Chloroquine efficacy for Plasmodium vivax in Myanmar in populations with high genetic diversity and moderate parasite gene flow

Abstract

Background: Plasmodium vivax malaria remains a major public health burden in Myanmar. Resistance to chloroquine (CQ), the first-line treatment for P. vivax, has been reported in the country and has potential to undermine local control efforts.

Methods: Patients over 6 years of age with uncomplicated P. vivax mono-infection were enrolled into clinical efficacy studies in Myawaddy in 2014 and Kawthoung in 2012. Study participants received a standard dose of CQ (25 mg/kg over 3 days) followed by weekly review until day 28. Pvmdr1 copy number (CN) and microsatellite diversity were assessed on samples from the patients enrolled in the clinical study and additional cross-sectional surveys undertaken in Myawaddy and Shwegyin in 2012.

Results: A total of 85 patients were enrolled in the CQ clinical studies, 25 in Myawaddy and 60 in Kawthoung. One patient in Myawaddy (1.2%) had an early treatment failure and two patients (2.3%) in Kawthoung presented with late treatment failures on day 28. The day 28 efficacy was 92.0% (95% CI 71.6-97.9) in Myawaddy and 98.3% (95% CI 88.7-99.8) in Kawthoung. By day 2, 92.2% (23/25) in Myawaddy and 85.0% (51/60) in Kawthoung were aparasitaemic. Genotyping and pvmdr1 CN assessment was undertaken on 43, 52 and 46 clinical isolates from Myawaddy, Kawthoung and Shwegyin respectively. Pvmdr1 amplification was observed in 3.2% (1/31) of isolates in Myawaddy, 0% (0/49) in Kawthoung and 2.5% (1/40) in Shwegyin. Diversity was high in all sites (H _E 0.855-0.876), with low inter-population differentiation (F _ST 0.016-0.026, P < 0.05).

Conclusions: Treatment failures after chloroquine were observed following chloroquine monotherapy, with pvmdr1 amplification present in both Myawaddy and Shwegyin. The results emphasize the importance of ongoing P. vivax drug resistance surveillance in Myanmar, particularly given the potential connectivity between parasite population at different sites.

Keywords: Chloroquine; Copy number; Diversity; Efficacy; Genotyping; Malaria; Myanmar; Plasmodium; Resistance; Transmission; Vivax; pvmdr1.

Fig. 1

Plasmodium vivax prevalence map illustrating study site locations. This map was generated by the Malaria Atlas Project, University of Oxford. The colour scales reflect the model-based geostatistical point estimates of the annual mean P. vivax parasite rate in the 1–99 year age range (PvPR_1–99) [54] within the stable spatial limits of transmission in 2010. The approximate locations of the study sites described here are indicated with numbers as follows; 1 Insein, Yangon Region; 2 Shwegyin, Bago East Region; 3 Hpa-An, Kayin State; 4 Myawaddy, Kayin State; 5 Kawthoung, Tanintharyi Region

Fig. 2

Flowchart of patients in the clinical study. MYA Myawaddy, KTH Kawthoung

Fig. 3

Barplots illustrating the frequency of multi-allelic loci in the polyclonal infections

Fig. 4

Unrooted neighbour-joining tree illustrating the genetic relatedness between the P. vivax isolates within and among different districts in Myanmar. Only the isolates with complete allelic data across all nine loci are included in the analysis (n = 103)