(NEW YORK) — Blood samples showed evidence of past bird flu infections in veterinarians despite the doctors never reporting symptoms or knowing they had been exposed, a new federal report published Thursday afternoon shows.
The findings suggest there could be people and animals with bird flu infections in other states that have not yet been identified, the authors said.
Investigators from the Centers for Disease Control and Prevention (CDC) collected blood samples in September 2024 from 150 veterinary practitioners who work with dairy cattle.
The practitioners were tested for bird flu antibodies that would indicate past infection and asked about their cattle exposure in the past three months. Additionally, their exposures since January 2024 were assessed.
At the time the samples were collected, bird flu infection in dairy cattle had been detected in 14 U.S. states, with four human cases in people with dairy cattle exposure in three states.
As of Thursday, 68 human cases have been detected in 11 states with exposures coming from dairy cattle, poultry farms, culling operations and other animals, according to CDC data. Most human cases have been mild and those patients recovered after receiving antiviral medication.
Three of the survey participants had antibodies in their blood indicating previous bird flu infection. None of them reported respiratory or influenza-like symptoms or received testing for influenza since January 2024.
All three practitioners worked with multiple animals, including dairy cattle. Two also worked with non-dairy cattle with one providing care to poultry and one working at livestock markets.
None worked with dairy cattle that had known or suspected cases of bird flu although one of the practitioners worked with poultry that had tested positive.
The practitioners all reported wearing gloves or a clothing cover while caring for cattle but did not report wearing respiratory or eye protection.
Additionally, one of the practitioners only practiced in two states — Georgia and South Carolina – -with no known bird flu infection in cattle and no reported human cases.
“These findings suggest that there might be [bird flu]–infected dairy cattle in states where infection in dairy cattle has not yet been identified, highlighting the importance of rapid identification of infected dairy cattle through herd and bulk milk testing as recently announced by the U.S. Department of Agriculture,” the authors wrote.
“Detection of [bird flu] antibodies in persons without reported symptoms suggests that surveillance of symptomatic exposed workers might underestimate human infection,” they added.
The authors highlighted the importance of getting the word out about recent recommendations from the CDC to offer post-exposure prophylaxis medication or treatment and testing to asymptomatic workers.
The report comes amid a second type of bird flu found in dairy cows for the first time, the U.S. Department of Agriculture announced last week.
This strain of bird flu, known as D1.1, has only ever previously been detected in wild birds and poultry, indicating that it has only recently spread to cows.
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