The use of monovalent or bivalent IBV vaccines significantly reduces clinical signs but not viral load after heterologous challenge

Infectious bronchitis virus (IBV) is an economically significant upper respiratory tract pathogen of poultry. Infection with IBV results in a mild respiratory infection but predisposes chickens to secondary bacterial infections leading to air sacculitis and condemnation at processing. Because of the economic significance of condemnation, nearly all commercial poultry are vaccinated against IBV. Vaccines are effective in a serotype specific manner, meaning they do not induce fully neutralizing antibodies against heterologous serotypes. The major challenge to control is that current vaccines are not effective against novel IBV variants, which seem to arise every few years. Recently, producers have begun to use multiple IBV serotype vaccines given together in an effort to induce cross-protection. This strategy has been used with some success, but variant IB viruses have still been detected in flocks indicating that the vaccine combinations have not prevented infection. In this study, we seek to determine how a single verses a combination of 2 different IBV vaccine types protect against DMV/1639, a currently circulating and economically important IBV variant. For this project, we vaccinated chickens by eye-drop on day of hatch with either a commercial Massachusetts (Mass), Georgia 08 (GA08), or Arkansas (Ark) type IBV vaccine, or with a combination of 2 Mass types, a Mass and GA08, or a Mass and Ark vaccines, and challenged with the variant DMV/1639 virus isolated from a clinical case in Georgia in 2019. Clinical signs were significantly reduced in all vaccinated chickens at 5 days post-challenge however, the DMV/1639 variant virus was detected by RT-PCR and by isolation in embryonated eggs in a majority of vaccinated chickens. Taken together, it seems the cross-protection strategy with these vaccines will aid in reducing or eliminating clinical presentations, but does not prevent infection or replication of the virus. Additionally, it was interesting to note that all vaccines, whether alone or in combination, performed equally in this experiment. In the future, it will be necessary to follow variant IBV viruses in flocks using this cross-protection strategy to evaluate the influence of these vaccines on viral evolution and development of new variants.

Key Words: Infectious bronchitis virus, Vaccine, Cross-Protection.

Abstract presented at the International Poultry Scientific Forum during IPPE 2020.