Bird flu ‘no longer just an avian virus’ as cases found in sheep and cattle

Bird flu should no longer be considered solely an avian virus due to the growing spread of the disease in mammals, a leading expert has said.

The world’s first-ever case of bird flu in sheep was identified in Yorkshire last week, while dairy farmers have been grappling with an outbreak of the virus in cattle in the US for the past year.

Dr Thom Rawson, an expert in avian influenza at the Jameel Institute at Imperial College London, said while the case of the sheep at the unnamed farm in Yorkshire would be a concern to the British farming industry, it had been diagnosed due to increased surveillance by British public health authorities as a result of the US cattle outbreak.

There have been dozens of human cases of avian influenza since the H5N1 outbreak began spreading in wild birds four years ago, but none so far have been as a result of passing between people, and the overall risk to the human population is classed as low.

This week the National Farmers’ Union is expected to raise concerns about the threat of bird flu and other animal and plant diseases to UK agriculture.

On Friday, the Government extended its ban on the commercial import of livestock and meat, including cattle, pigs, sheep, goats, deer and wild boar, to Austria following the spread of foot and mouth disease close to that country’s border in Hungary.

Bans on livestock and meat are already in place for Germany, Hungary and Slovakia.

UK farmers are also concerned about bluetongue and bovine TB.

The case of bird flu in a sheep in Yorkshire was on the same site as the virus had been confirmed in poultry.

The UK’s chief vet Christine Middlemiss said there was no evidence to suggest an increased risk to the nation’s livestock from bird flu as a result of the sheep case.

Rawson told The i Paper: “This is still predominantly within avian hosts, although that is spreading. The biggest cause for concern is how many more mammals we’re now seeing the virus in. 

“Without a doubt now, this can’t just be considered as solely an avian virus. We’re increasingly seeing it in mammals, and one of the biggest developments … was the first detected case in a sheep in the UK as well. 

“So it’s still quite a fresh, ongoing situation out there at the moment.”

Rawson said the Yorkshire sheep case showed that “smart surveillance” by Defra and the Animal and Plant Health Agency was working.

He added: “We’ve updated our testing regime in the UK, seeing how catastrophic this has been for the US dairy industry.”

Avian influenza in US cattle was discovered more than a year ago through testing of the cow’s milk, leading scientists to discover that the virus could replicate in mammary glands, rather than through the respiratory tract as it has done in birds.

Tests are underway to see if the virus in the Yorkshire sheep had infected its mammary tissue.

Rawson added that the World Health Organisation, which is monitoring the case of the sheep, wanted to stress that “smart surveillance” – testing targeted sites for bird flu – was the important message for farmers and livestock-keepers.

“You can’t test every animal on every farm in every country, how do we instead decide the best way that we can apply limited resources to the strong idea of what spillovers are occurring as soon as we can.”

There have been more than 40 human cases of bird flu in the US as a result of the cattle outbreak but all had developed from direct contact with the animals.

Rawson added that research at the Jameel Institute suggested that human cases in the US were passing the peak.

But he said that a fall in cases could be the result of less testing, due to cuts to America’s public health system under Donald Trump and Elon Musk.

The scientist said: “Things have been quietening down somewhat more than we would have thought.

“However, it’s not impossible to imagine that may be also linked to an awful lot of disruption in the public health system in America at the moment.”

Research at the end of last year suggested that bird flu is only one mutation away from being able to be transmitted between humans.

Rawson said there was so far no change to that picture.

He added: “We identified mutations that might improve binding to certain receptors to help improve the performance of replication in the human system, but there’s a lot more that goes into it than just one mutation.

“So far, we do not seem to have seen any additional further mutations. 

“The risk in terms of the wide scope of respiratory viruses still remains low in that regard.

“There is no further suggestion to think that we’ve moved along those stepping stones that you expect to see for a human pandemic.”

But Rawson said “there will rightfully be a concern” among farmers about the spread in mammals “simply because this has been such a huge change in our understanding of how this virus operates compared to two years ago”.

He added: “We’re very lucky that in the UK we have such good relationships and working experiences between civil service groups like APHA, FSA [Food Standards Agency], Defra and our farmers based primarily from experiences from BSE in the 80s and 90s, and that’s not a relationship that exists as strongly in the US.

“I do, at least as a scientist working in this field, have confidence that we do have a good eye on what is happening as this picture develops, which is the best position we could be in, and the best we can do then for farmers as well.

“In the poultry industry H5N1 has been bordering on an existential threat for some operations over the last five years.

“You certainly don’t want that to extend further into other animal systems… [but] I don’t think that we’re going to see in UK sheep something on the scale that the US has seen in its dairy cattle, primarily just due to the size of this industry. But we need more information.”