By Giovani Trevisan, Guilherme Cezar, Christopher Rademacher and Daniel Linhares, Iowa State University

Endemic diseases are a constant burden to animal production. Animal health interventions rely heavily on diagnostic testing and testing results to support farm-specific production systems and regional and national animal health interventions. Organized animal health data hubs are extremely helpful in generating and providing information that decision-makers can use to intervene and contain the spread of diseases.

The Swine Disease Reporting System shares information on the activity of nine endemic and other emerging pathogens affecting the swine population in the U.S. Producer, veterinarians and farm anonymized data is sourced from six major swine-centric veterinary diagnostic laboratories, representing >97% of porcine samples tested in the National Animal Health Laboratory Network.

Porcine reproductive and respiratory syndrome virus, porcine epidemic diarrhea virus, porcine deltacoronavirus, Mycoplasma hyopneumoniae and Influenza A ended 2024 following the overall expected detection levels. However, the state-level activity of these pathogens has been above state-specific baselines in some regions.

Pathogen highlights

PRRSV

PRRSV continues to be the beast in the room and burdens the swine industry pretty hard. In October and November, the PRRSV reverse transcription polymerase chain reaction detection levels were above 46%, which was not seen since 2018 in the wean-to-market phase. In December 2024, the detection of PRRSV in the wean-to-market declined. Conversely, detection in sow farms is on the rise, igniting a potentially more significant problem for the upcoming months as weaned piglets reach downstream nursery and finishing farms (Figure 1).

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Figure 1: Monthly PRRSV RT-PCR detection monitoring according to state-specific baselines. States with detection above expected state-specific baselines are color-coded in dark red. State-specific monitoring is also available for Influenza A, Mycoplasma hyopneumoniae, porcine deltacoronavirus, and porcine epidemic diarrhea virus. Updated charts are available at the Swine Disease Reporting System webpage under the “Pathogen detection and monitoring at the state level” dashboard.

The PRRSV L1C.5 is the “elephant” in the room with little over 50% of all wild-type PRRSV ORF5 sequences detected belonging to this group (Figure 2). In Iowa, Minnesota, Nebraska and South Dakota, it is even higher, with a little over 60% of all wild-type being L1C.5. Still, nothing compares with Missouri, where 88% of all wild-type viruses are L1C.5. While regions like Arkansas, Colorado, North Carolina, Oklahoma, Kansas and Texas have been prosperous in keeping this virus out, L1C.5 continuous to pose an imminent threat that can`t be ignored.

Figure 2: Yearly number of PRRSV ORF5 sequences shared with the SDRS and its break down according to Lineages. Chart available at the Swine Disease Reporting System webpage under “PRRSV genotyping dashboard: RFLP and Lineages” dashboard.

Regional differences in terms of PRRSV detection are a reality. The L1A and L1Hs remain predominant in Indiana, Kansas, North Carolina, Ohio and Oklahoma. The L1C.2 became the predominant PRRSV detected in Illinois in 2024, and regional spread to Iowa and Minnesota spiked in 2024 (Figure 3). The variant 1H.18 has gained traction at the end of the year in Iowa and Minnesota, but also with first detection in Oklahoma, Ohio and Pennsylvania. Movement of PRRSV strains still occurs across regions, e.g., Colorado had one detection in 2008, 2017 and 2018 for an L1A PRRSV. However, after September 2024, 13 detections of the L1A occurred in Colorado, signaling a potential introduction of a new virus in the region.

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Figure 3: The three most frequently detected wild-type PRRSV ORF5 sequences detected by states according to lineage and RFLP. Chart extracted from page 3 of Swine Disease Reporting System PDF report 83 from January 7, 2025.

Enteric coronavirus

A veterinarian who graduated in 2021 and afterward has not seen TGEV detection in field samples since the last TGEV-positive sample dates back to March 2021. If no resurgence of this virus occurs, the industry may have one less bug to deal with. Detection of PEDV and PDCoV has followed the expected detection curves for 2024. Industry discussions around a potential elimination of PEDV gained traction in 2024, with resolutions supporting the elaboration of the PEDV elimination plan being passed at the American Association of Swine Veterinarians, the US Swine Health Improving Plan, and the US Animal Health Association meetings. SDRS data shows that the detection of PEDV is very dynamic, but a potential opportunity to elaborate customized regional plans to control this pathogen could be possible. In general, there are two groups of states with PEDV detection lower than 7% and another group with detection levels up to 30%, indicating an opportunity for regional control and elimination strategies. Importantly, in-house performed testing is not part of the SDRS data, and its inclusion would provide a more representative picture of PEDV activity.

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Mycoplasma hyopneumoniae

MHP is a major respiratory pathogen causing enzootic pneumonia, reduced productivity and increased costs in swine herds. The U.S. has implemented protocols to eliminate MHP from breeding herds. SDRS data shows a decline in positive submissions from 20.75% in 2019 to 11.4% in 2024 and sustained lower levels during the year for sow farms. Increased use of deep tracheal swabs and the lowest number of tissue-confirmed MHP cases in 2024 highlight progress. However, a rise in positivity in wean-to-market submissions in the year's second half raised concerns about biosecurity breaches. Still, no significant number of rebreaks in breeding herds have been reported so far. Continued efforts are needed to mitigate MHP’s impact and support eradication goals.

Influenza A virus

The swine industry continues to actively survey and monitor this pathogen, with over 2,000 cases tested monthly. Influenza A has followed the expected pattern of bi-seasonal activity with spikes in detection during Spring and Fall. Despite the reports of HPAI in backyard pig production, the data shared with SDRS has only detected endemic influenza A virus.

ISU VDL

Another pathogen highlight is disease diagnosis from ISU VDL has followed similar levels as previous years, with increased activity of respiratory pathogens diagnosis starting in September.

SDRS monitors porcine diagnostic testing and testing results in real time. The information generated is distributed to stakeholders for educational purposes to aid in making informed decisions about disease management and control by decision-makers. Stakeholders can visit the project SDRS website for real-time updates through project dashboards and sign up to receive the monthly reports and keep up to date on the SDRS reported trends. The SDRS is currently supported by competitive grants awarded by the Swine Health Information Center and the USDA National Institute of Food and Agriculture.