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Scientists comment on the first case of Avian Flu (H5N1) confirmed in a sheep in Yorkshire.
Dr Colin Butter, Associate Professor in Bioveterinary Science, University of Lincoln, said:
“The premises on which the single infected sheep was found had previously been home to birds that became infected with avian influenza, giving the possibility of faecal oral transmission of virus. This cross-species infection is unsurprising, given that birds and sheep share the same molecular receptor that allows virus to gain access, and then replicate in, the host animals’ cells. Whilst the prevalence of influenza in poultry and wild birds remains high, further limited incursions into farm species should be expected
“There is little immediate threat to humans from isolated infections of sheep, as normal cooking of meat and pasteurization of milk readily kills the virus.
“However, it will be important to understand if sheep can transmit the virus to other sheep as any further spread would allow genetic mutation and inter-species contact that might eventually lead to transmission into other species, including humans.”
Professor Ashley Banyard, Head of the National Reference Laboratory for Avian Influenza at the Animal Plant Health Agency, said
“The first global detection of HN51 in samples from a sheep is significant, but not totally unexpected given we have seen infected dairy cows and pigs in other countries. This detection is the result of an unusual exposure event to infectious viral material in a backyard setting where infected poultry had been previously housed.
“This detection was limited to a single animal and the infection pathway was most likely via co-located infected poultry. This underpins the importance of the UK’s approach in sampling and testing where there is evidence for increased risk of exposure to non-avian species following detection in poultry and underlines the importance of scrupulous biosecurity. The broader risk to sheep is considered very low”
Dr David Allen, Associate Professor in Virology, University of Surrey, said:
“The report from APHA & Defra of a case of H5N1 type influenza of avian origin in a sheep is noteworthy, as this is the first time the virus has been reported in a sheep. The case reported today was found through the routine surveillance programme, highlighting the importance of these surveillance systems.
“The H5 subtype of the influenza virus usually infects birds but can also infect mammals. There have been reports of avian-origin influenza virus infecting mammalian livestock in other countries: for example, avian-origin influenza has been detected in dairy cows in the USA, and last year the virus was detected in goats.
“In the case reported today, the sheep was on a premises where the avian influenza virus was present in captive bird flocks, which suggests transmission of the virus from these birds to the sheep. But as a single case in the sheep that has been managed, risks remain low.
“The quick identification of, and response to, the detection in a sheep has confirmed this is a single case, as further testing has shown no further infections on the affected premises. As such, risks to livestock remains low. However, it highlights the importance of maintaining strict biosecurity measures on premises.
“Avian-origin influenza viruses, like the H5N1 subtype, are primarily diseases of birds but have on rare occasions been reported in humans. Current evidence suggests the circulating avian-origin influenza viruses do not spread easily to humans, so the risk to the general public remains very low. However, but people should be aware of advice to not touch any dead or sick wild birds they find.”
Prof James Wood, Infectious Disease Epidemiologist at the University of Cambridge and Co-Director of Cambridge Infectious Diseases, University of Cambridge, said:
“This is a very important finding. It is the first case of a domesticated animal getting infected with avian influenza H5N1 over the 5 years or so of the current epidemic in wild birds and poultry. The case was detected in a sheep which reportedly had multiple positive tests in its milk and was on a farm clearly undergoing heightened surveillance as cases of the notifiable disease had been detected there in domestic poultry. Few details are yet available, but it seems reasonable to infer that the sheep was infected by close contact with infected birds or fomites from them on the same farm.
“Detection in milk is reported and some outlets report that lambs were tested and none found positive. It is not clear if this was a sheep being milked for human consumption or one that was only nursing lambs. No other sheep in contact were found to be positive.
“The case appears to have worrying parallels with the dairy cattle situation in the US, but also some reassuring differences. The case is one in which a mammary infection was found, as in the US cattle, but thankfully no within farm spread has been found. In the US, transmission between cattle is thought to have been mostly from the milking process. Differences in how sheep are milked (when they are) may make transmission risks lower than in dairy cattle – or the level of mammary infection may be different in sheep; it is hard to infer much from single cases. The surveillance in animals on the farm is a stark contrast to what has been done in the US; the simple act of stopping movement from infected farms can be expected to halt any farm to farm spread of this disease in sheep.
“While this is an important observation, it doesn’t change the global or national situation. Risks from avian influenza remain high and all care needs to be taken to ensure that there is no transmission from infected farms. Mammals in contact with avian influenza outbreaks will from time to time become infected and may become ill or die. Defra has announced this morning that they have updated their case definition for avian influenza in kept (and wild) mammals which will enhance their ability to control outbreaks. The heightened awareness of this potential transmission may result in other cases being found, should the current numbers of avian influenza outbreaks on poultry farms continue, despite the knowledge that strong biosecurity can prevent most of them. Pasteurisation of milk inactivates the risks to human health from avian influenza virus in it.”
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
Dr Colin Butter: I have no conflicts of interest regarding this statement.
Dr David Allen: I have previously worked for the predecessor organisations of UKHSA (i.e. Health Protection Agency and Public Health England) between 2009-2017.
Prof James Wood: James Wood is supported by BBSRC and Defra as part of a national consortium (Flu Trail Map) to address the challenges coming from avian influenza.
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.
For all other experts, no reply to our request for DOIs was received.