Study finds influenza A antibodies not uncommon in US cattle

A large study to gauge how susceptible US dairy and beef cattle are to influenza A viruses found that they are susceptible to human seasonal flu strains as well as swine influenza viruses, researchers based at the University of Missouri reported yesterday in mSphere.

Yesterday marked 1 year since H5N1 avian flu was first confirmed in dairy cattle, which occurred in a herd from Texas.

The new study is part of an effort to flesh out the extent of previous influenza A infection in cattle. Until the H5N1 outbreak in US dairy cows, cattle weren’t typically considered a natural host of influenza A viruses.

Using an enzyme-linked immunosorbent assay (ELISA) targeting the influenza A virus, the investigators tested 1,724 cattle blood samples collected from 15 states, though the majority were from Missouri, since January 2023. The samples were from more than 30 different cattle breeds.

Overall, nearly 34% of the blood samples were seropositive for influenza A, including 78 samples from 2024, and 508 from 2023.

No H5N1 found; both cattle sexes affected

None of the samples were positive for H5N1 avian influenza, which the group said was surprising. Positive samples were tested by hemagglutination inhibition (HI) assay, which revealed 45 were positive for 2009 H1N1 and H3N2 seasonal flu strains and swine H3N2 and H1N2 viruses. Some were positive for two or three of the influenza A viruses.