Physicians are scrambling to update treatments to combat the growing threat caused by a new strain of malaria that is unique to Cambodia and resistant to the drug that dictates whether patients are ultimately cured.
Since the strain was detected in 2010, the failure rate of anti-malaria combination therapy has risen to 40 per cent in the Kingdom due to the strain’s resistance to the drug piperaquine, which is used in tandem with artemisinin, Pasteur Institute senior researcher Dr Benoit Witkowski said yesterday.
The Cambodia National Malaria Center (CNM) was unable to confirm the figures, but health research unit head Dr Leng Rithea confirmed that they have recorded clinical failures from the combination therapy.
Cambodians’ resistance to artemisinin, the drug that acts as a booster to piperaquine and provides the most rapid action against malaria, has been widely publicised since a resistant strain was first discovered on the Thai-Cambodian border 10 years ago. Within a decade, it had led to almost 100 per cent resistance in some parts of the country, especially in western Cambodia, Witkowski added.
Research and studies on piperaquine resistance, however, are only starting to develop, but early data identify Cambodia – specifically its western region – as ground zero for a unique epidemic.
“Cambodia has always been a place where parasites become more easily resistant than other parts of the world,” said Dr Pascal Ringwald, drug resistance unit coordinator at the WHO’s Geneva headquarters. “But resistance to piperaquine is far more worrying than resistance to artemisinin.”
“It’s not yet a huge threat for patients today, but if piperaquine loses its effectiveness, then it will be a really big problem,” Ringwald said.
Artemisinin decreases the number of parasites in a patient’s blood, but its relative ineffectiveness leaves the task of fighting the lion’s share of parasites to piperaquine. This phenomenon overwhelms the drug and later renders it incapable of complete parasite eradication.
“So far, we have detected the reappearance of the same parasites two or three weeks after treatment because of this resistance,” Witkowski said.
According to the WHO’s 2014 World Malaria Report, though malaria continues to pose a risk to 44 per cent of Cambodia’s population, mortality rates plummeted to 21,309 in 2013 from nearly 50,000 in 2010. The improvement, Ringwald said, is largely attributable to Cambodia’s “excellent health care network and dedication to fighting the disease”.
But Cambodia’s strong record of eradicating the disease might be under threat if piperaquine resistance continues to spread within the population.
If piperaquine loses its edge, said Dr Charles Woodrow, senior clinical research fellow of the Mahidol-Oxford Research Unit in Bangkok, Cambodia might have to resort to using two other combination therapies available in Southeast Asia.
“This is just a short-term fix, though, as changing therapies might lead to a different partner drug resistance … and once the population develops resistance to other therapies, we are left empty-handed,” Woodrow said.
To stay one step ahead of the issue, Ringwald said that the CNM and its partners are studying new drugs or considering the use of two partner drugs along with artemisinin.
“Though there’s some treatment failure, it’s not a failure everywhere, so we can still use the current therapy,” Rithea said. “But we are conducting efficacy studies and also working on the new treatment guidelines for Cambodia.”
The Pasteur Institute is also currently performing its own study to further understand the scope and the as-yet-unclear contributing factors of the growing resistance.
“We are all trying to figure this out and whether there are other incidences of it around the world that have yet to be detected.”
But Woodrow said the situation comes as “no surprise”.
“It all fits together, because if you want to see partner drug resistance, you go to the place that has the longest artemisinin resistance because the two are interdependent,” he said. “So the question is now what are the scientific and public health communities going to do about it?”