Pathogenicity of avian reoviruses: examination of six isolates and a vaccine strain.

Six avian reovirus isolates and a vaccine reovirus strain were compared for invasiveness, virulence, and pathological characteristics upon infection of day-old specific-pathogen-free chicks by the footpad, subcutaneous, and oral routes of inoculation. No significant differences were noted regarding the ability of individual isolates to infect target tissues. However, virulence (measured as the 50% lethal dose) among the isolates varied markedly from 2 x 10(5) to less than 10 PFU per chick for the most virulent isolate; between the parental wild-type virus and the derivative vaccine virus strain, a million-fold (10(6)) difference in virulence was demonstrated. All strains revealed, with considerable variation, arthrogenic potential.