Evaluation of protective efficacy when combining HVT vector vaccines

Authors: Dunn, John; DIMITROV, KIRIL - Consultant; MILLER, PATTI - University Of Georgia; GARCIA, MARICARMEN - University Of Georgia; TURNER-ALSTON, KELLY - Zoetis; BROWN, AMY - Zoetis; HARTMAN, ANGELA - Zoetis

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2018
Publication Date: 12/17/2018
Citation: Dunn, J.R., Dimitrov, K.M., Miller, P.J., Garcia, M., Turner-Alston, K., Brown, A., Hartman, A. 2018. Evaluation of protective efficacy when combining HVT vector vaccines. Avian Diseases. 63(1):75-83. https://doi.org/10.1637/11979-092818-Reg.1.
DOI: https://doi.org/10.1637/11979-092818-Reg.1

Interpretive Summary: Turkey herpesvirus (HVT) is widely used as a vaccine against Marek’s disease in chickens and recently has been used as a vaccine that carries a portion of other poultry viruses, allowing protection against multiple poultry diseases. This type of vaccine that protects against multiple diseases has grown in popularity due to safety and other unique features. As new products have come out, producers discovered that mixing together multiple vaccines of this type caused interference with each other. We confirmed this interference by combining products and evaluating protection against Newcastle disease (ND), infectious laryngotracheitis (ILT), and infectious bursal disease (IBD). We found that the ILT product was most severely affected by the addition of other vaccines. This study demonstrates the importance for following manufacturer guidelines and the need for validating alternative strategies to benefit from the high level of protection offered by vector vaccines.

Technical Abstract: Turkey herpesvirus (HVT) is widely used as a vaccine against Marek’s disease in chickens and recently as a vector for foreign genes from infectious bursal disease virus, Newcastle disease virus, infectious laryngotracheitis virus, and avian influenza virus. Advantages of HVT-vector vaccines are that the vaccines do not contain live respiratory viruses able to replicate and cause disease or embryo mortality, they can be administered at hatch or in ovo, and are relatively insensitive to interference from maternally derived antibodies. As producers have tried to combine HVT vector vaccines to protect against additional diseases, reports have indicated that applying two vectored vaccines using the same HVT vector is reported to reduce the efficacy of one or both vaccines. To confirm this interference, we evaluated commercial vaccines from multiple companies, including products with inserts designed to protect against Newcastle disease (ND), infectious laryngotracheitis (ILT), and infectious bursal disease (IBD). We found that the ILT product was most severely affected by the addition of other vaccines, as demonstrated by significant increase in clinical signs, significant decrease in weight gain, and increase in quantity of challenge virus observed from tracheal swabs collected from days 3-5 post-challenge. The ND and IBD products were also affected by addition of other vaccines, although in most cases differences compared to vaccination with the vector alone were not statistically significant. This study demonstrates the importance for following manufacturer guidelines and the need for validating alternative strategies to benefit from the high level of protection offered by vector vaccines.