Infectious Dose of a 2018 Senecavirus A Isolate in Neonatal Pigs

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.