The bird flu strain found in a US cow that was flown to a UK lab for testing

Avian flu usually spreads by infecting wild birds and moving along migratory routes, but the virus that is currently running rampant in the United States is about to be transported across the Atlantic by plane.

This category A pathogen, which is now spreading among cows in the US, is being sent to a high-security laboratory in the UK so that experts can better understand the potential risks to humans and livestock.

Related: ‘The question is when to pull the trigger’: how prepared are we for human bird flu?

“It’s due to launch any day now,” Dr Ashley Banyard, a virologist at the UK’s Animal and Plant Health (Apha) laboratory in Weybridge, Surrey, said last week. “I saw the packaging instructions in my email this morning.” It is vital that this virus does not escape into the wider environment: worldwide, H5N1 has killed millions of wild birds and thousands of mammals.

Although bird flu is widespread in the UK, the specific genome being imported for testing is the only one known to infect cattle, and the only place where it has been recorded is in the US. “We want to know if there is something special about this particular genotype that has evolved,” Banyard said.

It is shipped in a small amount of liquid inside three tubes, with dry ice between layers – a bit like a Russian doll. Special courier costs hundreds of pounds to transport it safely door to door.

The virus made headlines in the United States in March after it was detected in dairy cows in Texas and Kansas, following widespread reports of a loss of milk production. Since then it has been reported across nine US states, with no sign of slowing down. Also detected in cats and humans, it was probably circulating for months before it was discovered.

“We’re hoping that the American situation will be further controlled and limited, and then we won’t see this virus in cattle in the future, but you never know with these things,” Banyard said.

Everyone who works in the Weybridge lab is counter-terrorist checked, and there are multiple levels of locked doors and key cards. “I know it’s kind of James Bond esque but it’s not real – they’re just labs,” Banyard said.

From Spanish minks to polar bears in the Arctic and seals in the Antarctic, the virus has killed a range of mammals, generally by eating infected meat.

The US outbreak has sparked alarm because it is the first time bird flu has been detected in a cow, and it is unclear how it got there. Because the virus can spread in dairy herds there is “tremendous concern” it could spread more easily in humans, according to the World Health Organization (WHO). The Director General said last week that the virus shows no signs that it has adapted to spread from person to person.

A peer-reviewed paper published earlier this month is the first to claim that the virus entered dairy cows through a single introduction from a wild bird, and that it is being transmitted from cow to cow. Milk is currently believed to be the main vector (possibly via milking equipment) and symptoms are mild, including reduced milk production and loss of appetite.

In the United States, dairy cows being moved across states must now be tested for bird flu. Health officials say it is okay to drink milk, provided it is pasteurized, a process designed to kill bacteria and viruses.

There are concerns that cows could be infected in other countries where they are not being tested, although Banyard is confident that it has not already happened in the UK. “We have infected more than 380 premises across the UK in the last two and a half to three years and we have seen no evidence of these symptoms in cattle,” he said.

Very few livestock animals are imported from the US, and migratory birds rarely bring avian flu viruses from the US to Europe because it is not a normal migration route. In the three years of this H5N1 outbreak, no North American strain has been found in Europe. “And everyone in Europe is looking,” said Professor Ian Brown, a virologist from the Pirbright Institute in Surrey.

Brown said it was surprising to see it grow in a dairy cow – “It shows us that it can get into niches you wouldn’t expect” – but this is another chapter in the evolution of H5N1, which has continued to surprise researchers the number. of the animals it can infect (at least 26 species of mammals are infected). “These are the early stages of an epidemiological investigation.”

Scientists need to understand the potential risks of bird flu to humans. “All eyes are on this internationally,” Brown said. For the virus to start spreading between people, it would have to undergo some genetic changes that would mean it can replicate in human cells.

Brown said people who work in close contact with dairy cattle should be monitored because they are the highest risk – more than 200 people in the US are being monitored. “We have to be vigilant. We need to make sure we are on top of tracking this so we see it early if the risk to people changes. That is very important.”

If bird flu started to spread between people, it would be a matter of considerable concern because the H5N1 virus has a high mortality rate. From 2003 to 2024, 889 cases were reported in 23 countries and more than half of those people died, according to WHO. Therefore, pre-pandemic vaccines are already stockpiled.

The virus is already spreading in ways it never has before. Professor Rowland Kao, an epidemiologist at the Roslin Institute at the University of Edinburgh, said: “Moving around the other animal could mean we’re throwing another animal into the mix… it creates another layer of unpredictability.”

This is the first time that an influenza A virus has been found in cattle, which “may pose threats to wildlife, livestock and possibly humans that we have not experienced before.”

Monitoring and data sharing – such as testing the US genome in UK laboratories – is vital to contain any potential outbreak. “We are a long way from a human pandemic,” Kao said. “But it brings things a step closer.”

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