Key Findings
- Researchers at The Ohio State University found that influenza D virus can replicate in human respiratory tract cells and lung tissue samples as effectively as influenza A viruses.
- The study, published in Proceedings of the National Academy of Sciences, tested several genetically distinct strains of influenza D isolated from cattle and pigs.
- Influenza D did not stimulate a robust antiviral immune response in infected cells, unlike influenza A.
- Human cells pretreated with interferon restricted influenza D growth, indicating that human cells have mechanisms to inhibit the virus.
Background
- Influenza D was first detected in animals in 2011. Cattle are considered the primary host, but the virus has also been found in pigs.
- Antibodies to influenza D have been found in some humans who work with cattle, but no active human infection has been confirmed.
- The study suggests influenza D has potential to spill over to humans, though no human cases have been identified.
"It seems like there are many animal species that are susceptible to influenza D viruses, suggesting that maybe they can evolve differently in different hosts. What's obvious is that zoonotic infections are happening."
Statements from Researchers
- Lead author Cody Warren said: "All of the viruses, despite their genetic distance from each other, had similar replicative capacity in these human cells and human tissues."
- Warren noted: "It seems like there are many animal species that are susceptible to influenza D viruses, suggesting that maybe they can evolve differently in different hosts. What's obvious is that zoonotic infections are happening."
- Co-author Andrew Bowman stated: "Flu D popped up in our samples and that led us to question what the risk is at the human-animal interface."
- Bowman added: "The currently held belief is that bovines are the natural host for flu D. So pigs may be a secondary host, or not."
"Those are gaps that we don't quite understand."
Implications
- The findings raise questions about whether human infections could be asymptomatic or if the virus could evade the immune system.
- Warren acknowledged: "Those are gaps that we don't quite understand."
- The researchers emphasize the need for surveillance and basic research to prepare for potential future emergence.
Funding
- The work was supported by the U.S. Department of Agriculture, the National Institute of Allergy and Infectious Diseases, the National Institutes of Health, and the Ohio State Enterprise for Research, Innovation and Knowledge.