Protective Efficacy of Different Live Attenuated Infectious Bronchitis Virus Vaccine Combination against Challenge with GI11 (BR-Type) Strain

Abstract

The infectious bronchitis virus (IBV) is an avian coronavirus that causes a highly contagious disease that results in substantial economic losses to the poultry industry worldwide. The prevention is mostly based on biosecurity measures and vaccination. The vaccination programs are defined by epidemiological status and cross-immunity provided against different serotypes. Programs using vaccine combinations can be designed to increase protection. We conducted an experimental study to compare two vaccine programs on protection against a virulent strain belonging to the GI-11 genotype (BR-type) isolated in Brazil using two different Mass-type vaccines combined with a BR-type live vaccine. Two groups of commercial chicks were vaccinated at day-1 using two commercially available Mass-type vaccines + BR-type vaccine. They were challenged intranasally at 28-day using 104 EID50/0.1 microliter/chick of wild-type G11 IBV (IBV/24W). Ciliostasis, macroscopic and microscopic lesion scores were evaluated at 4 and 11-days post vaccination (dpv) and 5 days post infection (dpi) and not showed differences between vaccinated groups. MLV+BR-Type group presented highest amount of BR strain vaccine and lowest amount of Mass strain vaccine in tracheal and cloacal swabs at 4 and 11 dpv. In the other hand, the Ma5+BR-type group showed fewer BR-type positive in both samples tested. After challenge, MLV+BR group showed higher titer of antibody measured by ELISA. These results suggest that the selection of a Mass-type vaccine strain can impact directly in the BR vaccine replication, when used associated, and consequently the induction of humoral immune response. Despite that, both protocols provided protection against the challenge with G11 strain.