The line separating America’s commercial swine herd from a devastating disease outbreak is thinner than many realize. Although the U.S. eradicated pseudorabies (PRV) and swine brucellosis (SBR) from commercial swine years ago, a reservoir persists in feral swine roaming the countryside.
While there is occasional spillover of infection to non-commercial, outdoor herds where contact with feral swine is possible, the confirmed case of PRV in a commercial herd in Iowa—the first since 2004—served as a reminder of the critical interface between wild pigs and domestic pigs.
“The April 2026 pseudorabies confirmation in a commercial herd in Iowa emphasizes the need for strict separation between commercial and non-commercial swine,” Lynn Wachtman, veterinary medical officer with USDA Animal and Plant Health Inspection Service Veterinary Services, said at the 2026 Allen D. Leman Swine Conference. “This detection also highlights the important role that surveillance programs play in detecting disease quickly and maintaining export markets.”
Inside the Nation’s Early-Warning Defense
USDA APHIS, in conjunction with state and industry partners, operates a national PRV and SBR surveillance program, which aims to demonstrate disease freedom in commercial swine herds and support disease control through detection of cases in herds at higher risk for infection. Wachtman says the USDA Federal Brucellosis Laboratory (FBL) conducts serologic screening for these diseases on specimens primarily collected at federally inspected, state-inspected or custom slaughter facilities, but may also be collected at aggregation points or farms. The National Veterinary Services Laboratories conduct confirmatory testing.
A 2017 USDA APHIS analysis indicated that testing 1% to 2% of breeding swine annually in the top 29 swine producing states, combined with targeted surveillance of higher-risk swine, was statistically equivalent to the Code of Federal Regulations (9 CFR 78.1) requirement for each state to annually test 5% of breeding stock.
She says this level of testing equates to an annual target of approximately 100,000 specimens. In March 2026, USDA APHIS reviewed the sensitivity and specificity of the current diagnostic testing algorithms to refine sample size estimates and determine disease detection probability based on the amount of ongoing testing.
Declining Samples, Shifting Odds
Between Jan. 1, 2018, and Dec. 31, 2025, the USDA FBL tested an average of 87,879 specimens per year. The total number of specimens tested decreased by an average of 4.8% year-over-year. In 2025, a total of 67,925 specimens were tested.
Specimens were heterogeneously distributed by state. The level of surveillance conducted in 2025 allowed for a 95% probability of detecting either disease when at least 1.25% of U.S. breeding herds contained at least one infected animal.
Balancing Feasibility with Confidence
Wachtman says the number of cases detected between Jan. 1, 2023, and Dec. 31, 2025, ranged from four to seven SBR cases per year and two to 13 PRV cases per year, and all were in non-commercial herds.
“Prevalence of pseudorabies and brucellosis in domestic swine populations is very low making it difficult to test enough samples to target current levels of disease circulation. There is a need to balance feasibility with confidence,” she says.
Still, Wachtman points out that the recent pseudorabies detection in a U.S. commercial herd highlights the need for federal, state and industry partners to continue working together to maintain the rigor and effectiveness of the national PRV and SBR surveillance program.
“The information gathered is critical to inform strategies, reduce the incidence of infection in non-commercial herds, and provide trading partners confidence that the U.S. commercial swine herd remains free of disease,” Wachtman says.
