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Abstract
AIM: To determine the efficacy of conjunctival vaccination of captive brushtail possums (Trichosurus vulpecula) with bacille Calmette-Guérin (BCG), as measured by immunological responses to vaccination and response to intratracheal challenge with Mycobacterium bovis.
METHODS: Nine adult male brushtail possums were vaccinated by the instillation of a suspension of BCG strain Pasteur 1173P2 into the conjunctival sac of each eye. Each drop contained approximately 2.5 × 105 colony forming units (cfu). At 8 weeks post-vaccination (pv) the vaccinated possums and 10 unvaccinated possums were challenged by intratracheal instillation of approximately 100 cfu of M. bovis. Cellular immune responses to bovine purified protein derivative (PPD) antigen were measured using the lymphocyte proliferation assay (LPA). Possums surviving to 50–51 days after challenge were euth anised and subjected to detailed post-mortem examination, including histopathology, to assess protection against tuberculosis. Sections of lung and spleen were cultured for M. bovis.
RESULTS: No conjunctival inflammation or other adverse reactions to the administration of the vaccine were evident macroscopically. The vaccinated group showed a systemic cellular immune response to bovine PPD antigen at 4 and 8 weeks pv, and the response at 8 weeks was significantly greater than at 4 weeks (p<0.05). Conjunctival vaccination induced significant levels of protective immunity, measured as less mass of tuberculous lesions in lung (p<0.05) and less dissemination of disease in vaccinated compared with unvaccinated possums (p<0.05).
CONCLUSIONS: Conjunctival vaccination with BCG induced a significant level of protective immunity against M. bovis infection in possums. This route of vaccination, together with intranasal aerosol vaccination, could be utilised in the delivery of an aerosolised vaccine using a device that sprays the vaccine suspension into the eyes and nose of possums.
Acknowledgements
This project was funded by the Animal Health Board. The authors would like to thank Professor Roger Morris and Dr Geoff de Lisle for helpful advice. The conscientious technical support of Mrs Donna Goile, the late Mr Ron Goile, Mrs Denise Keen, Mrs Natalie Parlane, Mr Gary Yates, Mrs Pat Davey and Mrs Pam Slack was greatly appreciated.