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Classical swine fever (CSF) has been controlled following extensive vaccination with the lapinized attenuated vaccine C-strain for decades in China. However, frequent CSF outbreaks occurred recently in a large number of C-strain-vaccinated pig farms in China and a new subgenotype 2.1d of CSFV has been reported to be responsible for the outbreaks.
The results showed that the C-strain adapted to the continuous ST cell line (CST) contain a unique M290K variation on the E2 protein, compared to those of primary BT cells (CBT) or rabbit origin (CRT) and the traditional C-strain sequences available in the GenBank database. Serum neutralization test revealed the antigenic differences between CST and CBT or CRT. Notably, the neutralizing titers of porcine anti-C-strain sera against the CSFV isolate of subgenotype 2.1d were significantly lower than those against C-strain or Shimen strain. The C-strain-vaccinated, subgenotype 2.1d HLJZZ2014 strain-challenged pigs did not show any clinical signs and all survived. However, these pigs displayed mild pathological and histological lesions, and the CSFV viral RNA was detected in the various tissue and blood samples.
Taken together, the C-strain-based vaccines of different origins showed molecular variations and antigenic differences, and could provide clinical but not pathological and virological protection against the subgenotype 2.1d CSFV emerging in China. Further investigation is needed to comprehensively assess the efficacy of C-strain of different doses against the subgenotype 2.1d CSFV.
Yuzi Luo, Shengwei Ji, Jian-Lin Lei, Guang-Tao Xiang, Yan Liu, Yao Gao, Xing-Yu Meng, Guanglai Zheng, En-Yu Zhang, Yimin Wang, Ming-Liang Du, Yongfeng Li, Su Li, Xi-Jun He, Yuan Sun. Efficacy evaluation of the C-strain-based vaccines against the subgenotype 2.1d classical swine fever virus emerging in China. Veterinary Microbiology. Volume 201, March 2017, Pages 154–161. https://doi.org/10.1016/j.vetmic.2017.01.012