the liver were present. There have also been approaches to identify avian reoviruses molecularly by observing infected tissues with dot-blot hybridization, PCR, and a combination of PCR and RFLP. This combination allows for the reovirus strain to be typed. Prevention Vaccines are available (ATCvet codes: for the inactivated vaccine, for the live vaccine, plus various combinations). Given that avian reovirus infections are widespread, the viruses are relatively resistant outside the host, and that vertical and horizontal transmission occurs, eradicating avian reovirus infection in commercial chicken flocks is very unlikely. In addition, absence of detectable seroconversion and failure to detect virus in cloacal swabs are unreliable indicators of resisting infection, or transmission via the egg. Thus, the most proactive and successful approach to controlling this disease is through vaccination. Since chicks are more prone to being detrimentally affected by the disease right after hatching, vaccine protocols that use live and killed vaccines are designed to provide protection during the very early stages of life. This approach has been accomplished through active immunity after early vaccination and a live vaccine or passive immunity from maternal antibodies followed with vaccination of the breeder hens. Currently, efforts toward administering inactivated or live vaccines to breeding stock to allow passive immunity to the offspring via the yolk are being taken. Epidemiology Avian reovirus can be transmitted both vertically and horizontally. Egg transmission has been observed after experimental infection, however the rate of transmission is very low. Congenitally infected chicks are assumed to act as a nucleus of infection for the rest of the hatch due to their high probability of becoming infected through the fecal-oral route or through the respiratory tract. Infection may also enter through the exposure of broken skin of the feet or legs of the chickens, where it then can become established in the hock joints. Once the infection has entered the body, avian reovirus can survive in the tissues of chickens for many weeks. Resistance to reovirus infections in chickens is directly related to age. Chicks that are infected one day after birth are more prone to experimentally synthesized tenosynovitis/arthritis than those that were infected at two weeks or older. Chicks that were infected a day after birth also displayed a development of more severe joint lesions and higher intestinal virus titers than those who were infected at two weeks of age. Infectious agents, which increase the pathogenicity of reovirus in