BackgroundSingle amino acid substitutions in the voltage-gated sodium channel associated with pyrethroid resistance constitute one of the main causative factors of knockdown resistance in insects. The kdr gene has been observed in several mosquito species; however, point mutations in the para gene of Aedes aegypti populations in Myanmar have not been fully characterized. The aim of the present study was to determine the types and frequencies of mutations in the para gene of Aedes aegypti collected from used tires in Yangon City, Myanmar.Methodology/Principal FindingsWe determined high pyrethroid resistance in Aedes aegypti larvae at all collection sites in Yangon City, by using a simplified knockdown bioassay. We showed that V1016G and S989P mutations were widely distributed, with high frequencies (84.4% and 78.8%, respectively). By contrast, we were unable to detect I1011M (or I1011V) or L1014F mutations. F1534C mutations were also widely distributed, but with a lower frequency than the V1016G mutation (21.2%). High percentage of co-occurrence of the homozygous V1016G/S989P mutations was detected (65.7%). Additionally, co-occurrence of homozygous V1016G/F1534C mutations (2.9%) and homozygous V1016G/F1534C/S989P mutations (0.98%) were detected in the present study.Conclusions/SignificancePyrethroid insecticides were first used for malaria control in 1992, and have since been constantly used in Myanmar. This intensive use may explain the strong selection pressure toward Aedes aegypti, because this mosquito is generally a domestic and endophagic species with a preference for indoor breeding. Extensive use of DDT for malaria control before the use of this chemical was banned may also explain the development of pyrethroid resistance in Aedes aegypti.

BackgroundMosquito-borne diseases are prevalent in Myanmar, with the number of dengue cases showing a significant increase in recent years. Dengue vectors have developed resistance to insecticides and currently used larvicides show only short-term effectiveness. As a result, an alternative larvicide is urgently needed. The present study evaluated the larvicidal effectiveness of long-lasting pyriproxyfen resin discs (SumiLarv®2MR) against dengue virus vectors in schools in Hlaing Thar Yar Township, Yangon.ResultsThe proportion of Aedes mosquito-infested containers was significantly reduced in the schools applied with the larvicide (OR: 0.24, 95% CI: 0.12–0.48) while there was little reduction noted in the control schools (OR: 0.97, 95% CI: 0.55–1.72). The density of infested containers was also significantly reduced in the intervention schools (Beta: -1.50, 95% CI: -1.98– -1.04), but there was no significant reduction in density in the control schools (Beta: -0.19, 95% CI: -0.53–0.14). The proportion of adult emergence was less than 20% in the treated water collected from the intervention schools for six months, while the proportion was over 90% in the untreated water. In addition, eight-month-old SumiLarv®2MR resin discs were still 100% effective when tested in the laboratory. More than 50% of the discs disappeared from treated containers within two months of intervention.ConclusionsSumiLarv®2MR was effective in reducing Aedes-infested containers at least six months after its application in schools. This new pyriproxyfen formulation has great potential for improving the current dengue vector control program in Myanmar.

Vector bionomic and evaluation of insecticide efficacy were carried out in Koe Mine, Man Aung and 14 Mine areas of Ye Township, Mon State from July 2018 to August 2019 for better understanding of the Anopheles species distribution current insecticide susceptibility status and potential vector of malaria. Mosquitoes were collected using cattle baited net and light traps and larval survey was conducted in water well using WHO dipper. Standard WHO insecticide susceptibility was employed using field collected specimens. Results revealed that all total of 684 and 89 Anopheles mosquitoes consisted of 9 and 5 specie were collected from Koe Mine and Man Aung villages. Main vector An. minimus (6.58% & 3.37%) and Secondary vector An. maculatus (52.34%&37.08%) was collected in high density, An. philippinensis and An. jamesii adult was observed low density in both areas. Other species of An. willmori, An. annularis, An. kochi and An. aconitus were collected in Koe Mine village. All collected Anopheles mosquitoes were found sporozoite negative. These mosquitoes were also collected in indoor, outdoor and cow shed morning resting collected in low density. Susceptibility status of all collected Anopheles were found susceptible to WHO recommended insecticides. Although main vector of An. minius and secondary vectors of Anopheles were available in the villages moreover there is also filarial vector Culex quinquefasciatus mosquitoes larvae were observed high density and co breeder with An. minimus larvae and also DHF vector Aedes aegypti, Ae. albopictus and a new species of Ae. cogilli were also breeding in some water wells. There is high risk for the transmission of malaria, filarial and DF/DHF in both study areas, if diseases carrier is available in the villages and need to proper control measure as use of insecticide treated bed nets and application of focal residual spray for adults as well as treatment of abate or larvivorus fishes in water wells for larvae control to prevent vector borne diseases transmission in these areas.