Infectious dose of Senecavirus A in market weight and neonatal pigs

Authors: Buckley, Alexandra; Lager, Kelly

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2022
Publication Date: 4/29/2022
Citation: Devries, A.C., Lager, K.M. 2022. Infectious dose of Senecavirus A in market weight and neonatal pigs. PLoS ONE. 17(4). Article e0267145. https://doi.org/10.1371/journal.pone.0267145.
DOI: https://doi.org/10.1371/journal.pone.0267145

Interpretive Summary: Senecavirus A (SVA), also known as Seneca Valley virus, is one of multiple viral agents that causes vesicular disease or blister-like lesions in swine. Vesicular disease caused by these agents is grossly similar; therefore, the causative agent can only be identified by diagnostic testing. Foot-and-mouth disease virus (FMDV) is one of the viruses that causes vesicular disease similar to SVA. Since FMDV is not currently found in the United States (US), when a vesicle is observed an investigation must be performed to rule out the presence of FMDV. Senecavirus A continues to circulate in the US and the number of these investigations is rising, which costs both time and resources. A better understanding of the infectious dose of SVA could help direct control and prevention measures to reduce the spread of SVA. The objective of this study was to determine the infectious dose 50 (ID50) and minimum infectious dose (MID) of SVA in both finishing pigs and neonates. A 2011 SVA isolate was serially hundred-fold diluted to create four challenge inoculums ranging from 10E6.5 to 10E0.5 TCID50/ml for individually housed finishing pigs (n=4 pigs/dose) and serial ten-fold dilutions were used to create 6 challenge inoculums ranging from 105.5 to 100.5 TCID50/ml for individually housed neonates (n=4 pigs/dose). In finishing pigs, the ID50 and MID were both 1,260 TCID50/ml. In neonates the ID50 was 31,600 TCID50/ml, while the MID was 316 TCID50/ml. This work has demonstrated that biosecurity measures in the field to decrease viral exposure could aide in reducing the severity of infection and spread on the farm. In addition, understanding the minimum infectious dose of SVA can help producers and veterinarians in the swine industry focus their disease control and biosecurity measures on areas that carry the most risk of exposure of high levels of SVA.

Technical Abstract: Senecavirus A (SVA) is a picornavirus that causes vesicular disease in swine. With the spread of SVA around the globe, some countries free of foot-and-mouth disease (FMD) are experiencing an endemic vesicular disease in their swine populations, which adds to the time and cost burden of ruling out FMD every time a vesicle is observed since FMD and SVA are clinically indistinguishable. Understanding the pathogenesis of the virus and its ability to transmit to naïve populations is critical to formulating control and prevention measures. The primary objective of this study was to determine the infectious dose of SVA in finishing pigs and neonates. A 2011 SVA isolate was serially hundred-fold diluted to create four challenge inoculums ranging from 10E6.5 to 10E0.5 TCID50/ml. Four finishing pigs individually housed were intranasally inoculated with 5 mL of each dose (n=16). For neonates, serial ten-fold dilutions were used to create 6 challenge inoculums ranging from 105.5 to 100.5 TCID50/ml. Again, four animals in individual housing were challenged orally with 2 mL of each dose (n=24). Detection of SVA by PCR in collected samples and/or neutralizing antibody response was utilized to classify an animal as infected. The minimum infectious dose for this study in market weight animals was 1,260 TCID50/ml (103.1 TCID50/ml) and for neonates it was 316 TCID50/ml (102.5 TCID50/ml). Knowledge of the infectious dose of SVA can guide biosecurity and disinfection measures to control the spread of SVA.