Avian pneumovirus infection of laying hens: Experimental studies

Abstract

Administration of a virulent strain of avian pneumovirus (APV) to specific pathogen free laying hens by the oculonasal route failed to induce a drop in egg production or any adverse effects on eggshell quality. However, intravenous (i.v.) inoculation of the same strain caused a substantial drop in egg production and a high incidence of soft and thin-shelled eggs. Some respiratory 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 epithelium up to 9 days p.i. This challenge model was then used to investigate the efficacy of live attenuated turkey rhinotracheitis (TRT) vaccine administered alone at 1 day old, or an inactivated TRT vaccine (at 16 weeks), or a combined programme using both vaccines, in protecting against this challenge. Neither the live nor the inactivated vaccine alone protected against clinical signs (respiratory infection or diarrhoea). However, the inactivated, but not the live, vaccine did protect against the effect of the i.v. challenge on laying performance. In contrast, the combined vaccination programme protected completely against both clinical signs and poor egg-laying performance. 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 necessary to provide complete protection of laying chickens against APV challenge.

Detection and differentiation of avian pneumoviruses (metapneumoviruses)

“…Interestingly, immunochemical methods have been used to demonstrate APV-specific antigen in the female reproductive tract following experimental inoculation. Jones et al (1988) used IF to demonstrate specific staining of the uterus of experimentally inoculated laying turkeys, while Cook et al (2000) used IP to demonstrate APV-specific staining in the oviduct of experimentally inoculated laying hens. However, the short time for which APV antigen has been detected by these methods in experimentally inoculated birds (Majó et al, 1995;Catelli et al, 1998) suggests the need for caution when using antigen detection methods to attempt to diagnose APV infection in laying birds, since a negative result may not indicate absence of infection.…”

“…Furthermore, the type of anti-APV antibody used to prepare the conjugate varies considerably. For example, Jones et al (1988) used a convalescent serum raised in APV-free turkeys, while and Majó et al (1995) used a hyperimmune rabbit antiserum and Catelli et al (1998) and Cook et al (2000) used a mouse-anti-TRT mAb. These differences also make comparisons of results between different laboratories, and therefore decisions on the optimal conditions to recommend, very difficult.…”

Drop of Egg Production in Chickens by Experimental Infection with an Avian Metapneumovirus Strain PLE8T1 Derived from Swollen Head Syndrome and the Application to Evaluate Vaccine

“…Our observation suggested that aMPV that is known to have respiratory virulence also could have virulence to reproductive organs. A drop in egg production induced by experimental challenge of chickens with aMPV was reported [6]; however, the aMPV strain used in the challenge was the one isolated from chickens showing an egg drop [3]. Therefore, this is the first report on reproduction of an egg drop in chickens by an aMPV isolated from chickens showing only respiratory symptoms.…”

“…Nevertheless, this strain, when inoculated intravenously, did not induce any respiratory symptoms but only the effect on egg production with gross lesions in the uterus was observed in the present experiments. It was thought that intravenous inoculation may provide a useful system in evaluating the effect on egg production as previously described [6].…”

“…Experimental infection of laying hens by intravenous route with a virulent aMPV strain isolated from chickens exhibiting a drop in egg production could successfully induce a drop in egg production in the challenged birds [6]. Similar experiments with other aMPV strains have not been reported so far.…”