Determination of the onset of the herd-immunity induced by the E2 sub-unit vaccine against classical swine fever virus.

摘要

For a recently developed E2 subunit vaccine against classical swine fever (CSF), the reduction in transmission, at different moments after vaccination, was assessed by animal experiments and statistical calculations. Two experiments were performed to estimate the reproduction ratio R. Experiment 1 consisted of 3 groups and experiment 2 of 2 groups, each of 10 pigs. In 4 of these groups, all pigs were vaccinated intramuscularly with the vaccine. The pigs in the 5th group remained unvaccinated (control group). After treatment, half of each group was intranasally inoculated with the virulent CSF virus strain Brescia. In the vaccine groups, the following vaccination-challenge intervals were applied: 14, 14, 10 and 7 days, respectively. The occurrenceof contact-infection was determined using the Erns ELISA. In the 7-days interval group and in the control group, virus transmission to all contact pigs occurred, indicating R>1. Neither in the two 2-week interval groups nor in the 10-day interval group did contact-infections occur. Hence, the estimated R is <1, which indicates that an epidemic would fade out. It is suggested that the E2 subunit vaccine may be an efficacious tool in a control programme during an outbreak of CSF as from 10 days after vaccination.