Biting behavior of malaria vectors and malaria elimination efforts in Tak province, Thailand
A study to investigate behavior of malaria vectors, susceptibility to insecticides and durability of field used Long Lasting Insecticide Treated Nets (LLINs) was conducted on Thai-Myanmar Border at Village No. 12, Ban Huay Pla Kong, Khaneijue Sub-district, Mae Ramat District, Tak Province for 11 months between December 2014 and October 2015. Thirteen species of Anopheles were collected with three malaria vectors and found all year round (i.e. Anopheles minimus, An. maculatus group and An. dirus). An. minimus was found in high density from February to June with highest peak in April. It preferred to bite outdoors than indoors and it was highly zoophilic but there was no statistically significant difference (p=0.079). An. maculatus group showed significant preference to bite humans outdoors than indoors (p=0.030). It was found with high density from April to October with highest peak in June and it was highly zoophilic. Density of An. dirus was insufficient for statistical analysis. These findings indicated that both vector species prefer to bite humans outdoors rather than indoors. Moreover, they were highly zoophilic. This outdoor biting behavior suggested that it may reduce the effective of LLIN and indoor residual spray, which aPre the main vector control measures for malaria elimination. Both An. minimus and An. maculatus group were highly susceptible to deltamethrin, permethrin and bifenthrin. Furthermore, it was found that durability of LLINs manufactured from deltemethrin (55 mg a.i./m2)-coated polyester net could last longer than 5 years and permethrin (2.0% a.i. w/w)-impregnated polyethylene net lasting longer than 4 years, after distribution into this village. These findings provided evidence that durability of LLINs is much longer than the recommendation made by the manufacturers and the World Health Organization (WHO). Findings from the western Thai province of Tak with regard to outdoor biting behavior of malaria vectors and long durability of LLINs may not be conclusive since this was only one study. Further studies in other parts of Thailand should also be conducted to draw more conclusive findings. Data from additional studies will be very useful for policymakers to further review and improve existing vector control measures to advance the country’s malaria elimination program. Findings from this study has also suggested to include adult survey and animal bait collection to determine occurrence of malaria vector for stratification of areas for assignment of malaria elimination and vector control measures.
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