Abstract
Classical swine fever (CSF) caused by the CSF virus (CSFV) is one of the most important swine diseases, resulting in huge economic losses to the pig industry worldwide. Systematic vaccination is one of the most effective strategies for the prevention and control of this disease. Two main CSFV vaccines, the modified live vaccine (MLV) and the subunit E2 vaccine, are recommended. In Taiwan, CSF cases have not been reported since 2006, although systemic vaccination has been practiced for 70 years. Here, we examined the sero-dynamics of the piglets born from sows that received either the CSFV MLV or the E2 vaccine and investigated in the field the correlation between the porcine reproductive and respiratory syndrome virus (PRRSV) loads and levels of CSFV antibody. A total of 1398 serum samples from 42 PRRSV-positive farms were evaluated to determine the PRRSV loads by real-time PCR and to detect CSFV antibody levels by commercial ELISA. Upon comparing the two sow vaccination protocols (CSFV MLV vaccination at 4 weeks post-farrowing versus E2 vaccination at 4–5 weeks pre-farrowing), the lowest levels of CSFV antibody were found in piglets at 5–8 and 9–12 weeks of age for the MLV and E2 groups, respectively. Meanwhile, the appropriate time window for CSFV vaccination of offspring was at 5–8 and 9–12 weeks of age in the MLV and E2 groups, respectively. There was a very highly significant negative correlation between the PRRSV load and the level of CSFV antibody in the CSFV MLV vaccination group (P < 0.0001). The PRRSV detection rate in the pigs from the MLV group (27.78%) was significantly higher than that in pigs from the E2 group (21.32%) (P = 0.011). In addition, there was a significant difference (P = 0.019) in the PRRSV detection rate at 5–8 weeks of age between the MLV (42.15%) and E2 groups (29.79%). Our findings indicate that the vaccination of CSFV MLV in piglets during the PRRSV susceptibility period at 5–8 weeks of age may be overloading the piglet’s immune system and should be a critical concern for industrial pork production in the field.
Highlights
Classical swine fever (CSF) caused by the CSF virus (CSFV) is one of the most important swine diseases, resulting in huge economic losses to the pig industry worldwide, and it is a World Organization for Animal Health (OIE)-listed disease
Upon comparing the two sow vaccination protocols (CSFV modified live vaccine (MLV) vaccination at 4 weeks post-farrowing versus E2 vaccination at 4–5 weeks pre-farrowing), the lowest levels of CSFV antibody were found in piglets at 5–8 and 9–12 weeks of age for the MLV and E2 groups, respectively
Our findings indicate that the vaccination of CSFV MLV in piglets during the porcine reproductive and respiratory syndrome virus (PRRSV) susceptibility period at 5–8 weeks of age may be overloading the piglet’s immune system and should be a critical concern for industrial pork production in the field
Summary
Classical swine fever (CSF) caused by the CSF virus (CSFV) is one of the most important swine diseases, resulting in huge economic losses to the pig industry worldwide, and it is a World Organization for Animal Health (OIE)-listed disease. CSFV (previously called hog cholera virus) belongs to the genus Pestivirus within the family Flaviviridae together with bovine viral diarrhea virus 1, bovine viral diarrhea virus 2 and border disease virus [1]. CSFV has been redesignated as Pestivirus C [1]. CSF is an immunosuppressive disease in which several immune escape mechanisms of CSFV have been reported, such as apoptosis, autophagy and pyroptosis in bone marrow hematopoietic cells, lymphocytes and lymphoid organs [2]. A low CD4/CD8 ratio has been observed in the peripheral blood mononuclear cells of infected fetuses and piglets challenged with either high- or low-virulence CSFV strains. During CSFV infection, the clinical signs mainly depend on the ages of pigs and the virulence of the viral strains. The clinical forms of CSFV can show acute, chronic and persistent courses
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