Histopathologic Lesion Scoring and Histomorphometric Methods for Measuring Vaccine Reactions in the Trachea of Broiler Chickens

The severity of the tracheal histologic inflammatory response induced in broilers by ocular inoculation of two infectious bronchitis (IBV) and three Newcastle disease virus (NDV) commercial vaccines were evaluated. The vaccines were delivered by eyedrop using a coarse spray on day-1 of age. The vaccines were given individually or in various combinations and were evaluated relative to non-vaccinated controls. Evaluations were performed on post-vaccination (PV) days seven and 14. Histologic endpoints included semiquantitative severity scoring of inflammatory components and quantitative morphometric determinations of inflammatory cell concentration, mucosal thickness, and the percentage of ciliated mucosal surface. Strong positive correlations were observed between routine severity scoring and morphometric inflammatory parameters, while a negative correlation was present between inflammation severity and the percentage of mucosal ciliation. Variable, sometimes extensive, and often statistically significant differences in inflammatory responses were observed between the various vaccines. One IBV-Massachusetts strain vaccine (IBV-A) produced the greatest overall inflammatory response, when given alone or in combination with the NDV vaccines. Enhancement of the tracheitis was seen on PV day 14 by co-vaccination of IBV-A with the NDV vaccines, but not by co-vaccination of IBV-B with NDV. Reduction in cilia percentage was observed for all vaccine groups relative to controls on PV day 7. However, while reactive cilia regeneration occurred on day PV day 14 for most vaccine groups, a cilia regenerative response was not apparent for individual or NDV combination vaccination for IBV-A. The study also demonstrates that substantial microscopic trachea pathology may be present in vaccinated birds not exhibiting apparent clinical respiratory signs.