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Study on the local effect of eye-drop vaccination against infectious bronchitis in 1-day-old chicks with maternal
1Department of Poultry Diseases, State University Utrecht, Doorn, The Netherlands.
Insights
Eye-drop vaccination against infectious bronchitis virus (IBV) protects chicks locally in the eyes and nose. However, chicks remain susceptible to IBV when challenged intratracheally, highlighting the importance of challenge route in vaccine studies.
Area of Science:
- Veterinary Virology
- Immunology
Background:
- Maternal antibodies can interfere with vaccination efficacy in poultry.
- Infectious Bronchitis Virus (IBV) is a significant respiratory pathogen in chickens.
Purpose of the Study:
- To evaluate the protective efficacy of an eye-drop administered IBV vaccine in chicks with maternal antibodies.
- To determine the influence of challenge route on vaccine effectiveness against IBV.
Main Methods:
- One-day-old chicks with maternal IBV antibodies were vaccinated via eye-drop with the H120 vaccine strain.
- Four weeks post-vaccination, chicks were challenged with a virulent IBV Massachusetts-type field strain via eye-drop or intratracheally.
- Clinical signs, immunofluorescence, gross and microscopic lesions, and serum neutralization index were assessed.
Main Results:
- Chicks demonstrated resistance to ocular challenge but susceptibility to intratracheal challenge.
- Intratracheal challenge resulted in clinical signs of infectious bronchitis and tracheal lesions.
- Serum neutralization index was higher in intratracheally-challenged birds compared to eye-drop challenged or unchallenged birds.
Conclusions:
- Eye-drop vaccination against IBV primarily induces localized protection in conjunctival and nasal tissues.
- The route of challenge virus application significantly impacts the assessment of vaccine efficacy in IBV studies.
- Maternal antibodies may not fully inhibit the local immune response induced by eye-drop vaccination.
Abstract:
One-day-old chicks with maternal antibodies to infectious bronchitis virus (IBV) were vaccinated by eye-drop with H120 vaccine strain of IBV. Four weeks later the chicks were challenged by eye-drop or intratracheally with virulent IBV (Massachusetts-type field strain). The chicks were resistant to ocular challenge, but highly susceptible to an intratracheal challenge. After intratracheal challenge the birds showed clinical signs of infectious bronchitis (IB). The immunofluorescence test on IBV was positive. Macroscopical and microscopical lesions were present in the trachea. From these observations it was concluded that the protection against virulent IBV after eye-drop vaccination is localised mainly in the conjunctival and nasal tissues. Thus in vaccination studies with IBV the result of challenge depended highly on the route of application of the challenge virus. Ten days after challenge the neutralisation index of serum for IBV was significantly higher in the intratracheally-challenged chicks as compared with their eye-drop challenged or/and unchallenged mates.
