Reovirus-induced tenosynovitis in chickens: the effect of breed.

The effect of breed of chicken on infection with an arthrotropic avian reovirus strain R2 was studied by oral or footpad inoculation of 1-day-old chicks of the following breeds: (1) specific pathogen-free (SPF) light-hybrid, (2) commercial White Leghorn egg-layer, and (3) commercial Ross I broiler, and observed to 12 weeks of age. Although most inoculated birds of all three breeds developed swelling of one or both legs below the hock joint at 3 to 4 weeks of age, gross lesions of tenosynovitis became progressively more severe and extended above the joints only in broilers, whereas in most orally-infected SPF and commercial light chickens gross lesions were intermittently severe and regressed with time. Cloacal virus shedding continued up to 2 weeks in the lighter breeds and 3 weeks after infection in broilers. From a small proportion of infected chickens, reovirus was also reisolated from heart, pancreas and caecal tonsils. In all breeds, the tissue in which virus persisted longest was the hock joint/tendon. There was a poor correlation between isolation of virus and the presence of gross lesions in chickens of 12 weeks of age, especially in broilers. Virus-neutralisation tests demonstrated that seroconversion in the lighter breeds occurred predominantly at 3 weeks and in broilers at 4 weeks after infection. In all three breeds the footpad infection gave significantly lower growth rates than were found in the control and oral-infection groups. Oral infection had no apparent effect on growth rates. The greater susceptibility of broilers to reovirus infection is discussed.