The regime of administering the infectious bronchitis (IB) Ma5 vaccine (Massachusetts serotype) at 1 day old and the heterologous 4/91 vaccine at 2 weeks of age, was shown to be highly effective in protecting the respiratory tract of speci® ed pathogen free chickens. Protection, as measured by assessing ciliary activity of the tracheal epithelium following challenge, was excellent against challenge at 5 weeks of age with IB strains of many serotypes, isolated from disease outbreaks in different parts of the world. This vaccination protocol was more effective than revaccination with a vaccine of the same serotype as the ® rst vaccine. Furthermore, signi® cantly better protection was seen when the Ma5 vaccine was given before, rather than at the same time as or following, the 4/91 vaccine.It is suggested that the use of these two IB vaccines will frequently broaden the protection possible against challenge with IB isolates of many different serotypes, without the need to develop a new IB vaccine to combat each new IB serotype that emerges.

A subgroup B isolate of turkey rhinotracheitis virus (TRTV) or avian pneumovirus (APV), obtained from a flock of commercial breeding chickens experiencing poor egg production, mortality and swollen head syndrome, was shown to cause substantial respiratory signs in both young SPF chickens and chicks with high levels of maternally derived TRT antibodies.This isolate replicated to high titre in the respiratory tract of experimentally inoculated SPF chickens for approximately 5 days after inoculation, but was recovered only occasionally after that time. It was never recovered from non-respiratory tract tissues. A detailed, sequential histological and immunoperoxidase study was performed. This revealed that, whilst TRT virus could be demonstrated consistently in the epithelium of upper respiratory tract tissue, although only for a short time after inoculation, the damage which it caused was minimal and recovery was rapid. This study, using a pathogenic TRT isolate obtained from diseased chickens, provides clear evidence that TRT virus can cause damage to the respiratory tract of chickens and that this damage is both localized and short lived.

On the basis of virus isolation and the demonstration of specific neutralising antibody in sera, infectious bronchitis virus (IBV) 4/91 (commonly called 793B) has been shown to be present in broiler, breeder and layer flocks of chickens in many parts of western Europe and also in Thailand and Mexico. These flocks had all been vaccinated against infectious bronchitis and the need for improved methods to control this new virus, still prevalent at least four years after it was first isolated, is discussed.

No abstract

The experimental inoculation of 38-week-old turkey hens with a pool of field isolates of turkey rhinotracheitis virus (TRTV) induced a marked respiratory infection and a substantial drop in egg production. Administration of a live-attenuated TRT vaccine at 1 week of age did not protect the layers against respiratory infection, but provided good protection against the effects of challenge on laying performance. However, a combination of live priming followed by injection of inactivated vaccine provided excellent protection against both respiratory infection and drops in egg production.

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.

Avian nephritis virus (ANV) strain G-4260 was inoculated orally in to 1-day-old and 3-week-old chickens and the sequential antibody response to the virus was monitored by serum neutralization, ELISA and immunofluorescence tests. The order of sensitivity of the serological tests was in the sequence given above, with the neutralization test being by far the most sensitive. There was no obvious difference in the antibody titres produced by either age group. Virus was recovered from kidney tissue, the highest titres being obtained 3 to 5 days post-inoculation. Histological examination revealed mainly lymphocytic infiltration of the interstitium and degenerative changes in the tubular epithelium of the kidney. The G-4260 strain of ANV was given orally to 1-day-old turkey poults, but no serological response was induced. Virus was not recovered from the kidneys and no histological lesions were produced in this organ. Monoclonal antibodies were produced which neutralized the infectivity of ANV. An antigen trap ELISA was developed using a monoclonal antibody and infected chicken kidney tissue cultures. However, this assay did not detect ANV in kidney samples taken directly from infected chickens, with the exception of one sample which was shown to contain thehighest concentration of infectious virus.