John Rubaihayo, Ephraim Tukesiga, Andrew Abaasa
Public Health Department, Mountains of the Moon University, POBox 837, Fort-Portal, Uganda.
Malar J. 2008 May 26;7:92. doi: 10.1186/1475-2875-7-92.
Pyrethroid insecticide-treated mosquito nets are massively being scaled-up for malaria prevention particularly in children under five years of age and pregnant mothers in sub-Saharan Africa. However, there is serious concern of the likely evolution of widespread pyrethroid resistance in the malaria vector Anopheles gambiae s.l. due to the extensive use of pyrethroid insecticide-treated mosquito nets. The purpose of this study was to ascertain the status of pyrethroid resistance in An. gambiae s.l. in western Uganda.
Wild mosquitoes (1-2 days old) were exposed in 10 replicates to new nets impregnated with K-othrine (Deltamethrin 25 mg/m2), Solfac EW50 (Cyfluthrin 50 mg/m2) and Fendona 6SC (Cypermethrin 50 mg/m2) and observed under normal room temperature and humidity (Temperature 24.8 degrees C-27.4 degrees C, Humidity 65.9-45.7). A similar set of mosquitoes collected from the control area 80 km away were exposed to a deltamethrin 25 mg/m2 impregnated net at the same time and under the same conditions. The 10-year mean KDT50 and mortality rates for each of the three pyrethroid insecticides were compared using the Student t-test.
A significant increase in the mean knockdown time (KDT50) and mean mortality rate were observed in almost all cases an indication of reduced susceptibility. The overall results showed a four-fold increase in the mean knockdown time (KDT50) and 1.5-fold decrease in mortality rate across the three pyrethroid insecticides. There was a significant difference in the 10-year mean KDT50 between deltamethrin and cyfluthrin; deltamethrin and cypermethrin, but no significant difference between cyfluthrin and cypermethrin. The 10-year mean difference in KDT50 for mosquitoes exposed to deltamethrin from the control site was significantly different from that of mosquitoes from the intervention site (p<0.05, t=3.979, 9df). The 10-year mean difference in mortality rate between deltamethrin (84.64%); cyfluthrin (74.18%); cypermethrin (72.19%) and the control (90.45%) showed a significant decline in mortality across all the three insecticides.
Generally the results showed a trend of increase in mosquito resistance status with cross-resistance against all the three pyrethroid insecticides. This study reveals for the first time the development of pyrethroid resistance in An. gambiae s.l. in Western Uganda. It is therefore strongly recommended that the impact of this development on malaria control efforts be closely monitored and alternative fabric treatments be considered before this problem curtails community wide implementation of this malaria control strategy in Uganda.
拟除虫菊酯杀虫剂处理过的蚊帐正在大规模推广用于预防疟疾，尤其是在撒哈拉以南非洲地区五岁以下儿童和孕妇中。然而，由于拟除虫菊酯杀虫剂处理过的蚊帐的广泛使用，人们严重担心疟疾媒介冈比亚按蚊复合种（Anopheles gambiae s.l.）可能会广泛产生拟除虫菊酯抗性。本研究的目的是确定乌干达西部冈比亚按蚊复合种的拟除虫菊酯抗性状况。
将1 - 2日龄的野生蚊子分成10组，暴露于浸有凯素灵（溴氰菊酯25毫克/平方米）、锐劲特EW50（氟氯氰菊酯50毫克/平方米）和奋斗呐6SC（氯氰菊酯50毫克/平方米）的新蚊帐中，并在正常室温和湿度（温度24.8摄氏度 - 27.4摄氏度，湿度65.9 - 45.7）下观察。同时，在相同条件下，将从80公里外的对照区域收集的一组类似蚊子暴露于浸有25毫克/平方米溴氰菊酯的蚊帐中。使用学生t检验比较三种拟除虫菊酯杀虫剂各自的10年平均击倒时间（KDT50）和死亡率。
几乎在所有情况下，平均击倒时间（KDT50）和平均死亡率均显著增加，这表明敏感性降低。总体结果显示，三种拟除虫菊酯杀虫剂的平均击倒时间（KDT50）增加了四倍，死亡率降低了1.5倍。溴氰菊酯与氟氯氰菊酯、溴氰菊酯与氯氰菊酯之间的10年平均KDT50存在显著差异，但氟氯氰菊酯与氯氰菊酯之间无显著差异。来自对照地点暴露于溴氰菊酯的蚊子的10年平均KDT50差异与干预地点的蚊子的差异显著不同（p<0.05，t = 3.979，9自由度）。溴氰菊酯（84.64%）、氟氯氰菊酯（74.18%）、氯氰菊酯（72.19%）与对照（90.45%）之间的10年平均死亡率差异表明，所有三种杀虫剂的死亡率均显著下降。
总体而言，结果显示蚊子抗性状况呈上升趋势，对所有三种拟除虫菊酯杀虫剂均有交叉抗性。本研究首次揭示了乌干达西部冈比亚按蚊复合种中拟除虫菊酯抗性的发展情况。因此，强烈建议密切监测这一发展对疟疾控制工作的影响，并在这一问题阻碍乌干达社区广泛实施这一疟疾控制策略之前考虑采用替代的织物处理方法。
