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Infectivity variation and genetic diversity among strains of Western equine encephalitis virus

¹ Chemical and Biological Defence Section, Defence Research and Development Canada – Suffield, Box 4000, Station Main, Medicine Hat, AB T1A 8K6, Canada
² United States Army Medical Research Institute of Infectious Diseases, Frederick, MD 21702, USA

Correspondence
Les P. Nagata
les.nagata{at}drdc-rddc.gc.ca

Variation in infectivity and genetic diversity in the structural proteins were compared among eight strains of Western equine encephalitis virus (WEEV) to investigate WEEV virulence at the molecular level. A lethal intranasal infectivity model of WEEV was developed in adult BALB/c mice. All eight strains examined were 100 % lethal to adult mice in this model, but they varied considerably in the time to death. Based on the time to death, the eight strains could be classified into two pathotypes: a high-virulence pathotype, consisting of strains California, Fleming and McMillan, and a low-virulence pathotype, comprising strains CBA87, Mn548, B11, Mn520 and 71V-1658. To analyse genetic diversity in the structural protein genes, 26S RNAs from these eight strains were cloned and sequenced and found to have >96 % nucleotide and amino acid identity. A cluster diagram divided the eight WEEV strains into two genotypes that matched the pathotype grouping exactly, suggesting that variation in infectivity can be attributed to genetic diversity in the structural proteins among these eight strains. Furthermore, potential amino acid differences in some positions between the two groups were identified, suggesting that these amino acid variations contributed to the observed differences in virulence.

The GenBank/EMBL/DDBJ accession numbers for the sequences determined in this work are DQ393791 (Fleming strain), DQ393790 (California), DQ393792 (McMillan), DQ432026 (CBA87), DQ432027 (B11), NC_003908 (71V-1658), DQ393793 (Mn520), and DQ393794 (Mn548).

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