Senecavirus A in the environment of sow slaughter plants

Authors: Buckley, Alexandra; HOFFMAN, KYLE - Orise Fellow; Faaberg, Kay; HUMPHREY, NICKI - Animal And Plant Health Inspection Service (APHIS); KORSLUND, JOHN - Animal And Plant Health Inspection Service (APHIS); Lager, Kelly

Submitted to: American Association of Swine Veterinarians Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: 11/15/2022
Publication Date: 2/27/2022
Citation: Devries, A.C., Hoffman, K., Faaberg, K.S., Humphrey, N., Korslund, J., Lager, K.M. 2022. Senecavirus A in the environment of sow slaughter plants. American Association of Swine Veterinarians Annual Meeting. 22 June 2022. https://doi.org/10.3389/fvets.2022.923878.
DOI: https://doi.org/10.3389/fvets.2022.923878

Interpretive Summary:

Technical Abstract: Introduction Senecavirus A (SVA) infection in swine can lead to the development of vesicular lesions that are clinically indistinguishable from foot-and-mouth disease (FMD). FMD is not currently in the United States; therefore, a foreign animal disease investigation (FADI) must be performed every time a vesicular lesion is observed in swine to rule out FMD. With the increase of SVA cases in the US since 2015, there has been a corresponding increase in FADIs. A large portion of these investigations have been centered at sow slaughter plants, with some plants requiring investigations weekly. These investigations are both a time and economic burden and may result in complacency in reporting vesicular lesions in swine. The objectives of this study were to understand the environmental burden of SVA in slaughter plant lairage, correlate PCR, VI, and swine bioassay results, and compare 2020 SVA sequences to previous SVA isolates. Materials and Methods Four sow slaughter plants participated in the study: Plants 1-3 were experiencing a high incidence of FADIs due to reports of vesicular lesions and Plant 4 reported no FADIs. Swab samples were collected from the environment including flooring, waterers, and gating, as well as swabs from the coronary bands of pigs that did not have vesicular lesions, on a regular basis between June and December of 2020. Swab samples were tested for SVA nucleic acid by PCR and live virus by virus isolation (VI) on swine testicular cells over three passages. PCR and VI results were used to select samples to test via swine bioassay to correlate PCR results to VI results and infectivity in swine. Eighteen samples were used to inoculate individually housed pigs (2 pigs/sample). Blood and swab samples collected from animals were tested for SVA by PCR and a serum virus neutralization (VN) assay was performed to determine neutralizing antibody response. Finally, two isolates were chosen from plants 1-3 (n=6 total) for next-generation sequencing. A phylogenetic analysis was performed with all other whole-genome SVA sequences available in GenBank. Results Plants 1-3, high FADI incidence plants, consistently had SVA PCR positive samples collected from the environment throughout the sampling period, whereas Plant 4, no reported FADIs, was negative for SVA by PCR in all tested samples. Combined PCR data from Plants 1-3 showed that August had the highest percentage of positive samples between the months of June and December. Swab samples collected from the floor of lairage were the most common positive sample type collected and had lower Ct values compared to the other environmental sample types. As expected, samples with lower Ct values were more likely to be VI positive. 80% of samples with PCR Ct values less than 28 were VI positive whereas only 42% of samples with Ct values between 28 and 31 were VI positive. Finally, 5% of samples with Ct values greater than 32 tested VI positive. Eighteen samples with Ct values ranging from 24 to 33 were used to inoculate pigs for a swine bioassay. Although half of the samples were VI positive, only one sample with the lowest Ct value (24.2) was able to infect piglets and produce a neutralizing antibody response. Sequences generated from slaughter plant samples collected from different states in 2020 all clustered together (98.2% nt identity) as well as with other 2017 US isolates. Conclusion This study demonstrated that SVA is circulating in the cull sow market chain and can be found in the environment of slaughter plants. A better understanding of the epidemiology of SVA in the marketing chain may help reduce disruptions related to FADIs and direct control measures to reduce the spread of SVA.