Date of Completion

9-9-2016

Embargo Period

9-7-2016

Keywords

vaccine, marker, DIVA, CSFV, attenuation, virulence

Major Advisor

Guillermo Risatti

Associate Advisor

Manuiel Borca

Associate Advisor

Paulo Verardi

Associate Advisor

none

Associate Advisor

none

Field of Study

Pathobiology

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Classical Swine Fever Virus (CSFV) is an extremely contagious, hemorrhagic and often fatal disease of pigs that causes serious socioeconomic impact on countries which experience outbreaks or are endemically infected. Current control measures utilized for CSFV are contingent upon the epidemiological status of the inflicted area and entail either prophylactic vaccination or non-vaccination, “stamping out”, protocol with the elimination of infected herds and culling of animals on neighboring farms. This latter practice results in less than satisfactory consequences, although once thought to be the answer to eradication of CSFV from a region, “stamping out” results in tremendous economic losses as well as the ethical objection to the potential killing of millions of healthy pigs. Marker vaccines also referred to as DIVA vaccines because they allow for differentiation between naturally infected and vaccinated animals (DIVA), could complement or replace the “stamping out” strategy. The use of a DIVA vaccine with an accompanying diagnostic test would make mass vaccination of susceptible pigs during and outbreak possible thereby preventing the rapid spread of the virus while allowing for identification of CSFV infected animal through serological surveillance. With the advent of reverse genetic technology, it is now possible to rationally design a CSFV vaccine that contains such markers. Recently, we reported the development of a live attenuated CSFV strain with two antigenic markers, named Flag T4v. During the vaccine assessment process, Flag T4v showed evidence of reverting back to the virulent phenotype of wild type CSFV. Analysis of the genome sequence from the recovered revertant virus revealed the presence of four non synonymous substitutions and a deletion of one of the antigenic epitopes compared to the parental Flag T4v genome. In order to improve the genetic stability of Flag T4v, the nucleotide codon sequence in these regions was modified as much as possible from its original sequence without compromising the wild type amino acid sequence by taking advantage of codon redundancy in an attempt to make viral reversion more difficult while maintaining both viral attenuation and reactivity of the antigenic markers. The newly developed virus, Flag T4Gv, was shown to be stably attenuated when assessed in a reversion to virulence test. In addition, Flag T4Gv was also shown to possess similar efficacy of Flag T4v in terms of protecting swine at early and late times post vaccination.

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