A new lab study from Ohio State University suggests that influenza D, a cousin of seasonal flu that circulates in cattle and pigs, can replicate efficiently in human airway tissue and slip past some of the immune system’s early alarms. Combined with a CDC journal review published earlier this year, the findings have researchers warning that the virus could become a public health threat if it adapts to spread from person to person. Because hospitals and public labs do not routinely test patients for influenza D, scientists say it may already be circulating under the radar.
Lab tests show IDV can grow in human airways
In the new study, Ohio State researchers exposed human lung epithelial cell lines, well-differentiated airway cultures and precision-cut lung slices to a panel of livestock-derived influenza D strains. Across these models, they observed high infectious titers that were comparable to those seen with human influenza A.
The team also found that influenza D triggered much weaker interferon signaling and induced fewer interferon-stimulated genes than typical human flu, a pattern that could blunt early innate immune detection and give the virus more room to replicate before the body mounts a strong response. The work is currently available as a preprint, with full methods and data posted on PubMed Central.
CDC journal authors say the risk is real
In a separate review article in Emerging Infectious Diseases, authors concluded that “even the limited data regarding these novel, newly detected viruses indicate that they are a major threat to public health” and called for expanded surveillance at the human-animal interface.
Co-author John Lednicky cautioned that if influenza D or related animal viruses evolved the ability to spread easily between people, they could spark epidemics or even pandemics, a concern he also raised in a University of Florida news release cited by the paper.
Evidence people have already been exposed
Serology data suggest that people who work closely with cattle have already encountered influenza D. A 2016 cohort study published in J Clin Virol reported roughly 91 to 97 percent seropositivity among a small group of Florida cattle workers, far higher than in adults without livestock exposure.
Field and experimental work in Northeast China added more fuel to the concern. Researchers there documented airborne transmission of influenza D in ferret models and unusually high community seroprevalence in some areas, findings that suggest the virus can cross species barriers and may circulate beyond narrowly defined occupational groups. Those results were reported in Emerg Microbes Infect.
Testing gaps and environmental signals
Environmental surveillance has picked up influenza D genetic material in air samples collected inside airports and hospitals, evidence that the virus can show up in shared indoor air during routine monitoring efforts, according to data available on PubMed Central.
Despite those signals, the CDC journal perspective notes that “there is no routine screening for influenza D in humans,” and that diagnostic pipelines and vaccine development for this virus are still limited. That gap leaves public health officials with a significant blind spot when it comes to spotting any early shift toward sustained human-to-human spread.
What scientists recommend
The researchers behind the new lab work, along with authors of recent field and review papers, say the immediate to-do list is straightforward. They call for targeted surveillance of livestock and the people who handle them, standardized diagnostic tests that explicitly include influenza D, and laboratory screening of existing antivirals to see whether any are effective against the virus. Those priorities were echoed in studies that found airborne transmission in animals and high seropositivity in some human populations, published in Emerg Microbes Infect, which argue for catching any evolutionary leaps as early as possible.
For now, scientists say the immediate risk to the general public is still uncertain. Documented human infections have mostly been subclinical, without severe symptoms. Even so, the combination of efficient replication in human tissues, serologic evidence of past exposure and the current lack of routine testing is enough, in their view, to justify close monitoring.
Public health experts advise sticking with common-sense respiratory virus precautions during the season: stay home when sick, improve indoor ventilation where possible and keep recommended vaccinations up to date, while researchers continue to validate these findings through peer review and expanded surveillance efforts.
