Reisen William K, Fang Ying, Martinez Vincent M
Center for Vectorborne Diseases, Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California, Davis, California 95616, USA.
J Med Entomol. 2006 Mar;43(2):309-17. doi: 10.1603/0022-2585(2006)043[0309:EOTOTT]2.0.CO;2.
Culex tarsalis Coquillett females were infected with the NY99 strain of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) and then incubated under constant temperatures of 10-30 degrees C. At selected time intervals, transmission was attempted using an in vitro capillary tube assay. The median time from imbibing an infectious bloodmeal until infected females transmitted WNV (median extrinsic incubation period, EIP50) was estimated by probit analysis. By regressing the EIP rate (inverse of EIP50) as a function of temperature from 14 to 30 degrees C, the EIP was estimated to require 109 degree-days (DD) and the point of zero virus development (x-intercept) was estimated to be 14.3 degrees C. The resulting degree-day model showed that the NY99 WNV strain responded to temperature differently than a lineage II strain of WNV from South Africa and approximated our previous estimates for St. Louis encephalitis virus (family Flaviviridae, genus Flavivirus, SLEV). The invading NY99 WNV strain therefore required warm temperatures for efficient transmission. The time for completion of the EIP was estimated monthly from temperatures recorded at Coachella Valley, Los Angeles, and Kern County, California, during the 2004 epidemic year and related to the duration of the Cx. tarsalis gonotrophic cycle and measures of WNV activity. Enzootic WNV activity commenced after temperatures increased, the duration of the EIP decreased, and virus potentially was transmitted in two or less gonotrophic cycles. Temperatures in the United States during the epidemic summers of 2002-2004 indicated that WNV dispersal and resulting epicenters were linked closely to above-average summer temperatures.
致倦库蚊雌性成虫感染了西尼罗河病毒（黄病毒科黄病毒属，WNV）的NY99毒株，然后在10至30摄氏度的恒温条件下培养。在选定的时间间隔，使用体外毛细管试验尝试进行传播。通过概率分析估计从摄取感染性血餐到受感染雌性传播WNV的中位时间（中位外在潜伏期，EIP50）。通过将EIP率（EIP50的倒数）作为14至30摄氏度温度的函数进行回归分析，估计EIP需要109度日（DD），且病毒零发育点（x轴截距）估计为14.3摄氏度。所得的度日模型表明，NY99 WNV毒株对温度的反应与来自南非的WNV II系毒株不同，并且接近我们之前对圣路易斯脑炎病毒（黄病毒科黄病毒属，SLEV）的估计。因此，入侵的NY99 WNV毒株需要温暖的温度来进行有效传播。根据2004年流行年份加利福尼亚州科切拉谷、洛杉矶和克恩县记录的温度，每月估计完成EIP所需的时间，并将其与致倦库蚊生殖营养周期的持续时间以及WNV活动的指标相关联。当温度升高后，WNV的地方性活动开始，EIP持续时间缩短，并且病毒有可能在两个或更少的生殖营养周期内传播。2002 - 2004年流行夏季美国的温度表明，WNV的传播以及由此产生的疫情中心与夏季高于平均水平的温度密切相关。
