Entomological survey in two communes with residual malaria transmission in Gia Lai Province in the central highlands of Vietnam

Maysa T Motoki,Huan Mah Ro,Manh Duc Nguyen,Michael D Edstein,Thai Quang Nguyen,Weng K Chow,Nicholas J Martin,Jeffrey C Hertz,Vinh Xuan Pham

doi:10.1186/s12936-021-03941-6

Maysa T Motoki, Huan Mah Ro + Show 7 more

Open Access

https://doi.org/10.1186/s12936-021-03941-6

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Abstract

BackgroundIn 2018, the National Malaria Control Programme in Vietnam switched from prioritizing malaria control to elimination. However, with the ongoing elimination programme, there are still areas where residual malaria transmission persists, including the central highlands. This entomological survey was conducted to evaluate Anopheles diversity and host-seeking activity of Anopheles vectors in two communes with very low malaria transmission in Gia Lai Province.MethodsAnopheles species were collected in Ia DReh commune and Ia KDam commune, Gia Lai Province in the central highlands of Vietnam. Collections were conducted using human-baited double net trap, light trap and manual aspiration collections around cattle sheds, in the dry and rainy season. Mosquito specimens were identified morphologically, and members of species complexes were distinguished molecularly. Mosquito night-feeding patterns were investigated during the dry and rainy seasons.ResultsOverall, 18,835 specimens including 19 taxa were collected in Ia KDam and Ia DReh communes. These included the primary malaria vectors, Anopheles dirus and Anopheles minimus, and other secondary vector species. Anopheles dirus was observed to be an anthropophilic species, whereas An. minimus and a number of secondary vectors were observed to be zoophilic. Anopheles vagus was the dominant species, followed by Anopheles sinensis and Anopheles peditaeniatus. The majority of specimens were collected in the rainy season due to the relatively large number of An. vagus, while An. peditaeniatus, An. dirus, Anopheles kochi, Anopheles monstrosus and Anopheles tessellatus were collected in greater numbers during the dry season. The peak of host-seeking activity for An. dirus, An. sinensis, and An. vagus was between 18.00 and 19.00 h.ConclusionThis study provided information on the diversity, seasonal prevalence and behaviour of Anopheles at the study sites. Identifying the diverse mosquito fauna in the central highlands of Vietnam allows species-specific control measures to be implemented by the National Programme to reduce malaria in areas of very low malaria transmission. The peak Anopheles host-seeking activity observed in this study was between 18.00 and 23.00 h, which highlights the need to better characterize Anopheles behaviour in this region of Vietnam to inform on vector control strategies.

Highlights

In 2018, the National Malaria Control Programme in Vietnam switched from prioritizing malaria control to elimination
The strategies of vector control have been the use of long-lasting insecticidal net (LLIN) and insecticide-treated nets (ITNs), where Ia DReh (IDR) has been supplied with LLINs, and Ia KDam (IKD) with LLINs and Insecticide-threated net (ITN) (Gia Lai Province, Center for Disease Control (CDC) pers. comm.)
Anopheles aconitus (77.8%, 7/9) and An. dirus (76.5%, 65/85) were more common in the dry season in IDR, and An. dirus (67%, 2/3) and An. peditaeniatus (80%, 8/10) in IKD; whereas An. sawadwongporni (78.9%, 15/19) was more common in the rainy season in IRD, and An. sawadwongporni (75%, 9/12), An. sinensis (75%, 6/8) and An. vagus (57.4%, 39/68) in IKD (Table 7)

Summary

Introduction

In 2018, the National Malaria Control Programme in Vietnam switched from prioritizing malaria control to elimination. The NMCP recommends the use Nguyen et al Malar J (2021) 20:403 of insecticide-treated nets (ITNs), long-lasting insecticide nets (LLINs), social mobilization, targeted residual indoor spraying, and improved anti-malarial drug treatment These strategies significantly reduced the spread of malaria in many areas in the country [2,3,4]. Despite these measures, there remain residual malaria transmission areas, predominately in forested regions of central and southern Vietnam [5,6,7,8,9,10] These very low malaria transmission areas harbour primary malaria vectors and there are reports that long-lasting insecticidal net (LLIN) use is less common [11, 12]. In deforested rural areas, where land has been cleared for cultivation, many secondary malaria vectors are present and may contribute to maintaining malaria transmission outside of forested areas [10]

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