Although porcine reproductive and respiratory syndrome (PRRS) numbers trended downward in July, the frustrating virus still tends to cast a “big, uncertain specter” in swine health,” says Dr. Lisa Becton, associate director of the Swine Health Information Center (SHIC). The latest SHIC Domestic Disease Monitoring Report shows PRRS variants continue to diversify and are being detected across more states.
Key PRRS Variant Highlights for July
- Most Detected Variant: 1C.5.32 (139 cases), heavily concentrated in IA, IL, MN, MO, IN, NC, OH, KS, OK, and SD.
- Other Top Variants: 1C.5 (37 cases) and 1A.13.49 (35 cases).
- New Regional Detections: Variant 1A.29 was detected for the first time in Louisiana, and variant 1C.2 made its first appearance in Tennessee.
Overall, 20.73% of 7,025 cases tested positive for PRRS in July, a moderate decrease from 25.72% of 7,275 in June. Read the full report here.
Disease on the Decline in July
Meanwhile, porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV) activity returned to the expected range in July after spending several weeks above expected levels earlier in 2026.
Overall, 5% of 4,342 cases tested PEDV-positive in July, a moderate decrease from 7.96% of 4,523 in June. Additionally, 1.86% of 4,296 cases tested PDCoV-positive in July, similar to 2.69% of 4,420 in June.
Mycoplasma hyopneumoniae activity decreased in July following elevated detection in June, while porcine circovirus type 2 (PCV2) activity increased compared to the previous month.
“This just continues to solidify whether it’s an emerging endemic disease or an emerging global disease, monitoring is so important,” Becton says. “If we’re not watching those trends and digging further into the virus charcteristics, we would never know these shifts are occurring. We’re not just looking at diagnostic results; we’re assessing clinically what animals are affected, age groups, sample types, and then investigating further into the genetics that could explain those trends. That’s a powerful piece of information all of us in the industry need.”
Why Influenza Numbers Are Lower This Summer
Influenza (IAV) activity also continued to decline, with case positivity in adult/sow farms dropping to 13%, the lowest July level recorded since 2014. In July, 21.65% of 1,963 cases tested IAV-positive, a substantial decrease from 27.5% of 2,182 in June.
IAV has largely stopped following predictable seasonal patterns and varies year-to-year, Becton says. Like PRRS, influenza viruses mutate often and can render existing vaccines ineffective, requiring careful management of vaccine schedules.
She notes the widespread presence of highly pathogenic avian influenza (H5N1) in dairy cattle has driven producers to reassess risk factors for transmission such as wild bird exposure through water systems and barns. Additionally, Becton says that ongoing research shows H5N1 can infect swine mammary tissue, and it has a different clinical signs for pigs experimentally infected than what is expected for endemic influenza viruses.
“Biosecurity remains our best defense,” she adds. “We do have targeted vaccines for endemic influenza viruses that are available, both commercially and as autogenous. But if the virus changes significantly, your vaccines may not work. Consider how you can maximize your vaccine schedules to what viruses you have, and it is also important to understand what phase of production infection occurs to help drive other management strategies and reduce virus impact.”
Rather than simply handing down biosecurity protocols, Becton urges veterinarians to explain the ‘why’ behind the rules to build stronger producer buy-in.
“If we continue to educate and explain how these steps reduce disease transmission, we can build a much stronger culture of biosecurity across the entire industry,” she says.
