to determine how resistance is spreading through South East Asia and potentially, globally — and to contain it," he told SciDev.Net.

He said it might also provide a better understanding of how the drug works. "If we can understand that, then we will be in a position to potentially modify the drug to restore efficacy," he said.

Link to The Lancet abstract

Link to article in Science