Document Type

Thesis - Open Access

Award Date

2017

Degree Name

Master of Science (MS)

Department / School

Veterinary and Biomedical Sciences

First Advisor

Diego G. Diel

Keywords

infection dynamics, neutralizing antibodies, pathogenesis, picornavirus, Senecavirus A, SVA

Abstract

Senecavirus A (SVA) is a positive sense single-stranded virus that belongs to the genus Senecavirus within the family Picornaviridae. Senecavirus has been present in US swine population since 1988. However, there have been only a few reports of SVA associated with disease in last two decades. In late 2014 early 2015, a sudden increase in the number of cases of Senecavirus A associated with vesicular disease was observed in Brazil, the US and China. Affected pigs presented vesicles on snout, coronary band, and dewclaw. Additionaly, increased neonatal mortality has been reported in the field. Many aspects of SVA epidemiology, infection biology, and pathogenesis, remain unknown. Also, the cause(s) for the recent emergence of SVA in swine remains unknown. The objectives of our study were – 1) To investigate epidemiological factors that may contribute to SVA spread in the field and 2) To assess the pathogenesis and infection dynamics of SVA in finishing pigs. In our first study, a diagnostic investigation was conducted in swine herds affected by vesicular disease and neonatal mortality. SVA was detected and isolated from vesicular lesions and tissues of affected pigs, from environmental samples collected in affected and non-affected control farms. Among the environmental samples SVA was consistently detected in mouse feces and in a small intestine sample collected in one affected farm. Additionally, SVA RNA was detected in houseflies collected from both affected and unaffected farms. Whole genome sequence of the SVA isolated from the clinical and environmental samples was determined and phylogenetic analysis was performed. This analysis revealed that all the contemporary SVA isolates (obtained during 2014-2015) cluster together in a phylogenetic tree. However, a significant difference was found between contemporary and historical isolates of SVA and they form separate clades in the phylogenetic tree. On our second study, finishing pigs were experimentally infected with SVA SD15-26 strain to determine pathogenesis and infection dynamics of SVA. SVA inoculated animals showed vesicular lesions on the snout and feet by four days of infection. Infected animals presented clinical signs described in field outbreaks, including lethargy, lameness and anorexia. Additionally, SVA infected animals shed virus in feces, oral and nasal secretions and viable virus was isolated from oral fluid for up to 21 days postinoculation (pi). SVA RNA was detected in multiple tissues during the acute stage of infection, while it was detected in the tonsil of all infected animals up to day 38 pi. SVA inoculated animals developed an early and robust neutralizing antibody response against the virus. Neutralizing antibodies were first detected on day 5 pi. Infected animals recover within 2 weeks of infection. These studies provide significant insights the epidemiology, pathogenesis and infection dynamics of Senecavirus A infection in pigs.

Library of Congress Subject Headings

Swine -- Virus diseases.
Swine -- Virus diseases -- Pathogenesis.
Swine -- Virus diseases -- Epidemiology.
Swine -- Infections.
Swine vesicular disease.
Picornaviruses.

Description

Includes bibliographical references (pages 69-72)

Format

application/pdf

Number of Pages

85

Publisher

South Dakota State University

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Rights Statement

In Copyright