| Summary: | 碩士 === 國立中興大學 === 獸醫病理生物學研究所 === 102 === Classical swine fever (CSF) is a highly contagious and lethal disease of swine. There has been no case of acute CSFV infection reported to OIE since 2006 from Taiwan, which could be a good opportunity for promoting CSF eradication. Thus, the first part of this study was to survey the prevalence of CSF virus (CSFV) infection in Taiwan by using RT-nPCR. Results showed that 17.2% of necropsy samples (N=93) and 14.4% of tonsil swabs and saliva of ill nursery pigs were positive for CSFV nuclear acid, but those positive specimens submitted for viral isolation were all negative. Furthermore, the results of monitoring CSFV nuclear acid in sows’ saliva showed no evidence of CSFV positives on 3 target farms before using E2 subunit vaccine, however, 13.3% and 40% of samples from 2 target farms, respectively, turned to positive for CSFV nuclear acid after using E2 subunit vaccine for 11 months. The results of viral isolation of those 2 target farms remained negative, and no clinical infection occurred. Secondly, in order to reduce the vaccination stress on nursery pigs, a retrospective analysis of CSFV antibody responses after applying to different vaccination programs was undertaken. The results showed that the seropositive rates of pigs with double vaccinations at 3&6 and 6&9 were better than pigs receiving single vaccination on 6 weeks of age, but there was no statistic significantly difference among these 3 vaccination programs (p>0.05). The final part of this study was to monitor CSFV antibody response after using the new developed E2 subunit vaccine. The results indicated that sows firstly boosted with E2 subunit vaccine could provide high maternal antibody to the piglets and last for 11-12 weeks. Besides, monitoring on a CSFV endemic farm (Farm SY) after massive vaccination with CSFV E2 subunit vaccine on sows and PCV2 vaccine on 3 weeks old piglets showed that the positive detection of CSF viral nuclear acid in saliva of nursery pigs was dramatically decreased from 25% to 0%. In conclusion, chronic and subclinical CSF is still existed in a few pig farms. In addition, single vaccination at 6-week-old piglets followed by elevating biosecurity levels and good management is required for CSF eradication and could reduce the stresses caused by secondary booster at 8-9 weeks of age. Furthermore, if sows are consistently boosted with E2 subunit vaccine, it could provide high and prolonged protection to piglets and the CSF vaccination can be delayed to pre-finisher stage that may be beneficial for CSFV elimination in endemic farms.
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