Avian Reoviruses: Biochemical and Biological Characterization of Some Isolates.

Abstract

The physical, cultural and biochemical properties of avian reoviruses were studied and compared to those of the mammalian reovirus. Analysis of the dsRNA genome by PAGE demonstrated that the avian reovirus can be readily distinguished from the mammalian reovirus by the characteristic migration of on of its genomic dsRNA segments, namely S(,1). Comparison among the various isolates of avian reovirus revealed an extensive polymorphism in the migration pattern of their genome segments. This variability occurred among isolates of different serotypes as well as among isolates within the same serotype. No correlation could be found between genotype and disease state. Examination of the protein composition of avian reoviruses by PAGE revealed the presence of eight structural polypeptides: (lamda)(,A), (lamda)(,B), (lamda)(,C), (mu)(,A), (mu)(,B), (sigma)(,A), (sigma)(,B), and (sigma)(,C). Chymotrypsin treatment of purified virus permitted the localization of polypeptides (lamda)(,A), (lamda)(,B), (lamda)(,C), and (sigma)(,A) to the core by digestion of the outer capsid polypeptides (mu)(,A), (mu)(,B), (sigma)(,B), and (sigma)(,C). Two additional virus-specified, non-structural polypeptides, (mu)(,NS) and (sigma)(,NS), could be demonstrated by immune precipitation of cytoplasmic extract of infected cells. Purified top component fractions exhibited an extra major polypeptide, (sigma)(,Y), not present in virions. Its possible origin and localization within the empty particles are discussed. Unlike their RNA genomes, the various strains of avian reovirus compared demonstrated little polymorphism in regard to the majority of their proteins. Six avian reovirus isolates and a vaccine strain were compared as to virulence, invasiveness and pathological characteristics upon infection of day-old chicks by the foot pad, subcutaneous and oral routes. Pathogenicity varied markedly from 2 x 10('5) pfu/chick to less than 10 pfu/chick for the most virulent isolate. A 6 log difference was demonstrated between the wild type and its vaccine strain virus. All strains revealed, with considerable variation, an arthrogenic potential. No significant differences were noted regarding their ability to spread and invade tissue.