Mass-like and 1/96 vaccine kinetics evaluation in field and experimental conditions by real-time RT-PCR quantification

Infectious Bronchitis Virus (IBV) is a major issue conditioning poultry farming productivity and management. The applied control strategies deeply vary around the world depending on local epidemiological bases and on practical and cost-linked constraints. In Italy, nearly all the production is held by few companies, which are more often choosing to vaccinate following the protectotype concept, with two heterologous IBV strains co-administrated at one day of life. This managerial decision has many advantages from economical and practical points of view, but it has also been proposed as biologically sustainable by this and other studies. The present work focused on broilers vaccinated with Mass-like and 1/96 strains, demonstrating the persistence of both supplied vaccines along the analysed productive cycles through a longitudinal field study. Particularly, vaccine replication was evaluated by Mass-like and 1/96 specific real-time RT-PCRs through the titre kinetics reconstruction. The same phenomenon was reproduced and verified by a 21 day long experimental study. The vaccine titres presented a common trend of initial increase for the first two weeks and then a steady decrease, fully framed by the experimental study. Titres were still detectable until the productive cycle end in the field trial. Remarkably, the titre reduction was followed by an increase in avian Metapneumovirus (aMPV) and IBV field strain detections. The current study, besides enforcing the epidemiological knowledge of the QX strain prevalence in Italy and the wide aMPV circulation in broilers too, highlights the potential benefits induced by the competing action of vaccine replication against different pathogens.