SHIC-Funded SDRS Yields Valuable Influenza Surveillance Data

Influenza A virus is a significant respiratory pathogen affecting various species, including swine. The dynamics and diversity of IAV require ongoing surveillance to enhance understanding and generate solutions for control. A recent publication, led by PhD student Dr. Daniel Moraes under mentorship of Swine Disease Reporting System Principal Investigators Drs. Giovani Trevisan and Daniel Linhares at Iowa State University, reported influenza surveillance data gathered from the SDRS, a project funded by the Swine Health Information Center. Published in Frontiers of Veterinary Science in April 2025, results detail 20 years of compiled veterinary diagnostic laboratory data on IAV and provides unique insight into understanding its epidemiology.  

Using a comprehensive approach, this study aimed to characterize the macroepidemiological patterns of IAV detection utilizing PCR assays, including subtype identification, over the last 20 years. The findings offer valuable insights into IAV dynamics across the US, detailing its distribution by age category, specimen type, and seasonal trends. Specifically, samples submitted between January 2004 and December 2024 to VDLs participating in the SDRS were analyzed and revealed a substantial 31% of the 372,659 samples tested positive for IAV RNA.  

Regarding sample types tested for IAV, oral fluids (44.1%) and lung tissue (38.7%) emerged as the most frequently submitted sample types, indicative of their utility in surveillance. Notably, the wean-to-market category exhibited a higher positivity rate at 34.4% compared to the adult/sow farm category’s 26.9%, emphasizing the importance of this age group in IAV ecology. A similar phenomenon has been previously reported for PRRS and PED viruses. The study also revealed a consistent seasonal pattern, with IAV detection peaking in spring and fall and decreasing during the summer months. 

Further insight into IAV diversity was gained through subtyping of 118,490 samples. The most prevalent subtypes identified were H1N1 (33.1%), H3N2 (25.5%), and H1N2 (24.3%), with H3N1 detected at a much lower rate of 0.2%. Interestingly, mixed subtypes were identified in 5.4% of samples, with partial subtype detection in 11.5%. The presence of mixed IAV subtypes in individual samples, including lung tissue, nasal swabs, and bronchoalveolar lavage, provides evidence of co-infection with multiple IAV strains. For forecasting IAV trends, improved modeling methods were established to inform stakeholders of weekly changes in IAV detection patterns and enhance accuracy in predictive capabilities. 

This work underscores the importance of IAV as a major respiratory pathogen in swine and highlights the ongoing need for monitoring to understand its epidemiology. Specifically, this study highlights the indispensable role of laboratory submission data in robust IAV surveillance and macroepidemiological analysis. The consistent detection of mixed IAV subtypes in lung tissue further emphasizes the complex nature of IAV infections.  

As an outcome of the study, the authors recommend the establishment of standardized monitoring systems within VDLs, which will enhance the understanding of IAV in swine populations and enable more timely identification of surveillance trends. Overall, the collation of IAV detection data over 20 years within this study assists in informed decision-making based on the generated macroepidemiological information. Real-time updated IAV monitoring information is available in the SDRS website dashboards, and through SHIC’s monthly Domestic Disease Monitoring Reports.  

The Swine Health Information Center, launched in 2015 with Pork Checkoff funding, protects and enhances the health of the US swine herd by minimizing the impact of emerging disease threats through preparedness, coordinated communications, global disease monitoring, analysis of swine health data, and targeted research investments. As a conduit of information and research, SHIC encourages sharing of its publications and research. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Megan Niederwerder at [email protected] or Dr. Lisa Becton at [email protected].