Persistence and shedding of Senecavirus A in naturally infected boars

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In this recent publication from the Journal of Veterinary Diagnostic Investigation, Dr. Matt Sturos from the UMN Veterinary Diagnostic Lab shares a case report establishing the shedding of Senecavirus A through boar semen. This study highlights the importance of considering semen as a potential biosecurity risk in the case of a Senecavirus A outbreak.

Case description

  • Farm 1 is a 2,000-head farrow-to-wean farm in Minnesota that went through a Senecavirus A outbreak in 2017. Two boars showed clinical signs and were euthanized for further testing.
  • Farm 2 is a sow farm in Indiana that experienced a Senecavirus A outbreak in 2020. Semen was collected from 9 and then 16 boars. One boar was euthanized for further testing.

Findings

  1. Semen tested positive via PCR for up to 91 days after the clinical signs were noticed.
  2. Oral swabs and fecal swabs were negative via PCR whereas the testis and tonsils were positive up to 156 days after the clinical signs started.
  3. Virus isolation was successful from one of the boar semen sample.
  4. Histopathology showed segmental degeneration and atrophy of the germinal epithelium within the seminiferous tubules and multifocal lymphocytic orchitis in the testes.

At this time, it is still unclear what the primary source of the SVA RNA being shed in the semen is, but the testes seem the most likely in these chronically affected boars. This is supported by the testes having the lowest Ct values of all tissues tested when compared to other reproductive and systemic tissues.

Further details are available on the journal’s website.

Abstract

Senecavirus A (SVA) infection in pigs causes vesicular disease and results in a short viremia and transient shedding of the virus, mainly in oral fluids and feces. Here we describe the consistent prolonged shedding of SVA in the semen of 2 boars, and persistence of SVA within the tonsils and testes of 3 adult boars. Two SVA-infected boars that were identified on a Minnesota sow farm in 2017 shed SVA RNA in semen for >3 mo after an outbreak of vesicular disease had occurred on the farm. SVA was isolated from 1 semen sample collected 9 d after clinical disease began on the farm. The third SVA-infected boar was identified on an Indiana sow farm in 2020. All boars had SVA RNA detected in the testes and tonsils by RT-rtPCR, with lower Ct values obtained for the testes than from the tonsils. All boars had multifocal lymphocytic orchitis with segmental degeneration and atrophy of the germinal epithelium within the seminiferous tubules. One boar also had areas of seminiferous tubule collapse and interstitial fibrosis within the testes. In all boars, in situ hybridization demonstrated the presence of SVA mRNA within cells located basally in the seminiferous tubules of the testes, and within the basal surface epithelial cells, crypt epithelial cells, and subepithelial and parafollicular lymphocytes and histiocytes of the tonsil.