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Characterisation of avian reoviruses

Robertson, Martin Dennis (1986) Characterisation of avian reoviruses. PhD thesis, Murdoch University.

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Avian reoviruses have been associated with a wide variety of diseases in poultry, including tenosynovitis and a runting/stunting syndrome. This thesis describes an investigation of outbreaks of tenosynovitis and the runting/stunting syndrome in commercial poultry in Australia, the isolation and characterisation of avian reoviruses from affected chickens, and attempts to reproduce the 2 disease syndromes with the isolated viruses.

The histopathological lesions observed in tenosynovitis-affected chickens were confined to the tendons, tendon sheaths and peritendinous tissues of the hock region and consisted of a marked inflammatory reaction with mononuclear cell and heterophil infiltration of affected tissues. The runting/stunting syndrome of broiler chickens was clinically characterised by marked reduction in growth rates and pathologically by thymic atrophy, and atrophy and degeneration of the pancreas. Avian reoviruses were isolated from affected chickens in the majority of outbreaks of both diseases. Virus was recovered from 13% of tenosynovitis-affected chickens, 62% of runted/stunted chickens, and from 76% of normal chickens of the same age as those examined with the runting/stunting syndrome.

Avian reoviruses isolated from affected and normal chickens antigenically heterogenous but were assigned to 3 antigenic groups based on the results of reciprocal serum were neutralisation tests. It was not possible to associate a particular antigenic type with either tenosynovitis or the runting/stunting syndrome. Studies of the electrophoretic migration profiles of the genomic RNA segments by sodium dodecyl sulphate polyacrylamide gel electrophoresis also revealed extensive heterogeneity of the isolated reoviruses. No specific genome type could be associated with any particular disease syndrome or antigenic type. Extensive variation in the genomic migration patterns was detected in isolates from different flocks of chickens and the existence of more than one genome type within individual flocks was also demonstrated.

The pathogenicity of the isolated viruses for specific pathogen-free (SPF) chickens was low. Foot pad inoculation of SPF chickens with reoviruses isolated from tenosynovitis-affected birds resulted in mild microscopic lesions involving only the inoculated leg. No histopathological changes were observed in chickens inoculated orally. A variation in pathogenicity of reovirus isolates and an age-linked susceptibility of chickens to reovirus infection was demonstrated. No growth retardation or microscopic lesions were produced in SPF chickens inoculated orally with tissue homogenates prepared from runted chickens or with reoviruses isolated from affected chickens.

Serological studies of antibodies to reovirus, adenovirus, infectious bursal disease virus (IBDV) and reticuloendotheliosis virus (REV) in chickens from outbreaks of the disease syndromes were conducted. In the 2 tenosynovitis outbreaks examined, antibodies to avian reovirus were detected in all chickens examined although the serological response differed in the 2 outbreaks. A hypothesis to explain this difference was proposed. There was no serological evidence to suggest that adenoviruses, IBDV, Mycoplasma gallisepticum or M. synoviae were associated with tenosynovitis. In 4 outbreaks of the runting/stunting syndrome, antibodies to reovirus were not detected in the 3-week-old affected chickens which suggested that the chickens were either infected after 2 weeks of age or that antibody production as a result of earlier infection may have been suppressed, perhaps by maternally-derived antibody. There was no serological evidence to suggest that IBDV, REV or adenovirus were involved in the runting/stunting syndrome.

The results obtained were consistent with the hypothesis that some strains of avian reoviruses are a cause of subclinical tenosynovitis lesions in chickens but that the development of clinical tenosynovitis is due to the occurrence of secondary infection by bacteria, particularly Staphylococcus aureus. While reoviruses were commonly isolated from chickens with the runting/stunting syndrome they were also commonly present in normal chicken flocks and there was no evidence to prove that they were causal agents of the runting/stunting syndrome.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary Studies
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Wilcox, Graham and Pass, David
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