Sellers R F, Maarouf A R
Agriculture Canada, Health of Animals Laboratory Division, Ottawa, Ontario.
Epidemiol Infect. 1988 Dec;101(3):511-35. doi: 10.1017/s095026880002940x.
Information was collected on confirmed outbreaks of western equine encephalitis (WEE) in North America east of the Rockies for 1981 and 1983 (epidemic years) and 1980 and 1982 (non-epidemic years). The initial pattern of outbreaks in Manitoba, Minnesota and North Dakota was determined for each year. Backward (and in some instances forward) wind trajectories were computed for each day 4-15 days (incubation period) before the initial outbreaks of WEE in a given area of province or state. During these years the timing and location of WEE outbreaks in horses and man, seroconversion in chickens, the maximum Culex tarsalis counts at Winnipeg and first isolation of WEE virus from C. tarsalis could be correlated with trajectories of winds from states further south within acceptable intervals. It is suggested that C. tarsalis mosquitoes infected with WEE virus are carried on the wind from Texas on the Gulf of Mexico, where they continue to breed during the northern winter months, to northern Texas and Oklahoma in the spring. In May, June and July C. tarsalis are carried north on southerly winds from these states through Kansas and Nebraska to North Dakota, Minnesota, Wisconsin and Manitoba. Distances of 1250-1350 km are traversed in 18-24 h at heights up to 1.5 km with temperatures greater than or equal to 13 degrees C. Landing takes place where the warm southerly winds meet cold fronts associated with rain. Convergence leads to concentration of C. tarsalis and determines where outbreaks occur. It is possible that return of new generations of C. tarsalis to the south may occur later in the year. The development of an epidemic of WEE in the northern states and provinces would appear to depend on (i) suitable trajectories from the south in June and July with temperatures greater than or equal to 13 degrees C meeting cold fronts with rain, (ii) sufficient C. tarsalis infected with WEE virus at source, carried on the wind and locally, (iii) C. tarsalis biting horses and man, (iv) maintenance of local mosquito populations in August and (v) susceptible hosts (birds) at source and susceptible hosts (horses and man) locally. Possible methods of prediction involving determination of trajectories, identification of C. tarsalis blood meals, measuring seroconversion in calves are discussed in addition to the methods already in use.
收集了1981年和1983年（流行年份）以及1980年和1982年（非流行年份）落基山脉以东北美洲地区确诊的西部马脑炎（WEE）疫情信息。确定了每年马尼托巴省、明尼苏达州和北达科他州的疫情初始模式。计算了在一个省或州的特定区域首次爆发WEE之前4至15天（潜伏期）内每一天的向后（在某些情况下向前）风轨迹。在这些年份里，马和人感染WEE的时间和地点、鸡的血清转化、温尼伯市尖音库蚊的最高数量以及首次从尖音库蚊中分离出WEE病毒，都可以在可接受的时间间隔内与来自更南部各州的风轨迹相关联。有人认为，感染WEE病毒的尖音库蚊在冬季从墨西哥湾的得克萨斯州随风传播，它们在那里继续繁殖，春季再传播到得克萨斯州北部和俄克拉何马州。在5月、6月和7月，尖音库蚊随着南风从这些州向北传播，经过堪萨斯州和内布拉斯加州，到达北达科他州、明尼苏达州、威斯康星州和马尼托巴省。在温度大于或等于13摄氏度的情况下，它们在1.5千米的高度上18至24小时内飞行1250至1350千米。当温暖的南风与伴随降雨的冷锋相遇时，它们就会降落。气流汇聚导致尖音库蚊集中，并决定疫情发生的地点。有可能新一代的尖音库蚊在当年晚些时候会返回南方。北方各州和省份WEE疫情的发展似乎取决于：（i）6月和7月来自南方的合适风轨迹，温度大于或等于13摄氏度，且与伴随降雨的冷锋相遇；（ii）源头有足够数量感染WEE病毒的尖音库蚊随风传播并在当地存在；（iii）尖音库蚊叮咬马和人；（iv）8月当地蚊子数量的维持；（v）源头的易感宿主（鸟类）和当地的易感宿主（马和人）。除了已经在使用的方法外，还讨论了涉及确定风轨迹、识别尖音库蚊血餐、测量小牛血清转化的可能预测方法。
