Influenza D study raises new spillover questions for veterinarians: full analysis
A new Ohio State-led study is sharpening concern around influenza D virus as a potential zoonotic threat. In work published in PNAS and announced April 24, 2026, researchers showed that influenza D strains collected from cattle and pigs could efficiently infect and replicate in human respiratory epithelial cells and human lung tissue, reaching levels comparable to seasonal influenza A viruses in the same experimental systems. (news.osu.edu)
That matters because influenza D has largely sat outside the spotlight since it was first detected in swine in 2011, even as evidence has accumulated that cattle are likely its main reservoir and that the virus is widespread in livestock. Prior reviews and CDC-linked publications have described influenza D as an emerging pathogen at the animal-human interface, and human exposure has been suspected for years through serologic studies rather than confirmed clinical cases. (news.osu.edu)
In the new study, the Ohio State team evaluated several genetically distinct influenza D isolates, including strains obtained through long-running swine influenza surveillance at county and state fairs. Using patient-derived airway epithelial cultures and precision-cut lung slices, the researchers found that influenza D replicated efficiently in both human and swine respiratory tissues. A notable difference from influenza A was the host response: influenza D grew well but did not provoke a robust interferon response in infected human cells. In separate experiments, however, viral growth was curtailed when cells were pretreated with interferon, suggesting human cells can restrict infection if antiviral defenses are activated early enough. (news.osu.edu)
That muted innate immune signal is one of the study’s most consequential findings. The authors say it raises two competing possibilities: influenza D infection in people could be mild or asymptomatic and therefore overlooked, or the virus may be especially adept at evading early immune detection. Ohio State’s Cody Warren said the “smoking gun” still missing is isolation of the virus from a person, despite evidence suggesting past exposure. (news.osu.edu)
Outside experts and prior public health literature provide important context. A January 2026 Emerging Infectious Diseases commentary from CDC-affiliated authors said several human studies suggest influenza D may cause subclinical infections, particularly among people with occupational animal exposure. That article also pointed back to a 2016 Florida seroepidemiologic study in which more than 97% of cattle workers had neutralizing antibodies to influenza D, compared with 18% of non-exposed controls. More recent work in cattle workers on U.S. farms has continued to find evidence of low-level neutralizing antibodies to influenza D, though not proof of active disease. (wwwnc.cdc.gov)
Why it matters: For veterinarians, this is less about immediate alarm than about risk framing. Influenza D is already relevant to bovine respiratory disease discussions, and Ohio State co-author Andrew Bowman noted the virus has also been associated with disease outbreaks in pigs. If a livestock-adapted influenza virus can replicate efficiently in human airway tissue while blunting early immune signaling, that raises practical questions for surveillance, worker health monitoring, diagnostic testing, and communication with pet parents and producers about zoonotic risk. It also reinforces the value of integrated surveillance across cattle, swine, fairs, and farm workplaces, especially as veterinary medicine is already operating in a heightened influenza awareness environment after the 2024 H5N1 dairy cattle outbreak. (news.osu.edu)
There are still important limits. This was a laboratory and tissue-model study, not evidence of sustained human infection or human-to-human transmission. No active human influenza D infection has yet been confirmed in the public literature cited here, and the study does not show that current field strains are poised to spread in people. But it does strengthen the biological plausibility of spillover and makes the surveillance gap more visible. (news.osu.edu)
What to watch: The next phase will likely center on expanded sequencing and surveillance in cattle and pigs, serology and respiratory sampling in exposed workers, and efforts to determine whether influenza D is already causing undetected human infections. Any future report of virus isolation from a person, or evidence of genetic change linked to adaptation in mammals, would mark a meaningful shift. (news.osu.edu)