Scientists: H5N1 virus in cows takes 'dangerous' step toward infecting humans

Scientists have warned that the bird flu virus spreading in US farm cattle may have taken a "dangerous step" towards being able to infect humans via respiratory infections, compared to other strains.

The H5N1 virus has been confirmed in cattle on 140 farms in 12 states, and traces of it have also been found in pasteurized milk sold in stores.

The outbreak is believed to have started when cows on a Texas farm were infected with the virus from wild birds.

At least four people who work closely with animals have been infected, although their symptoms were mild and they did not transmit the virus to others.

A new study by scientists at the University of Wisconsin-Madison in the United States has shown that the new "cow virus" can bind to receptors on cells in the human respiratory system.

These receptors are how influenza viruses normally enter and infect human cells.

The H5N1 strain found in birds cannot do this, suggesting that the bovine virus has mutated.

The study also confirmed that the virus can be transmitted efficiently through contaminated milk.

Milk from an infected cow in New Mexico made mice and ferrets sick after they consumed just one drop. However, further tests on ferrets revealed that the virus cannot be effectively spread through breathing alone.

In the experiment, a sample of the H5N1 avian influenza strain was placed near healthy animals, but not close enough for physical contact. None of the four healthy ferrets became sick or showed symptoms.

Scientists later discovered that only one ferret produced antibodies to the virus, indicating that it had been infected.

Scientists say a virus that can spread easily through the air between humans would pose a greater pandemic threat than the current H5N1 virus.

Despite the good news, Dr Ed Hutchinson, from the Medical Research Council and the University of Glasgow's Centre for Virus Research, said there were still "reasons for concern".

“When they compared their cow flu isolate to avian flu, they found that it had already begun to acquire some of the characteristics that might be associated with the ability to spread effectively through respiratory infections in humans,” said Dr. Hutchinson, who was not involved in the study. “To be clear, it does not appear to be doing so yet, and none of the four human cases reported so far have shown signs of transmission.”

“However, the new H5N1 influenza virus will be more difficult to control, and more dangerous to humans, if it acquires the ability to spread effectively respiratoryly. While it is good news that cow flu cannot do this yet, these findings reinforce the need for urgent and decisive action to monitor this outbreak closely and try to control it as soon as possible,” he added.

It is worth noting that the H5N1 virus first appeared in 1996, but since 2020, the number of outbreaks among birds has increased dramatically. Since then, the virus has killed millions of birds and thousands of mammals around the world.

The World Health Organization (WHO) says the current risk to humans is low because there is no evidence yet of human-to-human transmission. But experts fear the sheer scale of the current outbreak could give the virus more opportunities to mutate, enabling H5N1 to spread more easily between humans.

The study was published in the scientific journal Nature.