The RTV1 genome contained 8094 nucleotides and had approximately 95% identity with another rat theilovirus, NSG910, and 73% identity with TMEV strains. feces at 14 d postinoculation, at which time 40% of CD rats were fecal positive. By 56 d postinoculation only 20% of CD rats had detectable RTV serum antibodies. Our data provide additional sequence information regarding a rat-specific and indicate that SD rats are more susceptible than CD rats to RTV1 infection. that is antigenically similar to Theiler murine Rabbit Polyclonal to PGCA2 (Cleaved-Ala393) encephalomyelitis virus AN3199 (TMEV) of mice.4,6,10,12,13,20 Recent reports on the prevalence of antibodies in rats to this vary from approximately 0.6% of sera tested from research rats in North America10 to 54.4% in a survey of 18 Brazilian research facilities.3,6,20 Multiple designations have been used to identify the that infects rats, including Theiler-like virus of rats,13 Theiler murine encephalomyelitis virus (TMEV),20 rat enterovirus,1 rat encephalomyelitis virus,7 rat cardiovirus,15 and recently rat theilovirus.2 We have elected to refer to the virus as rat theilovirus (RTV), consistent with 1 of the cited references,2 to indicate the relation AN3199 of the rat virus to TMEV of mice and to identify it as a rat-specific agent. The first report of natural infection of rats with a was in 1964 with the discovery of MHG virus.12 The finding resulted from an isolated observation in which a few rats in a large research colony displayed clinical signs indicative of central nervous system deficits, including incoordination, torticollis, circling, and tremors. The MHG virus recovered from infected rats was antigenically crossreactive with TMEV strain GDVII and had physical properties consistent with viruses in the family. The virus was propagated in cell culture, and neurologic disease was reproduced when virus was inoculated into suckling mice and suckling rats.12 Subsequent serologic studies using crossneutralization, complement fixation, and hemagglutination inhibition assays further substantiated the antigenic relatedness between MHG virus and multiple strains of TMEV.4,11 In addition, sera from normal rats contained antibodies to the newly identified Theiler-like virus of rats, suggesting widespread infection of the virus in research rat colonies.12 More recently in Japan, a Theiler-like virus was isolated after intracranial inoculation of newborn Wistar rats with intestinal homogenates from TMEV GDVII-seropositive rats.13 Inoculated rats did not develop clinical signs of infection, but virus was cultivated in BHK21 cells from brain homogenates of the 10-d-old Wistar rats inoculated intracranially. Physiochemical properties of the virus, designated NSG910, were consistent with those of the genus. Sequence analysis also showed that NSG910 was a in the family that was related to, but distinct from MHG virus, and strains of TMEV. This report served to further document the existence of a unique of rats closely related to, but distinct from, TMEV AN3199 strains.13 In a recent report from Brazil, neonatal mice and rats inoculated with intestinal homogenates from rats with antibodies to TMEV strain GDVII developed neurologic signs of flaccid hindlimb paralysis and tremors. In addition, brain homogenates from the affected animals were positive by RT-PCR for cardioviral RNA.20 Picornavirus virions are approximately 30 nm in diameter, nonenveloped, with icosahedral symmetry and a single-stranded, positive-sense RNA genome.19 and are 2 species of in the family. species includes mengovirus, Maus Elberfeld virus, and Columbia.