Deadly bird flu has been found in raw cow’s milk and may be able to survive standard pasteurisation, a study suggests.

Scientists tested milk samples from herd infected with H5N1 in New Mexico and found high levels of the virus, even after it had been refrigerated at 4c (39F).

It means animals drinking the milk, including humans, stand a risk of catching it.

When mice were fed the untreated milk they showed signs of illness from the first day, and the virus was detected in their respiratory systems and other organs of their bodies.

The researchers heat-treated the milk at 72C, similar to how supermarket milk is pasteurised, for various lengths of time.

In the UK, milk must be heated for at least 15 seconds, and no longer than 25 seconds.

The researchers found the virus was reduced, but not eliminated, even after 20 seconds of heating. Only after 25 seconds was it destroyed.

They wrote in the New England Journal of Medicine: ‘Our data indicate that H5N1 virus in untreated milk can infect susceptible animals that consume it.

‘Heat treatment for 15 or 20 seconds reduced virus titers by more than 4.5 log units but did not completely inactivate the virus.

‘H5N1-Positive milk poses a risk when consumed untreated.’

However, the researchers admitted it was impossible for them to accurately replicate industrial pasteurisation methods in their lab. 

Raw milk is available in certain health stores, trendy coffee shops and direct from artisan dairies. 

The virus was confirmed in commercial poultry in England in February, however there have been no reported cases of the virus in UK cows.

Meanwhile, World Health Organisation disease expert Maria van Kerkhove said bird flu may be the cause of a future pandemic.

She said: ‘It's infected many different species. That's why we have a whole system in place to be prepared for this.

‘I'm not saying this to scare people, but for us, it's something that we have to be prepared for.

‘We have to think out of the box. We really prepare for what are the known threats, but also think about something different, perhaps waterborne or whatnot.

‘So for me, pandemics, unfortunately, are part of what we will deal with in our lifetimes. I don't believe [Covid] will be the last pandemic we will deal with in our lifetimes.’