Scientists comment on the first case of Avian Flu (H5N1) confirmed in a sheep in Yorkshire.
**Prof Ed Hutchinson, Professor of Molecular and Cellular Virology, MRC-University of Glasgow Centre for Virus Research (MRC CVR), said:**
“Influenza viruses are common in wild birds. Over the last five years, a particularly aggressive strain of the H5N1 avian influenza virus has spread through bird populations across the world. On the way, it has caused repeated ‘spillover’ infections of mammals: mammals that wouldn’t normally get avian influenza have caught the disease from birds. Usually these are one-off infections that don’t go any further, although last year the virus began to spread widely among dairy cattle in the USA, demonstrating the potential influenza viruses have for adapting to new species.
“The emergence of avian influenza in cattle last year was surprising, as normally cattle don’t catch this type of influenza (influenza A virus). Another animal we hadn’t previously thought of as a host for influenza A viruses is sheep, which makes this announcement of H5N1 influenza in a single sheep in Yorkshire startling. Sheep haven’t previously been thought of as hosts for influenza A viruses, although last year in the USA young goats did get infected with H5N1 at a farm in Minnesota – in this case, this was a one-off infection that didn’t go any further.
“The sheep was on a farm where avian influenza was present in captive birds, suggesting an obvious route of transmission from wild birds to captive birds to the sheep.
“The fact that the virus was detected in the sheep’s milk is also surprising. It suggests parallels to the ongoing H5N1 outbreak in dairy cattle in the USA, where the virus is spreading through cow’s milk. At the moment there is no evidence of any ongoing transmission from the sheep, and the case appears to have been contained.
“More work will be needed to understand what’s going on here – in particular to understand if this is a very rare or one-off event which happened because there was a lot of H5N1 around and this was just the wrong sheep in the wrong place, or whether sheep infections with H5N1 might become more common in the future. Ongoing surveillance will be needed to understand the risk this virus poses to the welfare of sheep as well as to food security.
“In terms of direct risk to humans, we know from the dairy outbreak in the USA that H5N1 in milk is a possible source of human infection. H5N1 can cause severe illness in humans and it is important to minimise the risk of farmed animals infecting them, although so far in the USA human cases of H5N1 contracted from cows in dairies have typically been quite mild. There is also a risk of H5N1 ‘breeding’ with human strains of influenza to produce a new human influenza virus. There is no evidence that this has happened anywhere with an H5N1 virus, but it is important that we work hard to keep that risk as low as possible.
“A single infected sheep does not pose a significant risk to humans, particularly because it looks as if the farmer, DEFRA and the APHA have worked together effectively to contain and monitor the situation. However, H5N1 is globally distributed in birds, and if it did become clear that this was not a one-off and that sheep are at risk of infection then this would have implications for surveillance and farm biosecurity in any country with sheep farming. For the time being, this is one to keep an eye on, but not to get too alarmed about.”
**Professor Ian Brown, Group Leader at the Pirbright Institute, said:**
“The detection of H5 highly pathogenic avian influenza (HPAI) in the mammary gland of sheep which has had close contact with infected birds is not an unexpected finding. Proactivity in looking for spillover to domestic mammals has been strengthened in the UK subsequent to the spread of infection amongst USA dairy cattle. The threat to animals and humans remains unchanged since such spillover we have learnt is possible when close contact occurs between multiple infected species. It is too early to consider whether such virus is capable of onward spread within sheep but this was an isolated small holding with a small number of birds and sheep. The pathways of spread of these viruses in the USA has been shown to be by movement of dairy cattle in commercial milking herds which appears not applicable in this single case of one animal becoming infected. It does emphasise the importance of separating species and maintaining good farm hygiene.”
**https://www.gov.uk/government/news/influenza-of-avian-origin-confirmed-in-a-sheep-in-yorkshire**
**Declared interests**
**Prof Ed Hutchinson:** I have received honoraria for work in a steering group of the Centre for Open Science (Open Practices in Influenza Research; 2021-2022) and on an advisory board for Seqirus (2022). I have unpaid positions on the board of the European Scientific Working group on Influenza and other respiratory viruses (ESWI) and as a scientific adviser to PinPoint Medical. I am part of FluTrailMAP(OneHealth), a UKRI-funded research consortium aiming to respond to H5N1.
**Prof Ian Brown:** IB receives research funding to study avian influenza in multiple hosts. IB is a member of the UK scientific committee ‘New and Emerging Respiratory Threats Assessment Group’. IB participates in UKHSA led fora that assess the risk to human health from avian influenza viruses.