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

In an experimental study, onset and duration of immunity after oral immunis ation of pigs with a classical swine fever (CSF) live virus vaccine based o n the strain "C" has been evaluated. Sixteen weaner piglets (group 1) were orally instilled by syringe with the content of one vaccine bait whereas ei ghteen piglets (group 2) were fed with one bait. Six:unvaccinated piglets r epresented 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 instillati on of vaccine (group I) the pigs were protected from a, clinical infection 4 days p.v. One of four piglets reacted for a short time with an increase o f body temperature. In group 2, a partial protection was already detected o n day 2 p.v. On day 10 p.v., all animals were resistant to an experimental challenge infection. No protective neutralising antibodies were elicited un til day 10 p.v. in both groups. Three animals of each group vaccinated oral ly against CSF were challenged approximately 6 and 10 months p.v. to evalua te duration of immunity. All vaccinated pigs developed neutralising antibod ies and showed a protective immunity against an infection with CSFV until 1 0 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 infe ction and showed typical gross lesions for CSF. The tonsils of the survivin g pigs were negative for viral antigen by immunofluorescence. (C) 2001 Else vier Science B.V. All rights reserved.