Community structure and insecticide resistance of malaria vectors in northern-central Myanmar

Abstract

Background: Myanmar is one of the six countries in the Greater Mekong Subregion (GMS) of Southeast Asia. Malaria vectors comprise many Anopheles species, which vary in abundance and importance in malaria transmission among different geographical locations in the GMS. Information about the species composition, abundance, and insecticide resistance status of vectorial systems in Myanmar is scarce, hindering our efforts to effectively control malaria vectors in this region.

Methods: During October and November 2019, larvae and adult females of Anopheles mosquitoes were collected in three sentinel villages of Banmauk township in northern Myanmar. Adult female mosquitoes collected by cow-baited tent collection (CBTC) and adults reared from field-collected larvae (RFCL) were used to determine mortality rates and knockdown resistance (kdr) against deltamethrin using the standard WHO susceptibility test. Molecular species identification was performed by multiplex PCR and ITS2 PCR, followed by DNA sequencing. The kdr mutation at position 1014 of the voltage-gated sodium channel gene was genotyped by DNA sequencing for all Anopheles species tested.

Results: A total of 1596 Anopheles mosquitoes from seven morphologically identified species groups were bioassayed. Confirmed resistance to deltamethrin was detected in the populations of An. barbirostris (s.l.), An. hyrcanus (s.l.), and An. vagus, while possible resistance was detected in An. annularis (s.l.), An. minimus, and An. tessellatus. Anopheles kochi was found susceptible to deltamethrin. Compared to adults collected by CBTC, female adults from RFCL had significantly lower mortality rates in the four species complexes. A total of 1638 individuals from 22 Anopheles species were molecularly identified, with the four most common species being An. dissidens (20.5%) of the Barbirostris group, An. peditaeniatus (19.4%) of the Hyrcanus group, An. aconitus (13.4%) of the Funestus group, and An. nivipes (11.5%) of the Annularis group. The kdr mutation L1014F was only detected in the homozygous state in two An. subpictus (s.l.) specimens and in a heterozygous state in one An. culicifacies (s.l.) specimen.

Conclusions: This study provides updated information about malaria vector species composition and insecticide resistance status in northern Myanmar. The confirmed deltamethrin resistance in multiple species groups constitutes a significant threat to malaria vector control. The lack or low frequency of target-site resistance mutations suggests that other mechanisms are involved in resistance. Continual monitoring of the insecticide resistance of malaria vectors is required for effective vector control and insecticide resistance management.

Keywords: Anopheles malaria vectors; Community structure; Insecticide resistance; Kdr mutation; Myanmar; Ribosomal internal transcribed spacer 2.

Fig. 1

Map of study sites in Banmauk Township, Katha District, Sagaing Region of northern-central Myanmar. Red triangles indicate the locations of the three villages. The map was generated using ArcGIS Pro software based on map source at: www.esri.com

Fig. 2

Mortality rate of Anopheles mosquitoes exposed to deltamethrin following the WHO susceptibility test procedure for insecticide monitoring in malaria vectors. The mortality rate was recorded after a 24-h recovery period. NA, not available. Red dashed line indicates cutoff for confirmed resistance (< 90%) (WHO 2018 update). Anopheles sinensis susceptible laboratory strain showed 100% mortality

Fig. 3

Phylogenetic tree inferred from UPGMA method based on ITS2 sequences (a) and kdr sequences (b). Bootstrap support values ≥ 50% are displayed by colored dots next to the branches. Tips of the tree are labeled as GenBank accession followed by Anopheles species identified in this study