Cornel A J, Jupp P G, Blackburn N K
Department of Virology, University of the Witwatersrand, Sandringham, South Africa.
J Med Entomol. 1993 Mar;30(2):449-56. doi: 10.1093/jmedent/30.2.449.
The effects of the extrinsic incubation temperature on the vector competence of Culex univittatus Theobald for West Nile (WN) virus were studied. A mean titer of 7.0 log10 CPD50/ml of mosquito suspension was reached in orally infected mosquitoes after 11, 15, and 16 d of incubation at 26 and 30 degrees C and at fluctuating temperatures in an outside cage (mean temperature, 23.5 degrees C), respectively. In contrast, 22 and 58 d were required to reach the same titers at 18 and 14 degrees C, respectively. Transmission rates of 100% were reached after 58 d (14 degrees C), 22 d (18 degrees C), and 15 and 16 d (30 degrees C and outside). Except at 30 degrees C, transmission rates fluctuated; e.g., at 18 degrees C from day 19, the transmission rate was 80-100%, whereas at 14 degrees C on day 36, the transmission rate was 60% and thereafter 20-100%. The maximum transmission rate occurred concurrently with maximum titers of virus secreted into capillary tubes during in vitro transmission attempts. Mosquito longevity increased as incubation temperature decreased and was maximum at 114 d at 14 degrees C. Mosquitoes that were transferred from 14 to 26 degrees C after 49 d subsequently oviposited, engorged on a pigeon, and transmitted virus, which indicated the possibility for overwintering of WN virus in adult Cx. univittatus. Vector competence at outside cycling temperatures was intermediate between that at 26 and 30 degrees C, indicating that incubation at 26 degrees C would give a fair reflection of the vector competence of Cx. univittatus during the summer near Johannesburg. Two human epidemics of WN virus are reevaluated in the light of these results; it is concluded that, in addition to abnormal rainfall, higher than normal temperatures were important factors for their occurrence.
研究了外在孵育温度对单带库蚊（Culex univittatus Theobald）传播西尼罗河（WN）病毒媒介能力的影响。在26℃和30℃以及室外笼子中波动温度（平均温度23.5℃）下分别孵育11、15和16天后，经口感染的蚊子中蚊子悬液的平均滴度达到7.0 log10 CPD50/ml。相比之下，在18℃和14℃分别需要22天和58天才能达到相同滴度。在58天（14℃）、22天（18℃）以及15天和16天（30℃和室外）后传播率达到100%。除30℃外，传播率有波动；例如，在18℃时从第19天起传播率为80%-100%，而在14℃时第36天传播率为60%，此后为20%-100%。最大传播率与体外传播试验期间分泌到毛细管中的病毒最高滴度同时出现。蚊子寿命随着孵育温度降低而延长，在14℃时最长可达114天。在49天后从14℃转移到26℃的蚊子随后产卵、吸食鸽血并传播病毒，这表明WN病毒在成年单带库蚊中存在越冬的可能性。室外循环温度下的媒介能力介于26℃和30℃之间，这表明在约翰内斯堡附近夏季在26℃下孵育能较好地反映单带库蚊的媒介能力。根据这些结果对两起WN病毒人间疫情进行了重新评估；得出的结论是，除了异常降雨外，高于正常的温度也是疫情发生的重要因素。
