A new method for testing avian metapneumovirus vaccine efficacy: Evaluation of tracheal ciliary activity after a challenge.

Abstract

Avian metapneumovirus (aMPV) infects turkeys and chickens. It replicates primarily in the upper respiratory tract, causing respiratory disease. Animals may also exhibit lower feed and water consumption and weight loss. Despite the high morbidity and often high mortality associated with aMPV in the field, the pathogenicity of field isolates has been difficult to assess in the laboratory. Usually, only mild respiratory clinical signs with low presentation can be reproduced in experimental infections. Hence, the aim of this study was to develop a simple and reproducible aMPV infection model in chicken, to test vaccines' efficacy. It was hypothesized that the evaluation of ciliary activity of tracheal explants, a parameter used in the evaluation of avian infectious bronchitis vaccines, would be suitable for evaluating aMPV vaccines' efficacy after an experimental challenge. Chickens of commercial origin, with maternally-derived antibodies or SPF chickens were vaccinated at one day of age. Challenges were performed at different ages (17 days to 16 weeks of age). Ciliary activity of tracheal explants was evaluated together with more common parameters of efficacy: clinical signs, body weight gain and serum antibodies. In all cases, the vaccine provided protection against the challenge in terms of ciliary activity. Body weight gain and clinical signs were not suitable in all the experiments for showing efficacy, and a very mild serologic response was observed after vaccination, and only in SPF animals. The results of this study confirmed the working hypothesis: that the ciliary activity of tracheal explants is a suitable method for testing aMPV vaccines in commercial or SPF chickens in ages from 17 days to 16 weeks.