In the paper are presented the results of investigating protective effect of attenuated live vaccine against classical swine fever (CSF) under experimental conditions. The vaccine contains C-strain of CSF. In the Republic of Serbia it is used for systemic immunoprophylaxis. Potency testing was performed according to the guidelines of the European Pharmacopoeia, 5th Edition, 2005 (01/2005:0065) and the guidelines published by the World Organisation for Animal Health (OIE) (Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, 5th Edition, 2008, Vol. 1, Chapter 2.8.3). The experiments were carried out on twelve weaner pigs seven weeks of age randomly assigned to two groups consisting of five, and one group consisting of two pigs. Before introducing the experimental protocol of vaccination and artificial infection, the presence of specific antibodies against CSF was controlled by ELISA test, i.e. by serum neutralisation test that proved no presence of antibodies against bovine virus diarrhea (BVD). The pigs in the fist group were vaccinated with attenuated live vaccine Lavir-K® (Veterinary Institute Zemun a.d. Belgrade) in a 1:40 dilution, and the pigs from second group were vaccinated in a 1:160 dilution. The group three served as a control group that was not vaccinated. Fourteen days post vaccination all animals were challenged with highly virulent CSF virus strain Beker, and fourteen days after artificial infection animals were daily observed and their body temperature was recorded. In the group of animals vaccinated with vaccine Lavir-K® in a 1:40 dilution there were no clinical characteristic symptoms of CSF, while in the group vaccinated in a 1:160 dilution two pigs became ill with obvious CSF symptoms. One pig died on day 7 p.v. In the control group, i.e. two non-vaccinated pigs, there was an acute form of CSF and they died seven days after the infection. Calculation of the Protective Dose 50 (PD50) of Lavir-K® was done using the equation by Spearman-Kaerber and it was calculated to be 184. Having in mind that one vaccine doses should have protective value of > 100, it may be concluded that tested vaccine fulfils the requirements for vaccine potency as laid down in the European Pharmacopoeia and the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals.
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