Foot-and-mouth disease (FMD) is one of the most contagious diseases affecting economically important livestock species and remains the single biggest emergency animal disease threat to the Australian red meat, dairy, wool and pig industries. Potential costs to Australia due to an outbreak of FMD have been estimated at $50B over 10 years, of which less than 1% will be related to the actual costs of controlling the disease (ABARES Report, 2013). Control plans would consider vaccination of cattle as one of the measures if there is an incursion of FMD in Australia. However, a limited number of vaccine strains are available in the Australian vaccine bank and it is important to ensure those vaccines will be efficacious against contemporary field strains circulating in regions that are seen as threat for possible introduction.
Groups of cattle calves were vaccinated with O1 Manisa 69 high-potency vaccine (>6 PD50). All the vaccinated cattle, along with unvaccinated controls, were challenged by intradermolingual inoculation with a virulent virus belonging to a different genetic lineage on 4, 7 and 21 days post vaccination (dpv). The animals were observed for 8 days for the development of clinical signs and samples collected up to 14 or 35 days post challenge.
All cattle calves challenged on 21 dpv and half of those challenged on 7 dpv were protected against clinical disease. None of the animals that were challenged on 4 dpv or the unvaccinated controls were protected. Although vaccination prevented clinical disease as early as 7 dpv, it did not prevent subclinical virus infection. The antibody response to the structural and non-structural proteins of FMD virus, and virus excretion in oral and nasal secretions as well as the development of the ‘carrier state’ will be discussed.