Oral immunisation of swine with a classical swine fever vaccine (Chinese strain) and transmission studies in rabbits and sheep

Seven experiments including a total of 47 pigs, 11 wild boars, 26 rabbits, 10 hares and 16 sheep were carried out to assess the efficacy, safety and t ransmission of the Chinese vaccine strain of the classical swine fever viru s (CSFV) administrated by the oral route. Within 3 weeks after oral vaccina tion, a clear seroconversion occurred in the pigs. Six weeks after vaccinat ion, vaccinated pigs were fully protected against a virulent challenge. The C-strain was not isolated from tonsils, spleen, lymph nodes, thymus, saliv a, urine and faeces of pigs within 4 days after oral vaccination. In one ex periment, susceptible pigs were placed in direct contact with vaccinated pi gs, None of these contact-exposed pigs became serologically positive for CS FV antibodies. It is concluded that the C-strain induces protection in pigs when administrated by the oral route and is not shed by vaccinated pigs. S erum anti-CSFV antibodies developed in seven out of eight wild boars vaccin ated by the oral route. No vaccine virus was detected in the spleen and ton sils of these animals. The results in wild boar were in accordance with tho se obtained in domestic pigs. Sheep did not show any clinical signs after o ral vaccination while rabbits had moderate hyperthermia and growth retardat ion. No clinical response to oral immunisation in hares was detected. At th e end of the experiment, no sheep had detectable serum antibodies against C SFV, whereas a few vaccinated rabbits and hares became seropositive. None o f the contact-exposed rabbits and hares seroconverted. These data indicate that the C-strain is safe for sheep and as expected, moderately or not path ogenic for rabbits and hares. These efficacy and safety studies on oral vac cination with the C-strain under experimental conditions provide essential information for further studies in wild boars under experimental and field conditions, including assays with baits to control a CSF epidemic. (C) 1999 Elsevier Science B.V. All rights reserved.