Classical swine fever virus C-strain with eight mutation sites shows enhanced cell adaptation and protects pigs from lethal challenge
- 63 Downloads
Control of classical swine fever (CSF) in developing countries is achieved by immunization with attenuated vaccines, such as the lapinized C-strain vaccine that has been widely used in China. However, C-strain has relatively low growth rate in cell cultures, thus affecting productivity of the vaccine for the industry. In this study, eight amino acid residues were mutated on the C-strain backbone, resulting in a cell-adapted strain Cmut8. The mutant strain exhibited rapid growth with titer of about 100 fold higher than its parental C-strain. The mutation sites located at structural proteins Erns and E2 contributed more to cell adaptation than those located in non-structural proteins. Sera collected from pigs inoculated with Cmut8 and C-strain at the same dose showed similar antibody levels and neutralization titers. Pigs inoculated with different doses of Cmut8 (low, medium and high) and with C-strain offered full protection against challenge with a virulent strain, shown as absence of fever and other symptoms, marginal low levels of viral load, and no obvious gross pathological changes in major organs. Unvaccinated control pigs challenged with the virulent strain showed high fever from day 2 post-challenge and apparent clinical symptoms with two deaths. Viral load were markedly elevated in these control pigs after challenge. The pigs inoculated with high dose of Cmut8 did not show fever or other typical CSF symptoms, and no apparent pathological changes were observed in major organs. Besides, the Cmut8 strain did not induce typical fever response in rabbits. These results demonstrate that the cell-adapted Cmut8 strain remains non-pathogenic to the weaned pigs, provides full protection and could be a good candidate vaccine strain for improved yield at lower cost.
This study is part of the work sponsored by Zhejiang Provincial Department of Science & Technology (2019C02043), Shanghai Key Laboratory of Veterinary Biotechnology, Shanghai, China (KLAB201711) and Dabeinong Funds for Discipline Development and Talent Training in Zhejiang University (DB2018005).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Animal experiments were conducted following the guidelines and approved protocols of the Laboratory Animal Management Committee of Zhejiang University (Approval No. ZJU20180190 and 20181061).
- 5.Thiel HJ, Stark R, Weiland E, Rumenapf T, Meyers G (1991) Hog cholera virus: molecular composition of virions from a pestivirus. J Virol 65(9):4705–4712Google Scholar
- 6.Qiu HJ, Tong GZ, Shen RX (2005) The lapinized Chinese strain of classical swine fever virus: a retrospective review spanning half a century. J Integr Agric 38:1675–1685 (Chinese) Google Scholar
- 9.Graham SP, Everett HE, Haines FJ, Johns HL, Sosan OA, Salguero FJ, Clifford DJ, Steinbach F, Drew TW, Crooke HR (2012) Challenge of pigs with classical swine fever viruses after C-strain vaccination reveals remarkably rapid protection and insights into early immunity. PLoS One 7(1):e29310CrossRefGoogle Scholar
- 10.Moormann RJ, van Gennip HG, Miedema GK, Hulst MM, van Rijn PA (1996) Infectious RNA transcribed from an engineered full-length cDNA template of the genome of a pestivirus. J Virol 70(2):763–770Google Scholar
- 12.Tong C, Chen N, Liao X, Yuan X, Sun M, Li X, Fang W (2017) Continuous passaging of a recombinant C-strain virus in PK-15 cells selects culture-adapted variants that showed enhanced replication but failed to induce fever in rabbits. J Microbiol Biotechnol 27(9):1701–1710Google Scholar
- 13.Chen N, Tong C, Li D, Wan J, Yuan X, Li X, Peng J, Fang W (2010) Antigenic analysis of classical swine fever virus E2 glycoprotein using pig antibodies identifies residues contributing to antigenic variation of the vaccine C-strain and group 2 strains circulating in China. Virol J 7:378CrossRefGoogle Scholar
- 18.Chinese Ministry of Agriculture (2001) Quality Standards for Veterinary Biological Products of People’s Republic of China. Chinese Agricultural Science and Technology Press, Beijing, pp 84–85 (Chinese) Google Scholar
- 21.Dahle J, Liess B (1995) Assessment of safety and protective value of a cell culture modified strain “C” vaccine of hog cholera/classical swine fever virus. Berl Munch Tierarztl Wochenschr 108(1):20–25Google Scholar
- 22.Kaden V, Riebe B (2001) Classical swine fever (CSF): a historical review of research and vaccine production on the Isle of Riems. Berl Munch Tierarztl Wochenschr 114(7–8):246–251Google Scholar