# Infectious Dose of a 2018 Senecavirus A Isolate in Neonatal Pigs

## TL;DR

This study found that a 2018 Senecavirus A isolate had the same infectious dose as a 2011 isolate, suggesting increased infectivity is not the reason for the rise in SVA cases since 2015.

## Contribution

The study determined the infectious dose of a post-2015 SVA isolate in neonatal pigs and compared it to a 2011 isolate.

## Key findings

- The 2018 SVA isolate had a minimum infectious dose of 102.5 TCID50/mL, similar to the 2011 isolate.
- Higher doses of the 2018 isolate caused clinical signs like diarrhea and lethargy in neonatal pigs.
- The results suggest increased infectivity is not the cause of the post-2015 rise in SVA cases.

## Abstract

Senecavirus A (SVA) was sporadically detected in swine samples in the United States starting in the late 1980s; however, in 2015 there was a sharp increase in the number of cases in the United States and around the globe. The purpose of this work was to determine if the infectious dose of a post-2015 SVA isolate was lower than previous work with a 2011 SVA isolate, which could help explain the sudden increase in SVA cases. The 2018 SVA isolate in this study had the same minimum infectious dose as prior work with a 2011 SVA isolate. This work provides support against the hypothesis that increased infectivity, and thus transmissibility, was the cause of the increase in SVA detections observed post-2015. Interestingly, animals receiving the highest doses of virus displayed clinical signs of diarrhea and lethargy, which is consistent with clinical signs reported in neonates during SVA outbreaks on sow farms. Previous experimental challenges have not been able to reproduce neonatal disease with SVA; therefore, this work can be used to help understand the pathogenesis of SVA in neonates.

Senecavirus A (SVA) is a picornavirus that causes vesicular disease in swine and has been associated with increased neonatal mortality. Although SVA had only been detected sporadically in the United States since the 1980s, there was a sharp increase in cases in the United States and around the world starting in 2015. The cause of this shift in SVA epidemiology remains unknown; however, changes in the virus that have resulted in enhanced infectivity may have contributed. The aim of this research was to establish the infectious dose of a post-2015 SVA isolate in neonatal pigs and compare its infectivity to previous work with a 2011 SVA isolate. A 2018 SVA isolate (SVA/KS/2018) was serially 10-fold diluted to generate six inoculums. Animals were individually housed with four pigs inoculated with 2 mL orally per dilution. Detection of SVA RNA in serum and swabs, as well as the presence of neutralizing antibodies, were used to classify the infection status of animals. The minimum infectious dose for SVA/KS/2018 in neonates was 102.5 TCID50/mL (2 × 102.5 or 632 TCID50/pig). This value is similar to the infectious dose determined for SVA/CAN/2011, thus providing evidence that the increase in SVA detections was not due to increases in infectivity of contemporary isolates. Neonatal mortality has not been experimentally reproduced; however, pigs inoculated with higher doses of SVA/KS/2018 developed diarrhea and mortality, suggesting increased virulence, which should be investigated further.