[Similarities and differences between western equine encephalomyelitis viruses with respect to genes for nonstructural protein NSP2 and structural proteins C and E2].

Genetic relationships of geographical isolates of the members of WEE virus serocomplex (McMillan, Fort Morgan, Highlands J, and Y62-33) were assessed by the polymerase chain reaction (PCR) and restriction analysis of the PCR products. Oligonucleotide primers (21 nucleotides in length) were chosen for NSP2, nucleocapsid C, and E2-E1 protein genes based on the known primary structure of the McMillan 16310-5614 genome (L. Uryvayev et al., 1994, 1995). These primers were shown to differentiate well the WEE and SV-like strains of the serocomplex. Y62-33 virus (Udmurtia, Russia) was identical to McMillan strain in three studied regions of NSP2, C, and E2-E1 genes. NSP2 gene could be detected in all the studied geographical isolates and was characterized by the same restriction patterns as endonucleases; it appeared to be the most conservative. The structural genes were less conservative. Fort Morgan virus (Colorado, USA) genome reliably differed from McMillan virus (California, USA) and was negative in PCR with primers to C and E2 gene regions. Highlands J genome (Florida, USA) was positive in PCR with the primers to E2-E1 gene regions but differed from McMillan strain by the nucleocapsid gene. An additional comparative PCR analysis of the C-E2 region in the McMillan and Highlands J genomes showed some, but not complete identity. The origin of these two viruses might be due to the selection of different forms of recombinant viruses. A good correlation of structural genes in PCR and the infectivity neutralization test was noted with the primers and polyclonal antibodies to the closely related strains. High specificity of PCR permits a more accurate detection of the virus origin and relationships.