Kramer L D, Fallah H M
Center for Vector-Borne Disease Research, School of Veterinary Medicine, Department of Pathology, Microbiology, Immunology, University of California, Davis 95616, USA.
Am J Trop Med Hyg. 1999 Apr;60(4):708-13. doi: 10.4269/ajtmh.1999.60.708.
The mechanism for long-term maintenance of western equine encephalomyelitis (WEE) virus in California was investigated by studying genetic variation in the E2 portion of the genome of 55 strains of WEE virus isolated since 1938 from different locations in California. Four major lineages were evident: virus strains isolated from the Central Valley since 1993 and Los Angeles in 1991 formed lineage A; southern California strains isolated since 1978 and isolates from the Central Valley from 1978 to 1987 formed lineage B; northern California isolates from 1968 to 1971 formed lineage C; and early isolates from 1938 to 1961 formed a fourth lineage, D. The separation of strains from north and south of the Tehachapi and San Bernardino Mountains (i.e., the Central Valley and southern California, respectively) since 1991 indicates that there has been little recent movement of virus between the two regions and recent strains from these two locations appear to be evolving independently. However, within the Central Valley and within southern California, virus appears to circulate freely, perhaps by movement of birds or mosquito vectors. Although the current virus lineage in the Central Valley may have been introduced from an unknown source in 1991, introduction and establishment of new viral genotypes from outside California do not seem to occur regularly. It appears most likely that virus is maintained in separate geographic areas of California through local persistence in enzootic foci.
通过研究自1938年以来从加利福尼亚不同地点分离出的55株西部马脑炎（WEE）病毒基因组E2部分的基因变异，对该病毒在加利福尼亚长期维持的机制进行了调查。明显有四个主要谱系：1993年以来从中部山谷分离出的病毒株以及1991年从洛杉矶分离出的病毒株形成了谱系A；1978年以来从南加利福尼亚分离出的毒株以及1978年至1987年从中部山谷分离出的毒株形成了谱系B；1968年至1971年从北加利福尼亚分离出的毒株形成了谱系C；1938年至1961年的早期分离株形成了第四个谱系D。自1991年以来，从蒂哈查皮山和圣贝纳迪诺山以北和以南（即分别为中部山谷和南加利福尼亚）分离出的毒株表明，这两个地区之间最近几乎没有病毒传播，而且来自这两个地点的近期毒株似乎在独立进化。然而，在中部山谷和南加利福尼亚内部，病毒似乎可以自由传播，可能是通过鸟类或蚊媒的移动。尽管中部山谷目前的病毒谱系可能是1991年从一个未知来源引入的，但从加利福尼亚以外引入并建立新的病毒基因型似乎并不经常发生。看起来最有可能的是，病毒通过在地方性疫源地的局部持续存在而在加利福尼亚的不同地理区域得以维持。
