Reisen W K, Meyer R P, Milby M M, Presser S B, Emmons R W, Hardy J L, Reeves W C
Department of Biomedical and Environmental Health Sciences, School of Public Health, University of California, Berkeley 94720.
J Med Entomol. 1992 May;29(3):472-82. doi: 10.1093/jmedent/29.3.472.
Temporal and spatial patterns of St. Louis encephalitis (SLE) virus transmission were compared at permanent study areas in the southern San Joaquin Valley during years with low (1988 and 1990) and elevated (1989) viral activity. During 1989 and 1990, virus appeared first at sentinel chicken flocks exhibiting low to moderate seroconversion rates at the end of the previous season. This finding, and the early season seroconversion of sentinel chickens at a marsh habitat on 5 March and 2 April 1990, circumstantially indicated that SLE virus may have overwintered on the valley during the winters of 1988-1989 and 1989-1990. The mechanism of overwintering was not elucidated further, because virus could not be isolated from overwintering adult mosquitoes or from immatures collected during the spring. An outbreak of 26 confirmed SLE cases occurred in 1989 during a drought year (rainfall 50% of normal) and followed a spring with elevated temperatures (1.7-3.4 degrees C above normal) and Culex tarsalis Coquillett abundance. Cx. tarsalis was the primary vector, being most abundant during the virus amplification period in early summer and most frequently infected (70 SLE virus positive pools/329 tested). SLE virus also was detected in Culex quinquefasciatus Say (14/65) and Cx. stigmatosoma Dyar (1/4); however, both species were distributed focally and increased in abundance only after widespread seroconversions had occurred in sentinel chickens. Increased virus activity during 1989 was not accompanied by marked changes in vector susceptibility or in SLE virus infectivity for mosquitoes. Decreased virus activity in the Bakersfield area during 1990 could not be attributed to immunity in passeriform birds, because a small seroprevalence survey indicated that few adult birds had antibodies to SLE virus.
在圣华金河谷南部的长期研究区域，对圣路易斯脑炎（SLE）病毒传播的时空模式进行了比较，研究时段包括病毒活动水平较低的年份（1988年和1990年）以及病毒活动水平较高的年份（1989年）。在1989年和1990年，病毒首先出现在前一季末血清转化率低至中等的哨兵鸡群中。这一发现，以及1990年3月5日和4月2日在一个沼泽栖息地哨兵鸡的季初血清转化情况，间接表明SLE病毒可能在1988 - 1989年和1989 - 1990年冬季在该山谷越冬。越冬机制未得到进一步阐明，因为无法从越冬的成年蚊子或春季采集的未成熟蚊子中分离出病毒。1989年，在干旱年份（降雨量为正常水平的50%）爆发了26例确诊的SLE病例，该年春季气温升高（比正常水平高1.7 - 3.4摄氏度）且致倦库蚊数量众多。致倦库蚊是主要传播媒介，在初夏病毒扩增期数量最多，且感染频率最高（329份检测样本中有70份SLE病毒阳性样本）。在致倦库蚊（14/65）和纹腿库蚊（1/4）中也检测到了SLE病毒；然而，这两个物种分布集中，且仅在哨兵鸡广泛发生血清转化后数量才增加。1989年病毒活动增加并未伴随着传播媒介易感性或SLE病毒对蚊子感染性的显著变化。1990年贝克斯菲尔德地区病毒活动减少不能归因于雀形目鸟类的免疫力，因为一项小型血清流行率调查表明，很少有成年鸟类具有SLE病毒抗体。
