Avian pneumovirus infection of laying hens: experimental studies

Administration of a virulent strain of avian pneumovirus (APV) to specific pathogen free laying hens by the oculonasal route failed to induce a drop i n egg production or any adverse effects on eggshell quality. However, intra venous (i.v.) inoculation of the same strain caused a substantial drop in e gg production and a high incidence of soft and thin-shelled eggs. Some resp iratory signs were also observed and the hens appeared sick, with diarrhoea being observed in approximately one-half of the hens between 4 and 11 days post-inoculation (p.i.). APV antigen was detected in the oviduct epitheliu m up to 9 days p.i. This challenge model was then used to investigate the e fficacy of live attenuated turkey rhinotracheitis (TRT) vaccine administere d alone at 1 day old, or an inactivated TRT vaccine (at 16 weeks), or a com bined programme using both vaccines, in protecting against this challenge. Neither the live nor the inactivated vaccine alone protected against clinic al signs (respiratory infection or diarrhoea). However, the inactivated, bu t not the live, vaccine did protect against the effect of the i.v. challeng e on laying performance. In contrast, the combined vaccination programme pr otected completely against both clinical signs and poor egg-laying performa nce. This protection lasted until at least 60 weeks of age. On the basis of the results with this experimental model, it is concluded that the use of live priming followed by administration of inactivated TRT vaccine is neces sary to provide complete protection of laying chickens against APV challeng e.