Poster Presentation First Malaria World Congress 2018

Monitoring susceptibility of Plasmodium falciparum isolates to artemisinin combinations in Ninh Thuan Province, south-central Vietnam (#429)

Nguyen V Thanh 1 , Nguyen C Phong 1 , Huynh H Quang 1 2 , Nguyen N San 1 , Kerryn Rowcliffe 3 , Ilin Chuang 4 , Nicholas J Martin 5 , Nguyen D Manh 1 , Michael D Edstein 3 , Marina Chavchich 3
  1. Vietnam People's Army Military Institute of Preventive Medicine, Hanoi, Vietnam
  2. Institute of Malariology, Parasitology and Entomology, Quy Nhon, Vietnam
  3. Australian Defence Force Malaria and Infectious Disease Institute, ENOGGERA, QLD, Australia
  4. US Naval Medical Research Center, Silver Spring, USA
  5. US Naval Medical Research Center-Asia, Singapore

In Vietnam, the artemisinin-based combination therapy (ACT) of dihydroartemisinin-piperaquine (DHA-PPQ) is used for first-line treatment of Plasmodium falciparum malaria. DHA-PPQ resistance is present in Binh Phuoc province in south Vietnam with failure rates of 26% in 2015. Therapeutic efficacy studies (TES) of DHA-PPQ have revealed a delayed parasite clearance in Dak Nong, Gia Lai, Khanh Hoa, Quang Nam and Ninh Thuan provinces with over 10% of patients microscopically positive on day 3 after starting treatment prompting concerns of declining efficacy of DHA-PPQ and emphasizing the importance of monitoring resistance.

In 2015-2016, in Ninh Thuan province we conducted a TES of ACTs (artesunate for 4 days followed by DHA-PPQ for 3 days versus a 3-day course of artemether-lumefantrine), which revealed the ACTs to be curative in treating P. falciparum infections. As part of the TES the in vitro susceptibility of 11 P. falciparum isolates to 9 antimalarials was characterized using the hypoxanthine incorporation assay. Of these, a sub-set of 5 P. falciparum isolates were assessed using the ring stage survival assay (RSA) and the piperaquine survival assay (PSA), recognized methods for predicting delayed parasite clearance and treatment failures with DHA-PPQ. The P. falciparum MRA1239 (DHA-sensitive) and MRA1240 (DHA-resistant) isolates, both from Cambodia, were used as references in the RSA and PSA. The in vitro findings showed that in the RSA the survival rates ranged between 0.7-1.5% (<10.88% cut-off) for the field isolates, greater than that for MRA1239 (0.16%), but markedly lower than that for MRA1240 (7.3%). In the PSA the field isolates and both MRA lines were sensitive to PPQ, with survival rates ranging 1.8 to 4.8% (<10% cut-off). These data provide additional evidence and confirmation of the clinical findings on efficacy of DHA-PPQ at the field site, but also reinforces the need for monitoring emerging resistance.