Variation Among Strains of St. Louis Encephalitis Virus: Basis for a Genetic, Pathogenetic, and Epidemiologic Classification

Genetic Variation of Murray Valley Encephalitis Virus

“…Instances of lack of correlation between geographical distribution and genetic variation among flaviviruses have been recorded previously (Trent et aL, 1980;Kerschner et al, 1986;Hori et al, 1986). In those examples however the variant could be traced to another geographical area, was not substantially different, or had ecologically distinct associations.…”

“…5). The relative stability of the genome of MVE is not surprising in view of the findings of Trent et al (1980), who demonstrated genetic stability of the SLE genome in strains circulating for many years in a given geographical region by RNase T1 fingerprint analysis, and the results of McAda et al (1987) and Sumiyoshi et al (1987), who sequenced a large part and the whole of the Japanese encephalitis virus genome respectively, using two different isolates from broadly the same geographical area but isolated about 4 decades apart. The genomes of these two isolates are very similar.…”

Current Research on Dengue

“…In both studies, the virus strains analyzed do not represent all areas of the world where dengue 1 and 2 virus infections occur and, therefore, it is likely that additional genotypic varieties exist. The data suggest that the evolution of dengue virus within a specific geographic region is much slower than that observed for other non-insect-transmitted RNA viruses (44)(45)(46)(47)(48)(49)(50), and, therefore, it may be postulated that the mosquito vector plays an important role in selecting viruses within populations conferring genetic stability on the popUlation of virus transmitted. A second observation relating severity of disease with virus genotype suggests there is no direct relationship between fingerprint type and disease severity; mild to severe disease with hemorrhagic symptoms and shock have been associated with viruses having almost identical fingerprint patterns (D.W. Trent, personal communication).…”

Pathobiology of the Flaviviruses

“…The biological characteristics of SLE virus strains were related to genetic analyses by Trent et al (1980Trent et al ( , 1981. On the basis of similarity among oligonucleotide fingerprints, 57 virus strains from North America could be classified into three "topotypes," representing different geographic areas (the Ohio-Mississippi Basin, Florida, and the western United States) and virus-vector relationships (c. pipiens, C. nigripalpus, and C. tarsalis, respectively).…”

“…As measured by DTH, leukocyte-migration inhibition, and adoptive transfer of cells, CMI responses are relatively shortlived after primary infection , but memory functions and secondary CMI responses have not been studied. Heterologous cross-protection among flaviviruses has been extensively investigated (Vorndam, 1980), and its molecular basis has been explored using monoclonal antibodies (Roehrig et al, 1983). While antibodies appear to play the principal role in cross-protection, cellular immunity and interference phenomena may also be involved.…”