Oral immunisation against classical swine fever (CSF): onset and duration of immunity.

In an experimental study, onset and duration of immunity after oral immunisation of pigs with a classical swine fever (CSF) live virus vaccine based on the strain "C" has been evaluated. Sixteen weaner piglets (group 1) were orally instilled by syringe with the content of one vaccine bait whereas eighteen piglets (group 2) were fed with one bait. Six unvaccinated piglets represented the control group (group 3). The pigs having 2, 4, 6 and 10 days post vaccination (p.v.) were challenged with the highly virulent CSF virus (CSFV) strain "Koslov" to detect onset of immunity. After oral instillation of vaccine (group 1) the pigs were protected from a clinical infection 4 days p.v. One of four piglets reacted for a short time with an increase of body temperature. In group 2, a partial protection was already detected on day 2 p.v. On day 10 p.v., all animals were resistant to an experimental challenge infection. No protective neutralising antibodies were elicited until day 10 p.v. in both groups. Three animals of each group vaccinated orally against CSF were challenged approximately 6 and 10 months p.v. to evaluate duration of immunity. All vaccinated pigs developed neutralising antibodies and showed a protective immunity against an infection with CSFV until 10 months p.v. Furthermore, no vaccinated animal developed a viraemia after challenge. Altogether, 5 of 34 vaccinated pigs as well as all controls died after infection and showed typical gross lesions for CSF. The tonsils of the surviving pigs were negative for viral antigen by immunofluorescence.