Abstracts

Classical swine fever (CSF) is a highly contagious viral disease of domestic and wild pigs, included in the list of diseases notifiable to the World Organisation for Animal Health. The causative agent, CSF virus (CSFV), belongs to the Pestivirus genus, Flaviviridae family. Over the last century, great efforts have been directed towards the control and eradication of CSF, which today remains one of the most important diseases for animal health and in the pig industry worldwide. The circulation and intrinsic importance of low and moderate virulence strains in the endemic regions has been extensively described. Also, it has been shown the role of these type of viral strains in the generation of the pregnant carrier sow syndrome and persistent infection of piglets after trans-placental transmission. However, the mechanisms involved in this form of CSFV infections are not well known, and the existing studies date over 40 years ago. By contrast, the possible generation of viral persistence after postnatal infection of pigs is still a question to resolve.Against this background, this thesis has demonstrated the capacity of low and moderate virulence CSFV strains to produce postnatal persistent infection early after birth. To this end, newborn piglets were inoculated intranasally with CSFV. During six weeks, these piglets remained apparently healthy, although they were not able to generate detectable CSFV specific humoral nor cellular immune responses, maintaining high virus load in blood, organs and body secretions and excretions. In addition, it has been demonstrated the ineffectiveness of vaccination of six-week-old PI pigs, which were unable to elicit a detectable innate immune response, in terms of IFN type-I production, as well as acquired immune responses (i.e. IFN type-II and antibodies) following vaccination with a CSFV live attenuated vaccine (C-strain). The RNA of the vaccine could not be detected by a specific RT-qPCR in any of the samples analysed after vaccination, including the tonsil, suggesting a superinfection exclusion (SIE) phenomenon between the persistently infecting virus (primary infection) and the CSFV vaccine strain (secondary infection). Finally, six-week-old wild boars with CSFV persistent infection (first infection) were inoculated with a CSFV strain of high virulence (second infection or superinfection). PI wild boars did not develop clinical signs and showed a high load of the primary virus, causing persistence, in all samples analysed. In contrast, the secondary virus was not detected by either RT-qPCR or sequence analyses, thus demonstrating the phenomenon of superinfection exclusion (SIE). The lack of innate and acquired immune responses supported the previous studies from this thesis. In addition, in vitro assays with the PBMCs isolated ex vivo from persistently infected animals, a well-known target for the CSFV viral replication, further corroborated the CSFV SIE phenomenon. These findings demonstrated for the first time the ability of CSFV to induce SIE in vivo, in swine withAdvisors/Committee Members: [emailprotected] (authoremail), true (authoremailshow), Domingo lvarez, Mariano (director), true (authorsendemail).