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Avian reoviruses are ubiquitous among poultry flocks. Although infection is usually present without disease, reoviruses may occasionally be involved in several disease syndromes of which viral arthritis/tenosynovitis in chickens is the most important, particularly in broiler breeds. While reoviruses have been isolated from turkeys and several other species of birds with various conditions, the presence of the virus has been conclusively linked with disease in relatively few instances. In chickens in particular, avian reoviruses with a wide spectrum of pathogenic capability have been isolated and several antigenic types exist. Diagnosis is dependent on the detection of the virus in clinical samples, although the presence of the virus does not necessarily confirm that this is the cause of the disease, except where reoviruses are detected in affected joints. Serological tests are usually difficult to interpret in view of widespread and frequently harmless reovirus infection. The principal approach to control of viral arthritis/tenosynovitis is by vaccination using attenuated vaccines in young birds, followed by inactivated preparations for breeders intended to protect chicks by maternal antibodies. Many vaccines are based on the S1133 strain isolated in the United States of America, but these may not be effective against antigenic variants.

Immunization of breeder chickens by eyedrop with viral arthritis/tenosynovitis vaccine strain S1133 (73rd egg passage) gave no immunity against day-old oral challenge of their progeny at 1 week postvaccination of the breeders, but progeny immunity was observed at 3, 4, 5, 6, and 7 weeks postvaccination of the breeders. Oral cross-challenge of immune progeny with viral isolates from Connecticut, West Virginia, California, Indiana, Pennsylvania, and Minnesota showed that in vitro neutralization of an isolate by anti-S1133 antiserum correlated with in vivo immunity of the progeny against oral day-old challenge with such an isolate.

A viral agent that was isolated from livers of commercial turkey poults that died at approximately two weeks of age was characterized as a reovirus. Experimental infection of day-old chickens with this reovirus isolate resulted in the development of tenosynovitis, hepatitis, and myocarditis. In vitro neutralization of the turkey reovirus isolate by antiserum against chicken reovirus correlated with in vivo protection of maternally immune chickens from day-old oral challenge with the turkey reovirus isolate.

The effect of cyclosporine A on reovirus-infected male broiler chickens was studied. Beginning at 1 or 10 days of age, 3 groups of 15 broilers were injected in the pectoral muscle with 50 mg of cyclosporine A (CSA) in oil per kg body weight every 3 days until 28 days. Controls were injected with olive oil. Two CSA-injected groups and one untreated group were orally infected with 1000 TCID50 of reovirus at 1 day of age. Cell-mediated immunity was evaluated at 17 and 24 days by a delayed-wattle-response test to injected phytohemagglutinin (PHA-M). Cyclosporine A and reovirus significantly (P less than 0.001) depressed the wattle response following the first injection of PHA-M but not the second. At necropsy 28 days postinoculation (PI), no gross lesions were apparent. Histologic lesions in birds infected with reovirus were lymphocytic pericarditis and tenosynovitis; synovial cells were hyperplastic, and heterophils and fibrin were in synovial spaces. Thymic medullary diameters were significantly (P less than 0.001) smaller in all CSA-treated birds. Although CSA suppressed cell-mediated immunity somewhat, there were no apparent differences in severity of microscopic lesions among reovirus-infected groups.

When chicks with maternal antibodies against infectious tenosynovitis (viral arthritis) virus were inoculated orally at 1 day old with tenosynovitis virus, they were protected against developing active tenosynovitis lesions 3 weeks later. They were not protected against subcutaneous inoculation, however. Breeder vaccination against tenosynovitis resulted in immunity of the progeny against oral infection at 1 day old, whereas progeny from unvaccinated breeders were susceptible to such a challenge.