Document Type

Dissertation - Open Access

Award Date

2019

Degree Name

Doctor of Philosophy (PhD)

Department / School

Veterinary and Biomedical Sciences

First Advisor

Diego G. Diel

Keywords

3C protease, Apoptosis, Pathogenesis, Seneca Valley Virus, Senecavirus A, Vesicular disease

Abstract

Senecavirus A (SVA) is a positive sense single-strand RNA virus of the genus Senecavirus, family Picornaviridae. Senecavirus A is an emerging picornavirus of swine, which causes vesicular disease (VD) in pigs that is clinically indistinguishable from footand- mouth disease and other high consequence VDs of swine. There is evidence that SVA has been circulating in the US swine population since the late eighty’s, however, recently the virus emerged worldwide, and it has been associated with several VD outbreaks in pigs in many of the major swine producing countries. Despite the recent surge in the number of cases of SVA, the factors underlying the emergence of SVA, as well the molecular basis of SVA interactions with the host remain unknown. The overall goal of this study was to improve the understanding of the SVA infection biology and its interactions with the swine host. The objectives of our study were: 1) To compare the pathogenicity and infection dynamics of a historical and a contemporary SVA strains (SVV 001 and SD15-26) and to evaluate cross-reactive immune responses; and 2) To investigate the role of apoptosis on infection and replication of SVA. To achieve the first objective, an animal study was performed in pigs. The animals were inoculated with SVA SVV 001 or SD15-26 and the animal were monitored for 14 days. Both SVA strains successfully infected all inoculated animals, resulting in viremia and antibody and cellular immune responses. SVA SVV 001 did not cause overt clinical disease with inoculated animals remaining clinically normal during the experiment, while SVA SD15-26 infection resulted in characteristic clinical signs and vesicular lesions. Levels of viremia detected in SVA SD15-26 inoculated animals were significantly higher than those detected in SVA SVV 001-inoculated animals. Differences in virus shedding were also observed mostly in nasal secretions, with SVV 001-inoculated animals shedding lower amounts of virus. Whereas similar levels of virus shedding were observed in oral secretions and feces. Neutralization- and -recall IFN-γ expression-assays revealed marked cross-neutralizing antibody and cross-reactive T cell responses between the two viral strains. To achieve the second objective, we investigated the host apoptotic responses during SVA infection and further dissected the interplay between the virus, host cell apoptosis and NF-κB signaling. First, we demonstrated that SVA infection induces apoptosis late during infection in vitro and in in vivo. Since NF-κB is one of the major players modulating host cell apoptosis, we assessed its activation in infected cells. We detected activation of NF-κB pathway early during SVA infection, while late in infection, a cleaved product corresponding to the C-terminus of NF-κB-p65 was observed in infected cells, resulting in lower NF-κB transcriptional activity. We showed that expression of SVA 3Cpro was associated with cleavage of NF-κB-p65 and Poly (ADPribose) polymerase (PARP), suggesting its involvement in virus-induced apoptosis. Most importantly, we showed that while cleavage of NF-κB-p65 is secondary to caspase activation, the proteolytic activity of SVA 3Cpro is essential for induction of apoptosis. Finally, we confirmed the relevance of late apoptosis for SVA infection through experiments using a pan-caspase inhibitor, indicating that SVA-induced apoptosis is probably involved in facilitating virus release and/or spread from infected cells Results from these studies provide important information on SVA infection and shed light on differences in biological properties and pathogenesis of contemporary and historical SVA strains, as well as on the role of apoptosis for SVA infection biology.

Library of Congress Subject Headings

Swine -- Virus diseases.
Swine -- Virus diseases -- Pathogenesis.
Swine -- Infections.
Swine vesicular disease.
Picornaviruses.
Host-virus relationships.
Cell death.

Format

application/pdf

Number of Pages

118

Publisher

South Dakota State University

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Rights Statement

In Copyright