Mycoplasma hyopneumoniae case positivity increased in August, reaching 26% in wean-to-market – the highest level observed in 2026 – while overall activity remained within the expected range, according to the latest Domestic Swine Disease Monitoring Report.
“The report shows lessened activity for influenza, but increased activity for porcine reproductive and respiratory syndrome (PRRS), porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV),” says Dr. Lisa Becton, DVM and associate director of the Swine Health Information Center (SHIC). “We’ve seen an increase compared to what we would expect in August, so that makes you reflect on what has changed. Some of the respiratory diseases are following typical patterns, where some of our enteric diseases are not.”
Becton believes this should lead producers to question farm biosecurity processes.
“The report indicates for PRRS, PEDV and M. hyo that it was among wean-to-market, and we already know that’s an area where biosecurity may not be as tight as it is in sow farms,” Becton says. “It highlights the continued need to be vigilant and assess how biosecurity could be enhanced in this age group.”
As the end of summer approaches, temperature variability and stress may start to increase as cooler weather sets in. It also marks the time for the start of manure application, which carries many disease risks as its removed from barns and applied to fields.
“This report doesn’t create or identify results that are necessarily unexpected, but rather it does identify the need to maintain vigilance, especially in our wean-to-market categories,” she says. “This monthly monitoring allows us to detect trends. We can detect diseases by age, state, production type, and that’s what’s really important because it gives us an idea where we need to focus our time, effort and research dollars.”
Consistency Over Complexity: Managing Biosecurity Costs
The decision to boost biosecurity can become a cost concern for some producers, Becton says.
“Think about filtration. That’s not an inexpensive process for installation,” she adds. “And if you don’t do all the other biosecurity things right, you can negate the filter’s biosecurity benefit to prevent diseases from coming into the farm. It doesn’t prevent the entry of diseases by people coming in without washing their boots or dragging in dirty coveralls or equipment.”
She urges producers to think holistically about wean-to-market sites and what each individual producer can do on their farms to reduce their risk.
“It doesn’t have to be complex,” Becton says. “It has to be consistent.”
Which PRRS Strains Are Causing the Most Problems?
In the August report, PRRSV variant L1C.5.32 was the most detected in the U.S., followed by L1C.5 and L1A.13.49. The states with the higher number of L1C.5.32 detections were Iowa, Illinois, Minnesota and Indiana.
“When we get each monthly report, we hope that there are no new strains on the list. But if there are newer strains that start to become more active across production, we need to know that, too, in order to take action,” Becton says.
States that identified first-time detections of PRRSV variants include:
- June 2026: 1K.4 in Indiana; 1A.29 in Missouri and 1H.48 in Pennsylvania
- July 2026: 1A.29 in Louisiana and 1C.2 in Tennessee
