Effect of infection route and concurrent infectious bronchitis virus vaccination on Mycoplasma gallisepticum disease pathology in an experimental model

The study of Mycoplasma gallisepticum (MG) infection is needed, not only to understand the disease process but also to understand the mechanisms by which MG vaccines protect the host. Many model systems have been used to study the MG disease process. This work compared two different routes of infection (intratracheal versus eye drop) in commercial pullets, looking for differences in the pathology (air sac and tracheal lesion scores, and tracheal mucosal thickness) and the humoral immune response (measured by serum plate agglutination) of the host. The impact of concurrent infectious bronchitis virus vaccination on disease outcomes was also determined. Results showed that the intratracheal route of MG infection caused increased air sac and tracheal lesion scores and tracheal mucosal thickness at one week post infection, whereas the eye drop route produced no noticeable pathology. However, tracheal mucosal thicknesses of intratracheally challenged pullets were not statistically different from those of the eye drop challenged or control pullets at two and three weeks post infection. Concurrent infectious bronchitis virus vaccination had a negligible outcome on disease pathology. Vaccination of specific-pathogen-free chickens with the F-strain MG vaccine completely protected them against the effects of MG intratracheal infectious challenge, as evidenced by a lack of significant difference in air sac and tracheal lesion scores and tracheal mucosal thickness with those of unchallenged media control chickens.