Senecavirus A- a study in immunogenicity, seroprevalence, pathogenesis, and transmission

Houston, Elizabeth
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Senecavirus A (SVA), formerly known as Seneca Valley Virus, is a single-strand, positive-sense RNA virus of the family Picornaviridae associated with recent outbreaks of idiopathic vesicular disease and increased neonate mortality in several swine producing countries. SVA is clinically indistinguishable from foot-and-mouse disease and other vesicular diseases, and increased incidence has been seen in the United States and other swine producing countries since 2014. Diagnostic testing must be utilized to confirm infection. The VP1 protein of SVA is a component of the viral capsid which has been used in serologic testing and proven highly immunogenic in other members of the Picornavirus family. Affected and non-affected animals from areas of clinical outbreak have been proven seropositive for IgG against SVA-VP1. In this study, an ELISA using VP1 was completed to determine the seroprevalence of virus antibody in United States’ swine. A mouse model was explored for use in pathogenicity and transmission. SVA polyclonal antibodies and SVA recombinant VP1 monoclonal antibodies were generated and characterized through ELISA, western blot, IFA, and viral neutralization.

Serum was collected from 2,433 clinically healthy sows and 3,654 clinically healthy grower or finisher pigs residing at 219 unique commercial swine production sites. SVA seroprevalence was evaluated by SVA rVP1 ELISA and SVA IFA. The estimated seroprevalence for grower-finisher pigs and sows was 12.2% and 34.0%, respectively. The herd prevalence was 42.7 % for grower-finisher farms and 75.8% for sow farms. The SVA rVP1 ELISA and SVA IFA exhibited a fair (sows) and moderate (grower-finisher) agreement at the herd level, while a fair agreement was observed at the individual level for both pig categories evaluated. The McNemar’s test was significant at the individual and herd level (p < 0.05). In this study, we demonstrated the presence of SVA IgG antibodies in pigs from clinically healthy grower-finisher and sow herds. These results suggest that SVA is circulating subclinically in sow farms and grower-finisher pig farms in major swine producing-states in the United States.

Five strains of mice were injected subcutaneously with virus. Then, route of inoculation was explored. Animals were monitored daily. Samples were tested by PCR, ELISA, and IFA to examine viral presence. No mouse showed clinical signs. However, feces and tissue of infected animals tested positive for virus specific nucleic acid. Seroconversion and a transient viremia occurred in mice inoculated by subcutaneous or intraperitoneal route. Mice develop subclinical infection when inoculated with SVA and may play a role in the transmission of SVA as a vector or reservoir for disease.

Eighteen epitopes of the VP1 protein were formed and their reactivity tested through indirect and blocking ELISA. Polyclonal antibodies and monoclonal antibodies were generated and utilized to identify reactive epitopes of the SVA VP1 protein. Four regions of the SVA-rVP1 protein showed high reactivity in multiple testing platforms. Results suggest that immune response generated by SVA-VP1 in mice can be defined by a set of linear epitopes that may be involved in the activity of antibody.

Epitope mapping, Mouse model, Senecavirus A, Seroprevalence, SVA VP1 ELISA