Developing Novel Vaccines to Protect Poultry Against Infectious Bronchitis

October 10, 2017

Editor’s Note: The infectious bronchitis virus (IBV) of the Arkansas type is widespread and common in the U.S. poultry industry. It’s impact to the consumer is large as it causes the chicken to have a reduced feed conversion rate, lower weight gain, and it results in more rejects (condemnations) at slaughter. Auburn College of Veterinary Medicine scientists in the Department of Pathobiology are working on the development of novel vaccines to more effectively prevent this respiratory disease and in doing so, help to hold down the cost of poultry meat and eggs for the consumer. The following blog talks about the importance of this research and describes the work of a CVM team headed by Drs. Haroldo Toro and Vicky L. van Santen.

Developing Novel Vaccines to Protect Poultry against Infectious Bronchitis

Dr. Haroldo Toro and Dr. Vicky L. van Santen

Poultry meat and eggs constitute the most important protein source for human consumption worldwide. Preventing viral diseases in commercial poultry assists in maintaining the cost of poultry products at an affordable level for the consumer. Auburn University College of Veterinary Medicine researchers, along with colleagues at USDA’s Southeast Poultry Research Laboratory, has been working on the development of novel vaccines to protect chickens against infectious bronchitis, a viral disease continuously causing enormous losses in poultry meat and egg production worldwide.

Vaccine development for commercial chicken flocks poses significant challenges. Among others, the cost of the vaccine should not significantly increase the price of poultry products to the consumers, and mass administration to hundreds of thousands of chickens must be feasible and cost effective.

In the U.S. infectious bronchitis virus (IBV) of the Arkansas type is highly prevalent in the broiler industry despite extensive vaccination with commercially available vaccines. Abundant scientific evidence indicates that current Arkansas IBV live vaccines provide a source for the emergence of novel viruses that perpetuate IBV infection in poultry houses. Our efforts to improve vaccines to protect poultry against IBV include the following strategies:

• Increasing the uniformity of the virus in the currently available IBV Arkansas-type live vaccines. We have previously shown that the viruses in current Arkansas IBV vaccines, referred to collectively as a virus population, are vastly diverse, just like a human population in which not all individuals look and act the same. Some of the viruses in the vaccines multiply better in chickens, causing damage to the respiratory tract and perhaps becoming more virulent as they are passed among the chickens in a flock. Our vaccine candidate with increased homogeneity lacks these viruses that multiply better in chickens. Furthermore, our work has shown that a more homogeneous vaccine population seems to provide a better target to the immune system. This improved vaccine candidate confers effective protection against IBV and reduces emergence of virulent viruses. We are currently investigating the qualitative and quantitative nature of the immune responses induced that would explain why vaccination with this more homogenous vaccine virus population (unlike the currently available heterogeneous vaccine) prevents emergence of variants arising from both IBV vaccine viruses and IBV infecting vaccinated chickens. Furthermore, we are testing the vaccine candidate at an outside commercial laboratory to confirm our previous results.
• Measuring protection conferred by vaccination is performed by different methods. Determining the amount of virus present in the upper respiratory tract of vaccinated chickens after experimental infection with virulent virus is a common procedure. The photo shows collection of lachrymal fluid to determine viral load.

Development of a recombinant vaccine against IBV expressing a more conserved portion of the infectious bronchitis virus attachment protein than has traditionally been used for novel IBV vaccine strategies. Using molecular genetics tools, we transformed a harmless virus to show a characteristic portion of a virulent virus to the defense mechanisms of the chicken. During the last five years, we have produced several virus construct candidates. Unfortunately, our modified viruses showed inconsistent protective effectiveness. Therefore, we returned to the drawing board and investigated whether extending our protein would improve protection. Using recombinant protein technology we showed that by using a larger portion of the viral attachment protein, binding to relevant chicken tissues was greatly improved. Furthermore, our results indicated that chickens injected with this extended recombinant protein vaccine were effectively protected against challenge. These results have led us to pursue two different strategies for vaccination. First, because vaccination by injection with a recombinant protein is neither cost-effective nor efficient in enormous broiler populations, we are currently evaluating vaccination with the recombinant protein using nanoparticles for in ovo delivery – injection into the egg. Second, based on the knowledge that the extended virus protein does confer effective protection against challenge, we are introducing genes producing this protein into a harmless virus (a virus routinely used worldwide for vaccination against Newcastle disease), and determining if this route of vaccine delivery is feasible and effective for chicken flocks.

Affordable poultry protein has significantly benefited the human population during the last decades. Mass food-animal production, to satisfy the increasing demand of protein, has provided an opportunity for viruses and other pathogens to become highly prevalent in these densely-maintained animal populations. Treatment of diseases once they have occurred in food animals is not only laborious and costly, but in addition, it may add undesirable products to the human food chain. Therefore, preventing diseases with novel vaccines seems the most effective method to secure this essential human food supply.