Characterization of Plasmodium falciparum and Plasmodium vivax recent exposure in an area of significantly decreased transmission intensity in Central Vietnam

Abstract

BackgroundIn Vietnam, malaria transmission has been reduced to very low levels over the past 20 years, and as a consequence, the country aims to eliminate malaria by 2030. This study aimed to characterize the dynamics and extent of the parasite reservoir in Central Vietnam, in order to further target elimination strategies and surveillance.MethodsA 1-year prospective cohort study (n = 429) was performed in three rural communities in Quang Nam province. Six malaria screenings were conducted between November 2014 and November 2015, including systematic clinical examination and blood sampling for malaria parasite identification, as well as molecular and serological analysis of the study population. Malaria infections were detected by light microscopy (LM) and quantitative real time PCR (qPCR), while exposure to Plasmodium falciparum and Plasmodium vivax was measured in the first and last survey by ELISA for PfAMA1, PfGLURP R2, PvAMA1, and PvMSP1-19. Classification and regression trees were used to define seropositivity and recent exposure.ResultsFour malaria infections (2 P. falciparum, 2 P. vivax) were detected in the same village by qPCR and/or LM. No fever cases were attributable to malaria. At the same time, the commune health centre (serving a larger area) reported few cases of confirmed malaria cases. Nevertheless, serological data proved that 13.5% of the surveyed population was exposed to P. falciparum and/or P. vivax parasites during the study period, of which 32.6% were seronegative at the start of the study, indicating ongoing transmission in the area. Risk factor analysis for seroprevalence and exposure to P. falciparum and/or P. vivax identified structural or economic risk factors and activity/behaviour-related factors, as well as spatial heterogeneity at the village level.ConclusionsPrevious studies in Central Vietnam demonstrated high occurrence of asymptomatic and sub-microscopic infections. However, in this study very few asymptomatic infections were detected despite serological evidence of continued transmission. Nonetheless, the factors associated with spatial heterogeneity in transmission could be evaluated using serological classification of recent exposure, which supports the usefulness of serological methods to monitor malaria transmission.Electronic supplementary materialThe online version of this article (10.1186/s12936-018-2326-1) contains supplementary material, which is available to authorized users.

Molecular surveillance and temporal monitoring of malaria parasites in focal Vietnamese provinces

“…In addition, it was reported that between 2006 and 2010, 70% of infections in Vietnam were due to P. falciparum . However, due to control measures, there has been a stronger impact on P. falciparum than on P. vivax since 2014, resulting in an almost equal ratio of both species [ 27 ]. Furthermore, co-infections with P. knowlesi and P. vivax have been documented in mosquitoes and humans in South Vietnam [ 28 ].…”

Cross-sectional study of asymptomatic malaria and seroepidemiological surveillance of seven districts in Gia Lai province, Vietnam

“…Such serological tools are of special interest in pre-elimination scenarios existing in Vietnam, with marked spatial transmission heterogeneity ( i.e. hotspots of transmission surrounded by areas of no transmission), where geographical stratification in transmission levels becomes essential to target NMCP interventions efficiently [ 18 ].…”

High proportion of genome-wide homology and increased basal pvcrt levels in Plasmodium vivax late recurrences: a chloroquine therapeutic efficacy study

“…<Day 28) (20,21,23), only one confirmed recurrent infections (n=3) with blood CQ concentration above MEC in Quang Nam in 2011 (20). Although the present study was conceived as a continuation of CQR monitoring in Quang Nam province (20), malaria cases rapidly decreased there after 2013, with mostly residual P. vivax by 2015, which was insufficient to conduct classical TES designs due to obvious time and logistic constraints (48). The primary endpoints presented in this study suggest CQ remained largely efficacious in Gia Lai province until 2017, with mostly late recurrences detected after Day 28 in the presence of blood CQ concentrations below MEC, similar to findings in the southern province of Binh Phuoc (22).…”