Transmissibility of Infectious Bronchitis Virus H120 Vaccine Strain Among Broilers under Experimental Conditions

M.G.R. Matthijs, A. Bouma, F.C. Velkers, J.H.H. van Eck, J.A. Stegeman

    Research output: Contribution to journalArticleAcademicpeer-review


    The aim of this study was to quantify transmission of infectious bronchitis virus (IBV) H120 vaccine strain among
    broilers, and to assess whether birds that have been exposed to vaccine strain-shedding birds were protected against clinical signs
    after infection with a virulent strain of the same serotype. A transmission experiment and a replicate were carried out, each with six
    groups of commercial broilers. At day of hatch (n 5 30) or at 15 days of age (n 5 20), half of each group was inoculated with either
    IBV H120 vaccine (H120 group), virulent IBV M41 (M41 group), or were mock-infected, thereby contact-exposing the other half
    of each group. Nasal discharge was recorded, and antibody response and virus shedding were measured. To measure clinical
    protection, four weeks after inoculation all birds, in all groups, were challenged with IBV M41. The reproduction ratio (R; the
    average number of contact infections caused by one infectious bird) was determined to quantify virus transmission. All contactexposed
    birds, except for one in an H120 group, became infected with either IBV H120 or IBV M41. Almost all birds contactinfected
    with IBV H120 or IBV M41 were subsequently protected against clinical signs after challenge with IBV M41. The lower
    limits of the 95% confidence interval (CI) of the R of IBV H120 vaccine, and of IBV M41, were significantly ,1. For both IBV
    H120 and IBV M41, the 95% CI was [2.1–‘] following inoculation at day of hatch and [1.8–‘] after inoculation at 15 days of
    age. This finding demonstrates that IBV H120 vaccine is able to spread extensively among broilers. This implies that this vaccine
    strain might be able to become endemically present in the poultry population. It also implies that, even if not all birds received
    vaccine during spray application, due to the ability of the vaccine to spread in the flock, they will most likely be protected against
    clinical signs after a subsequent field virus infection.
    Original languageEnglish
    Pages (from-to)461-466
    Number of pages6
    JournalAvian Diseases
    Issue number3
    Publication statusPublished - 2008


    • infectious bronchitis virus
    • transmission
    • vaccine
    • broilers


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