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

Abstract

Background Malaria elimination by 2030 is an aim of many countries in the Greater Mekong Sub-region, including Vietnam. However, to achieve this goal and accelerate towards malaria elimination, countries need to determine the extent and prevalence of asymptomatic malaria as a potential reservoir for malaria transmission and the intensity of malaria transmission. The purpose of this study was to determine the prevalence of asymptomatic malaria and seropositivity rate in several districts of Gia Lai province in the Central Highlands of Vietnam. Methods A cross-sectional survey of asymptomatic malaria and serological testing was conducted in 3283 people living at 14 communes across seven districts in Gia Lai province in December 2016 to January 2017. Finger prick capillary blood samples were tested for malaria using rapid diagnostic testing and polymerase chain reaction (PCR), as well as detecting antibodies against 3 Plasmodium falciparum and 4 Plasmodium vivax antigens by indirect enzyme-linked immunosorbent assay (ELISA). Age-seroprevalence curves were fitted using reverse catalytic models with maximum likelihood. Results The study population was predominantly male (65.9%, 2165/3283), adults (88.7%, 2911/3283) and of a minority ethnicity (72.2%, 2371/3283), with most participants being farmers and outdoor government workers (90.2%, 2960/3283). Using a small volume of blood (≈ 10 µL) the PCR assay revealed that 1.74% (57/3283) of the participants had asymptomatic malaria (P. falciparum 1.07%, P. vivax 0.40%, Plasmodium malariae 0.15% and mixed infections 0.12%). In contrast, the annual malaria prevalence rates for clinical malaria in the communities where the participants lived were 0.12% (108/90,395) in 2016 and 0.22% (201/93,184) in 2017. Seropositivity for at least one P. falciparum or one P. vivax antigen was 38.5% (1257/3262) and 31.1% (1022/3282), respectively. Age-dependent trends in the proportion of seropositive individuals in five of the districts discriminated the three districts with sustained low malaria prevalence from the two districts with higher transmission. Conclusions Asymptomatic Plasmodium carriers were found to be substantially more prevalent than clinical cases in seven districts of Gia Lai province, and a third of the population had serological evidence of previous malaria exposure. The findings add knowledge on the extent of asymptomatic malaria and transmission for developing malaria elimination strategies for Vietnam.

Seroepidemiological surveillance, community perceptions and associated risk factors of malaria exposure among forest-goers in Northeastern Thailand

“…Overall results show that humoral antibodies against P. falciparum antigens were higher than P. vivax antigens. This finding is consistent with previous studies in low transmission settings in Tak Province in Northwestern Thailand ( Baum et al., 2016 ) and other areas in Southeast Asia, namely, Indonesia ( Surendra et al., 2019 ), Myanmar ( Edwards et al., 2021 ), and Vietnam ( San et al., 2022 ). The dominance in exposure to P. falciparum could be attributed to the timing of data collection, which mainly occurred after the transmission season.…”

“…The relationship between age and seroprevalence rates was similar in all studied areas, increasing with age, peaking at 46–60 years, then decreasing with age. In addition, seroprevalence and SCRs were higher in the older age group, indicating that the age-specific antibody response reflects cumulative exposure or population behavioral differences ( San et al., 2022 ).…”

Naturally acquired antibody response to Plasmodium falciparum and Plasmodium vivax among indigenous Orang Asli communities in Peninsular Malaysia

“…The serological investigation in the present study revealed that humoral antibodies against P. falciparum antigens were higher than P. vivax antigens (i.e., 58% and 10%, respectively). This finding is consistent with previously described levels in other countries in the Southeast Asia region with P. falciparum-P. vivax co-endemic, such as Thailand (79% and 40%) (Rahim et al, 2022), Vietnam (38% and 31%) (San et al, 2022), Myanmar (30% and 14%) (Edwards et al, 2021), and Indonesia (6.9% and 2.0%) (Surendra et al, 2019). The higher seropositivity from P. falciparum may be due to the fact that serological assay used was originally developed to detect responses to PfAMA-1 and PfMSP-1 19 antigens and thus may be more sensitive in detecting this species (Tadesse et al, 2017;Björkman et al, 2019;Edwards et al, 2021).…”

Surveillance of pfhrp2 and pfhrp3 gene deletions among symptomatic Plasmodium falciparum malaria patients in Central Vietnam

“…The levels of HRP2 protein were measured in all RDT negative/LM positive samples and a random selection of RDT positive samples. Protein elution was conducted from 2 × 5 mm punch of DBS (equivalent to 11.2 μl of blood or 5.6 μl of plasma, [ 18 ]), with a final elution in 1120 μl of buffer (1/200) [ 19 ]. Quantitative ELISA-based detection was conducted using Quantimal™ CELISA Ultra-sensitive PfHRP2 Malaria (Cellabs, Australia) according to manufacturer’s instructions [ 20 ].…”