Historical survey of the kdr mutations in the populations of Anopheles sinensis in China in 1996-2014.

Yan Wang,Jiannong Xu,Yajun Ma,Hua Shi,Wanqin Yu,Zhenzhou Yang

doi:10.1186/s12936-015-0644-0

Abstract

BackgroundAnopheles sinensis has become an important malaria vector in China. The long-term extensive utilization of pyrethroids for ITNs and IRS for mosquito control in the last three decades has resulted in the occurrence of resistant An. sinensis populations in many regions. Knockdown resistance (kdr), caused by point mutations in the VGSC gene, is one of the mechanisms that confer resistance to DDT and pyrethroids. Recently, several investigations revealed the kdr occurrence in some An. sinensis populations, however, no kdr data were available earlier than 2009. A survey tracking the dynamics of the kdr mutations in past decades would provide invaluable information to understand how the kdr alleles spread in mosquito populations temporally and spatially.MethodsA survey was conducted on the kdr alleles at condon 1014 of the VGSC gene and their distributions in 733 specimens of An. sinensis and 232 specimens of the other eight member species of the Anopheles hyrcanus group that were collected from 17 provinces in China in 1996–2014.ResultsA total of three kdr alleles, TTT (F), TTG (F) and TGT (C) were detected, and TGT (C) and TTT (F) were already present in the specimens from Jiangsu and Shandong as early as 1997. The TTT (F) was the most frequent mutant allele, and largely distributed in central China, namely Shandong, Jiangsu, Anhui, Henan, Shanghai, Jiangxi and Hubei. When data were analysed in three time intervals, 1996–2001, 2005–2009, 2010–2014, the prevalence of kdr alleles increased progressively over time in the populations in central China. In contrast, the kdr alleles were less frequent in the samples from other regions, especially in Yunnan and Hainan, despite the documented presence of pyrethroid resistant populations in those regions. Interestingly, no mutant alleles were detected in all 232 specimens of eight other species in the An. hyrcanus group.ConclusionThe survey revealed that the kdr occurrence and accumulation in the An. sinensis populations were more frequent in central China than in the other regions, suggesting that the kdr mutations may contribute significantly to the pyrethroid resistance in the mosquitoes in central China.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0644-0) contains supplementary material, which is available to authorized users.

Highlights

Anopheles sinensis has become an important malaria vector in China
In China, DDT has been widely used for conventional indoor residue sprays (IRS) since 1950s, and pyrethroids have been applied for IRS and insecticide-treated nets (ITNs) since 1980s [12]
The DDT resistance in An. sinensis was documented in Yunnan as early as 1981 [14]; the permethrin resistance was reported in Sichuan in 1989 [15]; and in Fujian in 1989– 1993, resistant populations occurred two years after IRS and ITNs applications, and the resistance spread in more populations three years after applications [13]

Summary

Introduction

The long-term extensive utilization of pyrethroids for ITNs and IRS for mosquito control in the last three decades has resulted in the occurrence of resistant An. sinensis populations in many regions. A positive correlation between the kdr mutation and the resistant phenotype to pyrethroids and DDT was well documented in various Anopheles populations [3,4,5,6,7,8,9,10]. In China, DDT has been widely used for conventional indoor residue sprays (IRS) since 1950s, and pyrethroids have been applied for IRS and insecticide-treated nets (ITNs) since 1980s [12]. These measures have been effective in reducing malaria transmission [13]. The DDT resistance in An. sinensis was documented in Yunnan as early as 1981 [14]; the permethrin resistance was reported in Sichuan in 1989 [15]; and in Fujian in 1989– 1993, resistant populations occurred two years after IRS and ITNs applications, and the resistance spread in more populations three years after applications [13]

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Discussion

Conclusion