Cases of humans contracting bird flu from cows are underestimated: CDC

The US Centers for Disease Control and Prevention (CDC) says there are more livestock industry workers infected with the H5N1 strain of bird flu than early estimates estimated. In a control trial with dairy workers in Michigan and Colorado, two of the states most affected by the flu, an infection rate was found to be 7%. Before the emergence of this new strain, the virus infection rate in agricultural workers was 0.6% worldwide.

The spread of the highly pathogenic 2.3.4.4.b strain of the H5N1 virus on dairy farms began in March 2024. The most recent reports indicate that the infection was latent and unidentified since December 2023. This was the first time the virus characteristic of poultry managed to infect cows. Traces of the pathogen even reached supermarket milk in several states, although only unpasteurized dairy proved dangerous.

The outbreak among dairy cattle was contained and product supply was never at risk. During the bird flu crisis, industry workers were the most forgotten element in medical and media coverage. According to the magazine Science46 human infections with avian flu were officially reported, 45 of which were directly linked to contact with poultry and livestock. The sample recently obtained by the CDC reveals a disturbing picture and suggests that the real number of human infections could be higher.

Workers had bird flu and didn’t know it

For two months, the CDC collected blood from 115 workers at farms affected by the H5N1 virus, with the intention of identifying antibodies against some of the most contagious clades of the pathogen. Of all of them, eight showed that they had had an infection and only four remembered any associated symptoms. Those who had antibodies were workers who milked cows or cleaned the rooms where the process was carried out.

So far, cases of infection have been mild or asymptomatic. There is also no evidence to indicate human-to-human transmission. Scientists recommend not letting our guard down. A random mutation in the bird flu virus could change its behavior and turn it into a transmissible human disease with pandemic potential.

“This finding highlights the need to actively monitor exposed workers by assessing for the presence of any mild symptoms and providing a safe environment that encourages reporting of even mild illness and allows for prompt treatment with antivirals to prevent progression to serious illness, without risk of repercussions in terms of job security and compensation,” the CDC explained in its report.

There is evidence to affirm that the avian influenza virus is transmitted efficiently and sustainably in mammals. The clade that affected dairy cows in the United States is the same one that has been present in polar bears, cats, foxes, mice, ferrets, dogs and even sea lions.