Reisen W K, Lothrop H D, Chiles R E, Cusack R, Green E G N, Fang Y, Kensington M
Center for Vector-borne Disease Research, School of Veterinary Medicine, University of California, Davis 95616, USA.
J Med Entomol. 2002 Sep;39(5):793-805. doi: 10.1603/0022-2585-39.5.793.
The introduction of a St. Louis encephalitis virus (SLE) genotype new to southeastern California during 2000 was followed by focal enzootic amplification in the Coachella Valley that was detected by seroconversions of 29 sentinel chickens in five of nine flocks of 10 chickens each, isolations of virus from 30 of 538 pools of 50 Culex tarsalis Coquillett females, and collection of 30 positive sera from 2,205 wild birds. This SLE strain over wintered successfully and then amplified during the summer of 2001, with 47 sentinel seroconversions in eight of nine flocks, 70 virus isolations from 719 pools of Cx. tarsalis and Cx. p. quinquefasciatus Say, and 40 positive sera from 847 wild birds. Human illness was not detected by passive case surveillance, despite issuance of a health alert during 2001. Virus amplification during both years was associated with above average temperatures conducive for extrinsic incubation and below average precipitation during spring associated with below average vector abundance. Seroconversions by sentinel chickens provided the timely detection of virus activity, with initial conversions detected before positive mosquito pools or wild bird infections. Vertical infection was not detected among Cx. tarsalis adults reared from immatures collected during the fall-winter of 2000, even though SLE over wintered successfully in this area. Early seroconversions by a sentinel chicken during February 2001 and a recaptured Gambel's quail in April 2001 provided evidence for transmission during winter and spring when ambient temperatures averaged below 17 degrees C, the threshold for SLE replication.
2000年，一种新型圣路易斯脑炎病毒（SLE）被引入加利福尼亚州东南部，随后在科切拉山谷出现局部动物流行病扩大情况，这一情况通过以下方式被检测到：在9群每群10只的鸡中，有5群的29只哨兵鸡出现血清转化；在538组每组50只致倦库蚊（Culex tarsalis Coquillett）雌蚊中，有30组分离出病毒；在2205只野生鸟类中采集到30份阳性血清。这种SLE毒株成功越冬，然后在2001年夏季扩大传播，9群中有8群的47只哨兵鸡出现血清转化，从719组致倦库蚊和致乏库蚊（Culex p. quinquefasciatus Say）中分离出70株病毒，在847只野生鸟类中采集到40份阳性血清。尽管在2001年发布了健康警报，但通过被动病例监测未检测到人类发病情况。这两年病毒的扩大传播与有利于外部潜伏期的高于平均水平的温度以及春季低于平均水平的降水量相关，而春季降水量低于平均水平又与低于平均水平的病媒数量相关。哨兵鸡的血清转化及时检测到了病毒活动，最初的转化在阳性蚊虫样本或野生鸟类感染之前就被检测到。在2000年秋冬采集的未成熟致倦库蚊中饲养的成年致倦库蚊中未检测到垂直感染，尽管SLE在该地区成功越冬。2001年2月一只哨兵鸡以及2001年4月一只重新捕获的甘贝尔鹌鹑早期出现血清转化，为冬季和春季（当时环境温度平均低于17摄氏度，这是SLE复制的阈值）的传播提供了证据。
