Antimalarial efficacy of artemisinin-based combination therapies, the first-line treatment against Plasmodium falciparum malaria, relies on both fast-acting artemisinin derivatives and long-lasting partner drugs. The Mekong sub-region of Southeast Asia is currently the epicentre of Plasmodium falciparum multidrug resistance and is facing high rates of dihydroartemisinin-piperaquine treatment failures, one of the most commonly used treatments against malaria.

Antimalarial drug resistance threatens the recent gains made against malaria infection across the Mekong subregion. Genetic tools to detect multidrug-resistant malaria parasites are now being widely used in the region, especially to track the presence of the K13 mutation associated with artemisinin resistance and also the newly identified plasmepsin-2 genetic marker associated with resistance to partner drug, piperaquine.

The Institut Pasteur in Cambodia, with support from WWARN, has developed a procedure to help identify P. falciparum susceptibility to piperaquine more effectively in the laboratory. The Piperaquine survival assay (PSA) measures P. falciparum susceptibility to piperaquine with a better effectiveness than conventional assays. The principle of the assay is straightforward. Parasites are exposed to a unique and pharmacologically relevant dose of piperaquine and then the survival of the parasite is measured. This assay can be performed either from adapted parasites or fresh samples with a high relevance in both cases.

“This assay is an extremely useful way to track and assess resistance to the artemisinin partner drug piperaquine in the field. It will be especially useful in areas where artemisinin resistance is established, such as Southeast Asia, where dihydroartemisinin-piperaquine (DP) is commonly used as a treatment against malaria infection,” says Dr Benoit Witkowski, researcher at Institut Pasteur, Cambodia and Scientific Coordinator of the WWARN In Vitro Group.

To tie in with the launch of this new assay, the team at Institut Pasteur in Cambodia, in collaboration with the WWARN Asia Regional Centre, held a one-week workshop dedicated to PSA training in Cambodia in January. The objectives of the training were to:

“This workshop gave me first-hand knowledge on how to correctly perform this assay directly from the Institut Pasteur in Cambodia in vitro team who developed the method.” says Nguyen Thanh Tong, laboratory technician at the Oxford University Clinical Trials Unit, Vietnam who attended the workshop. “The training has made me more confident in undertaking the assay in my lab and providing training for others.”

To build on the recent progress to improve surveillance of multi-drug resistance to artemisinin combination therapies, the WWARN team have also updated the ACT partner drug Molecular Surveyor  to include data from the plasmepsin-2 resistance marker. The Surveyor now includes recent unpublished plasmepsin-2 marker data from 309 samples. This update will allow researchers and policy makers to track and monitor the spread and emergence of resistance to ACT partner drugs and as well as informing surveillance strategies.

“We have to eliminate falciparum malaria from the region now before it becomes close to untreatable because of drug resistance,” says Dr Didier Menard, Institut Pasteur in Cambodia and Head of the WWARN In Vitro Scientific Group. “Previously, our focus has been on maintaining the efficacy of artemisinin derivatives. It’s now important that we turn our attention to also maintaining the efficacy of the equally important partner drugs. These initiatives from the Institut Pasteur in Cambodia are striving to do this.”