| Malaria is a potentially fatal disease caused by plasmodium and has serious impacts on human health. Malaria has been effectively controlled in most parts of China. However, sometimes it still outbreaks in Yunnan, Hainan and other areas of China. The malaria increases were seen in the past few years. The most possible reasons were as follows:1) plasmodium developed stronger resistance to common malaria controlling drugs;2) malaria vector, Anopheles population, also produced resistances to pesticides. Up to date, deltamethrin is one of the most popular pesticides with high effectiveness, low toxicity, less residue, easy degradation and other advantages, and has been widely used for vectors control. In recent years, world-wide resistance monitoring showed that the majority of mosquito vectors produced different resistances to the pyrethroid. Anopheles sinensis is one of the dominant mosquitoes in China and is the primary malaria vectors of tertian fever in China and Southeast Asia. Therefore, Anopheles population control is an effective method for malaria prevention, treatment and transmissions. Deltamethrin resistance of An. sinensis has been reported, but the systematic invesitigations of resistances and their mechanisms were still lacking.In this study, deltamethrin resistances of six wide An. sinensis populations and one laboratory colony were tested using WHO drug-membrane interaction method. Furthermore, the pesticide-degrading enzyme activities of GSTs and P450s were detected and pesticide target-site (kdr gene) mutations was also analyzed. The results are as follows:1. Deltamethrin-resistance bioassayThe results showed the corrected mortality of An. sinensis populations from Bishan and Xiushan of Chongqing is32.72%and12.62%, respectively. In Yunnan, the mortality is29.63%for Yuanyang population and38.31%for Mengla population. For Hubei and Hunan population, the mortality is15.34%(Wuxue) and12.88%(Liuyang), All of these populations above showed deltamethrin resistance. As expected, the mortality for laboratory population is98.95%, which is obviously deltamethrin susceptible.2. Metabolic enzymes activity bioassayGSTs enzyme activities are not different among populations from Mengla, Yuanyang, and laboratory population (F=0.297, P>0.05), but significant differences were observed among populations from Xiushan, Bishan, Liuyang and Wuxue (F=36.743,P<0.001). These results revealed that higher GSTs activity was associated with deltamethrin resistance of An. sinensis from Xiushan, Bishan, Liuyang and Wuxue.There were no differences of P450s activities among populations from Liuyang, Wuxue, Xiushan, Bishan and laboratory population (F=0.691, P>0.05); However, significant difference was detected between Mengla and Yuanyang population (F=21.723, P<0.001). It suggested that higher P450s activity contributed to deltamethrin resistance of Mengla and Yuanyang population.3. kdr gene mutation analysisSequence analysis showed one mutation type (TTG→TTT) was detected in the Bishan population, and two mutation types (TTG→TTT/TTC and TTG→TGT) in Xiushan, Wuxue and Liuyang population. But no mutations were obtained in Mengla, Yuanyang and laboratory population. Statistical analysis showed that there was no relationship between gene mutation (TTT) and resistance of Bishan population (χ2=0.2, P=0.6547). Also no association between mutations (TTT:χ2=0.30, P=0.4166; TGT:χ2=0.30, P=0.3833) and resistance of Xiushan population wa sobserved.. Interestingly, significant correlation between mutaions and mortality of WuXue and Liu Yang population were obtained (t=7.79, P<0.01), suggesting that these two mutations in kdr gene were related to deltamethrin resistance. |
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