Adverse Effects of Classical Swine Fever Virus LOM Vaccine and Jeju LOM Strains in Pregnant Sows and Specific Pathogen-Free Pigs

Abstract

In Jeju island of South Korea, a classical swine fever (CSF) non-vaccinated region, many pig farmers insisted on abortion and stillbirth in pregnant sows and high mortality of suckling/weaning piglets by circulating CSF virus from 2014 to 2018. We investigated whether CSF viruses isolated from pigs in Jeju Island (Jeju LOM) have recovered their pathogenicity by conducting experiments using pregnant sows and specific pathogen-free (SPF) pigs. The CSF modified live LOM vaccine (MLV-LOM) and Jeju LOM strains induced abortion and stillbirth in pregnant sows. Viral antigens were detected in the organs of fetuses and stillborn piglets in the absence of specific pathological lesions associated with the virulent CSF virus in both groups (MLV-LOM and Jeju LOM strain). However, antigen was detected in one newborn piglet from a sow inoculated with a Jeju LOM strain, suggesting that it may cause persistent infections in pigs. SPF pigs inoculated with the MLV-LOM or Jeju LOM strains were asymptomatic, but virus antigen was detected in several organ and blood samples. Virus shedding in both groups of animals was not detected in the feces or saliva until 21 days post inoculation. The serum concentration of the three major cytokines, IFN-α, TNF-α, and IL-10, known to be related to lymphocytopenia, were similar in both groups when the MLV-LOM or Jeju LOM strains were inoculated into SPF pigs. In conclusion, Jeju LOM strains exhibited most of the characteristics of the MLV-LOM in pigs and resulted in the same adverse effects as the MLV-LOM strain.

Serodynamic Analysis of the Piglets Born from Sows Vaccinated with Modified Live Vaccine or E2 Subunit Vaccine for Classical Swine Fever

“…The CSFV MLV vaccine can induce not only humoral immune responses but also cell-mediated immune responses against virulent CSFV [ 14 ]. However, several disadvantages of CSFV MLV vaccines have been identified: i) a lack of DIVA according to serological assays [ 16 , 20 ]; ii) the adverse effects of the CSFV MLV vaccine in vaccinated pigs [ 32 , 33 ]; iii) pig-to-pig transmission of MLV [ 32 ]; and iv) farm-to-farm transmission of MLV by vehicles [ 32 ]. Additionally, the influence of MDA on the efficacy of CSFV MLV in the field has been well discussed [ 14 , 15 , 16 , 17 , 18 , 19 ].…”

Evaluation of classical swine fever E2 (CSF-E2) subunit vaccine efficacy in the prevention of virus transmission and its potential application for virus eradication in field farms

“…In 2015, Japan was o cially announced by OIE to be CSF-free and added to the list of countries with CSF-free status after conducting a successful 10-year eradication program; however, several sporadic reemerging incursions transmitted from wild boar to the domestic population have been reported recently [39][40][41]. In addition, CSF reemerged accidentally in the Jeju island of South Korea after the unintentional vaccination of live attenuated CSF vaccine (LOM strain) on naïve pigs in 2014 [42][43][44]. The alignment sequences of eld virulent CSFV strains in the Jeju island (Jeju LOM strain) and the LOM vaccine strain had a high identity on the amino acid sequence (98.7-99.0%) [44].…”

“…The alignment sequences of eld virulent CSFV strains in the Jeju island (Jeju LOM strain) and the LOM vaccine strain had a high identity on the amino acid sequence (98.7-99.0%) [44]. Inoculation trials in SPF pigs and pregnant sows indicate that the CSFV Jeju LOM strain had the most characteristics of the LOM vaccine strains and may cause persistent infection in fetuses [42]. Hence, the safety of live attenuated CSF vaccines should be considered more in eld farm applications.…”

Protection of Piglets with Maternally Derived Antibodies from Sows Inoculated with an Attenuated Live Marker Classical Swine Fever Vaccine (Flc-LOM-BErns)

“…NS-CSF-31, Cheonchen, South Korea), which employs TaqMan probes, detects the CSFV 5'UTR with high specificity, but it does not detect BVDV or border disease virus, which also belongs to the genus Pestivirus. The assay was performed as described previously [25].…”