Duration of the protection of an E2 subunit marker vaccine against classical swine fever after a single vaccination

The period during which pigs are protected after vaccination is important f or the successful usage of a marker vaccine against classical swine fever v irus (CSFV) in an eradication programme. In four animal experiments with di fferent vaccination-challenge intervals we determined the duration of prote ction of an E2 subunit marker vaccine in pigs after a single vaccination. U nvaccinated pigs were included in each group to detect transmission of the challenge virus. Three groups of six pigs were vaccinated once and subsequently inoculated w ith the virulent CSFV strain Brescia after a vaccination-challenge interval of 3, 51/2, 6 or 13 months. All vaccinated pigs, 16 out of 18, with neutra lising antibodies against CSFV at the moment of challenge, 3, 51/2, 6 or 13 months later, survived, whereas unvaccinated control pigs died from acute CSF or were killed being moribund. A proportion of the vaccinated pigs did however develop fever or cytopenia after challenge and two vaccinated pigs were viremic after challenge. Virus transmission of vaccinated and challeng ed pigs to unvaccinated sentinel pigs did not occur in groups of pigs which were challenged 3 or 6 months after a single vaccination. Two out of eight vaccinated pigs that were found negative for CSFV neutralising antibody at 13 months after vaccination died after subsequent challenge. The findings in this study demonstrate that pigs can be protected against a lethal challenge of CSFV for up to 13 months after a single vaccination wi th an E2 subunit marker vaccine. (C) 2001 Elsevier Science B.V. All rights reserved.