Field Efficacy of an Attenuated Infectious Bronchitis Variant 2 Virus Vaccine in Commercial Broiler Chickens

Abstract

Egyptian poultry suffer from frequent respiratory disease outbreaks associated with Infectious Bronchitis Virus (IBV) variant 2 strains (Egy/VarII). Different vaccination programs using imported vaccines have failed to protect the flocks from field challenge. Recent studies confirmed a successful protection using homologous strains as live attenuated vaccines. In this study, a newly developed live attenuated IB-VAR2 vaccine representing the GI-23 Middle East IBV lineage was evaluated in day-old commercial broilers in an IBV-endemic area. A commercial broiler flock was vaccinated with the IB-VAR2 vaccine at day-old age followed by IB-H120 at day 16. The vaccinated flock was monitored on a weekly basis till the slaughter age. The health status and growth performance were monitored, and selected viral pathogen real-time RT-PCR (rRT-PCR) detection was conducted on a weekly basis. Finally, the flock was compared to a nearby farm with only the classical IB-H120 vaccination program. Results showed that the IB-VAR2 vaccine was tolerable in day-old broiler chicks. The IBV virus rRT-PCR detection was limited to the trachea as compared to its nephropathogenic parent virus. Respiratory disease problems and high mortalities were reported in the IB-H120-only vaccinated flock. An exposure to a wild-type Egy/VarII strain was confirmed in both flocks as indicated by partial IBV S1 gene sequence. Even though the IB-VAR2-vaccinated flock performance was better than the flock that received only IB-H120, the IBV ELISA (enzyme-linked immunosorbent assay) and log2 Haemagglutination inhibition (HI) antibody mean titers remained high (3128 ± 2713 and ≥9 log2, respectively) until the 28th day of age. The current study demonstrates the safety and effectiveness of IB-VAR2 as a live attenuated vaccine in day-old commercial broilers. Also, the combination of IB-VAR2 and classical IBV vaccines confers a broader protective immune response against IBV in endemic areas.

Research Note: First evidence of infectious bronchitis virus Middle-East GI-23 lineage (Var2-like) in Germany

“…Therefore, it seems to be very important to find sufficient alternatives for vaccination to improve the protection level. Recently, a new IB-VAR206 vaccine was proven infield to show a good efficacy to protect broilers from clinical illness after exposure to field virus (Elhady et al, 2018). Until now, this vaccine has not been approved in Europe and can thereby only be imported, having a special authorization from the responsible veterinary authorities.…”

A Recombinant La Sota Vaccine Strain Expressing Multiple Epitopes of Infectious Bronchitis Virus (IBV) Protects Specific Pathogen-Free (SPF) Chickens against IBV and NDV Challenges

“…Especially in layer and breeder chickens, a decline in egg production alone can cause significant economic losses. However, IBV and NDV live vaccines probably mutually interfere with concurrent immunization [45][46][47]. Furthermore, a live-attenuated IBV vaccine is at risk of virulence recovery, contributing to emergence of new IBV variants.…”

Protective Efficacy of Different Live Attenuated Infectious Bronchitis Virus Vaccination Regimes Against Challenge With IBV Variant-2 Circulating in the Middle East

“…However, protection studies indicated that homologous strain vaccines usually induce better protection against IBV challenge (23–25). The field situation in Egypt indicates that the IBV variant 2 is the most predominant serotype in Egypt (26–29), hence the newly developed vaccines using the variant 2 strain showed better protection againest homologous challenge under both expermintal and field situation (17, 30). The Egyptian variant-2 viruses shows high genetic difference to all IBV imported vaccines with multiple amino acid substitutions at virus neutralization (VN) epitopes (31–33) that may explain the high frequency of IBV outbreaks in vaccinated flocks in Egypt.…”