Viruses in cows are more similar to viruses in birds than humans.
US research has found that H5N1 viruses in dairy cows are more similar to those sampled from birds than influenza viruses that are better at infecting humans.
The research from St. Jude Children’s Research Hospital revealed that avian influenza (bird flu) from the ongoing outbreak in US dairy cattle appears to be keeping its bird-infecting features, rather than adapting to “better” infect other mammals.
Bird flu
Since 2024, when scientists in the Tennessee hospital first detected H5N1 bird flu in dairy cattle, there has been fears that the virus would use cattle as a “bridge” to mutate and gain the ability to infect and spread into humans.
Researchers at the hospital tested a panel of these viruses from dairy cows, and found that the viruses had more molecular and biological features in common with avian than human flu viruses.
In addition, the viruses from cows could not transmit through the air between mammals, though direct infection of an individual human from close contact with infected dairy cattle is possible.
Corresponding author from the St. Jude department of host-microbe interactions, Richard Webby said: “We found that these flu viruses from cow udders are not under a lot of pressure to mutate to better infect other mammals such as humans.
“For now, the risk of becoming a pandemic threat to humans appears low, though the risk of direct infection for those working with these animal remains high.”
While they may not infect humans “efficiently”, according to the US researchers, viruses from dairy cows have already caused at least 41 in people through close contact with dairy cattle.
The scientists in St. Jude’s wanted to know if the viruses could spread between humans, so they studied a mammalian model of human influenza infection.
The research found that the models could not pass the bovine flu to each other through the air. However, these models could spread the virus through direct contact.
According to St. Jude’s, the lack of airborne transmission indicates a low risk of spreading between humans, but the other experiments suggest that there is still a threat of direct infection.
Infection prevention
As a result, the scientists looked to see if current interventions for flu could help treat such infections.
This process began by examining the immune molecules in the blood of people vaccinated against avian influenza.
If vaccines fail, then physicians will reach for antivirals to treat an infected individual.
According to the hospital, there are two antivirals used in patients with influenza, so the researchers measured how well both controlled H5N1 infections from the cow viruses in the lab, and studied genetic markers of treatment resistance.
The researchers explained that while results are encouraging, they do not mean that bovine viruses are “innocuous”, and that infected mammalian models still showed signs of sickness, as have some humans.
In addition, the virus continues to evolve, so the results from the research may not apply in the future if a new variant arises.
