Submitted to: Avian Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2017
Publication Date: 12/20/2017
Citation: Spackman, E., Stephens, C., Pantin Jackwood, M.J. 2017. The effect of infectious bursal disease virus induced immunosuppression on vaccination against highly pathogenic avian influenza virus. Avian Pathology. 62(1):36-44. https://doi.org/10.1637/11769-110717-Reg.1.
Interpretive Summary: Vaccination is used to control bird flu in many parts of the world. Success can be variable and depends on numerous factors. One factor that may contribute to situations where vaccines don't provide the level of protection that is expected is viruses that impair the immune system. Among poultry species there are several viruses that decrease immunity and lead to increases in other diseases. A virus called "infectious bursal disease virus" or IBDV, is very common in chickens and is very difficult to kill. If chickens are infected at a very young age with IBDV their immune system may never be fully functional. It was the aim of this work to see if impairment of the immune system by IBDV would affect infection with bird flu with and without vaccination. The result was that IBDV essentially eliminated the effect of the bird flu vaccine. This adds a piece to the puzzle of understanding why bird flu vaccines can fail to protect chickens.
Technical Abstract: Poor efficacy of avian influenza virus (AIV) vaccines in chickens has been documented in the field in spite of good results in experimental settings. Although the causes are multifactorial and complex, one contributing factor may be prior infection with immunosuppressive viruses. In an effort to evaluate the role of immunosuppressive agents on AIV pathogenesis and vaccine efficacy, the effect of prior infection with infectious bursal disease virus (IBDV), a ubiquitous immunosuppressive virus of chickens, was evaluated. Specific-pathogen-free white Plymouth Rock chickens were exposed to variant E IBDV at 1 day of age and were subsequently vaccinated with an inactivated H7 AIV vaccine 2 wk later. Vaccinated chickens exposed to IBDV had a geometric mean antibody titer to AIV of 1:1.7 by hemagglutination inhibition assay compared to a geometric mean titer of 1:47.5 from chickens that were vaccinated but not exposed to IBDV. Three weeks postvaccination, the chickens were challenged with one of six different doses of highly pathogenic (HP) AIV homologous to the vaccine. Within challenge virus dose groups, vaccinated chickens exposed to IBDV had similar mortality rates to nonvaccinated chickens that were not exposed to IBDV. In contrast, vaccinated chickens that were not exposed to IBDV were protected from mortality. Exposure to IBDV also decreased the mean death time (2.3–3.7 days depending on dose) compared with vaccinated birds not exposed to IBDV (4– 7 days depending on dose). Neither vaccination nor IBDV infection had an effect on mean bird infection dose with HPAIV, but the 50% bird lethal dose was reduced from .106 50%egg infective dose (EID50) in the vaccinated, IBDV-nonexposed group to 103.3 EID50 in the vaccinated group exposed to IBDV. These results are consistent with IBDV exposure contributing to poor vaccine efficacy in the field.