The Swine Health Information Center (SHIC) received a call when vesicles were observed in the snout area of pigs on multiple farms in Iowa and Minnesota from January to April 2021. Investigators Jianqiang Zhang, Pablo Piñeyro, and others from Iowa State University (ISU) College of Veterinary Medicine worked on the case. A total of 133 swine vesicular cases with pig ages of three to 6.5 months from Iowa farms were submitted to the ISU Veterinary Diagnostic Lab. All were foot-and-mouth disease virus (FMDV) PCR negative but they were also negative for Senecavirus A (SVA) and other known vesicular viral pathogens, leaving the causative agent(s) unidentified. When standard diagnostic protocols did not reveal satisfying information about the cause, a request for diagnostic fee support was reviewed and approved by SHIC.
Follow-up investigations on the selected cases were conducted. These cases were also negative for other known vesicular viral pathogens swine vesicular disease virus (SVDV), vesicular stomatitis virus (VSV), and vesicular exanthema of swine virus (VESV). No significant bacteria growth was found from the selected vesicle swabs, suggesting bacteria probably were not the major causative agents. The investigators initiated the SHIC diagnostic assistance request because the known causative viral pathogens of vesicular lesions in pigs – FMDV, SVDV, VSV, VESV, and SVA – each pose a threat to the US swine herd. Currently the US is free of FMDV, SVDV, and VESV; these vesicular disease agents are considered foreign animal disease (FAD) pathogens in the US. VSV is still occasionally reported in the US and SVA is currently endemic in US swine. Complicating diagnostics, the vesicular lesions caused by FMDV, SVDV, VSV, VESV, and SVA are clinically indistinguishable.
Introduction of FMDV would devastate the US pork sector. So early detection and recognition of FMDV is critical to minimize the virus spread and economic burden. However, the endemic infection of SVA may reduce vigilance and result in the assumption that the presence of vesicular lesions is due to SVA so the vesicles would not be reported to State or Federal animal health officials; this would put the early recognition of FMDV at risk.
In summary, no clearly identified infectious causative agent for these vesicular cases has been identified. Nevertheless, the approaches and methods established in the current project can be applied for investigating similar cases in the future studies. It is frustrating for veterinarians, producers, and diagnosticians that the reason(s) for these observed swine vesicular lesions have not been identified although many efforts have been made in regards to sample collections and laboratory testing. However, in order not to miss detecting the true FAD pathogens causing vesicular lesions (e.g. FMDV), when vesicular lesions are observed in pigs, differential diagnosis should still be conducted. In this study, researchers focused on exploring the infectious agents potentially causing vesicular lesion. But, possible non-infectious factors may need to be investigated in the future.
SHIC, launched by the National Pork Board in 2015 solely with Pork Checkoff funding, continues to focus efforts on prevention, preparedness, and response to novel and emerging swine disease for the benefit of US swine health. As a conduit of information and research, SHIC encourages sharing of its publications and research. Forward, reprint, and quote SHIC material freely. SHIC is funded by America’s pork producers to fulfill its mission to protect and enhance the health of the US swine herd. For more information, visit http://www.swinehealth.org or contact Dr. Sundberg at firstname.lastname@example.org.