HAIRS risk assessment: avian influenza A(H5N1) in non-avian UK species

Question 1

About the Human Animal Infections and Risk Surveillance group

Accepted Answer

This document was prepared by the UK Health Security Agency (UKHSA) on behalf of the joint Human Animal Infections and Risk Surveillance (HAIRS) group.

HAIRS is a multi-agency cross-government horizon scanning and risk assessment group, which acts as a forum to identify and discuss infections with potential for interspecies transfer (particularly zoonotic infections).

Members include representatives from:

UKHSA
the Department for the Environment, Food and Rural Affairs (Defra)
the Department of Health and Social Care (DHSC)
the Animal and Plant Health Agency (APHA)
the Food Standards Agency
Public Health Wales
Welsh Government
Public Health Scotland
Scottish Government
Public Health Agency of Northern Ireland
the Department of Agriculture, Environment and Rural Affairs for Northern Ireland
the Department of Agriculture, Food and the Marine, Republic of Ireland
Health Service Executive, Republic of Ireland
Infrastructure, Housing and Environment, Government of Jersey
Isle of Man Government
States Veterinary Officer, Bailiwick of Guernsey

Question 2

Version control

Accepted Answer

Date of this assessment: July 2023

Version: 2.0

Reason for the assessment: first confirmed detections of avian influenza A(H5N1) in non-avian UK species (for example red foxes, Eurasian otters, harbour and grey seals); concerns for mammalian adaptation of avian influenza A(H5N1) virus.

Completed by: HAIRS members

Non-HAIRS group experts consulted:

UKHSA’s Acute Respiratory Infections team
Selene Huntley (Public Health Scotland)
Christopher Williams (Public Health Wales)

Date of initial risk assessment: June 2023

Reason for update: inclusion of new detections of avian influenza A(H5N1) in humans in the UK, and domestic animals (cats and dogs) in Europe.

Information on the risk assessment processes used by the HAIRS group can be found on GOV.UK.

Question 3

Summary

Accepted Answer

Avian influenza (AI) is an infectious disease of birds caused by the influenza A virus. Birds are the hosts for most AI viruses (AIV), and a variety of influenza subtypes, including AI A(H5N1), can be found in birds, particularly in waterfowl and shore birds. Domestic poultry are especially vulnerable, and the virus can rapidly cause epidemics in flocks. In October 2020, highly pathogenic AI A(H5N1) clade 2.3.4.4b was detected in Europe, after re-assortment of AI A(H5N8) with wild bird lineage N1 viruses. Since October 2021, AI A(H5N1) clade 2.3.4.4b has become the dominant AI subtype detected in wild and captive birds across Europe and the UK, with a relatively stable genotype.

The virus has now been reported from wild birds and poultry across Africa, Asia, North and South America, Europe and the Middle East. Globally, there has been an increased spillover to non-avian species including wild and captive terrestrial and marine mammals, and domestic pets, likely as a result of the increased environmental pressure from the thousands of wild birds infected, rather than as a result of increased viral affinity for mammalian cells.

Positive detections of AI A(H5N1) have been identified in a range of animals, mostly from the Carnivora family. In the UK, and as of March 2023, retrospective testing of samples collected since 2021 revealed positive detections in red foxes, Eurasian otters, common and grey seals, harbour porpoises and common dolphins, as well as a single event in captive South Africa bush dogs (Speothos venaticus). These were the first detections of AI A(H5N1) in non-avian UK species. Although these findings appear sporadic and isolated incidents, potential mammal-to-mammal transmission of AI A(H5N1) has recently been described in farmed mink in Spain, with genetic analysis revealing an uncommon mutation (T271A) in the PB2 gene which may enhance influenza A viral activity in mammalian host cells.

Detections of AI A(H5N1) in domestic cats (in France, Italy and Poland) and 5 dogs on a single poultry establishment (in Italy) have been reported, although such instances remain rare. The Poland cases have created a lot of interest as the source of infection has not been identified and the companion animals concerned (33 tested positive to date) were from multiple sites across Poland, were both indoor and outdoor cats, some exposed to raw pet food or wild birds and others not. Sequences of viral isolates from infected cats contain the common mutation, E627K in the PB2 gene, as well as the less common K526R, which has been detected in wild bird viral isolates.

More recently, Finland reported that 12 fur farms tested positive for AI A(H5N1). Most farm blue foxes, but also silver foxes, mink and raccoon dogs. The farms house between 3,000 and 50,000 animals. Generally, the first signs of infection were an increase in mortality in a few animals, as well as lethargy, neurological symptoms and diarrhoea. The source of infection is not yet known, although in one instance, a mass mortality event in black headed gulls was reported near one of the farms. Sequencing has been completed, and there were 2 markers in the cleavage site of increased mammalian cell affinity found in one sequence. All sequences aligned with those of wild birds, particularly strains found commonly in Europe in gulls.

Where AI A(H5) subtypes circulate in poultry or wild birds, then sporadic human cases should not be unexpected in people with close contact or high levels of exposure. This is particularly evident for Asian lineage AI A(H5N1), with 868 human cases, including 457 deaths, being reported from 21 countries between January 2003 and January 2023. Where Eurasian lineage AI A(H1N1) clade 2.3.4.4b is concerned, from 2020 to the end of December 2022, 6 human cases were reported, globally. All these cases had exposure to infected poultry. To date, there are no reported transmission events of AI A(H5N1) from non-avian infected species to humans.

This risk assessment will focus predominantly on AI A(H5N1) clade 2.3.4.4b as this is the dominant subtype detected in wild and captive birds across Europe and the UK at the time of writing.

Assessment of the risk of infection in the UK

Probability

General UK population: Very Low

The probability of infection would be considered Low for those exposed to infected live or dead non-avian species.

Impact

The impact on the general UK population would be considered Very Low, while it would be considered Low for higher risk groups (for example individuals with occupational exposure to infected non-avian species and/or immunocompromised or paediatric cases).

Level of confidence in assessment of risk

Satisfactory.

The majority of mammal cases are of the order Carnivora. While they may not all be recognised as commonly predating live or dead avian species, direct contact with a contaminated environment is also a possible transmission route. Without direct observational studies or environmental sampling in areas in the vicinity of known infection, it cannot be proven that mammal-to-mammal transmission is not occurring.

Given human detections of AI A(H5N1) clade 2.3.4.4b are rare, there is a paucity of evidence on what risk factors may increase disease susceptibility, severity and poorer clinical outcomes in human cases. For those cases reported, clinical disease has ranged from mild to severe. There is possible under-ascertainment of cases, particularly in instances where mild disease manifests.

Actions and recommendations

While there have been no reported incidents of people becoming infected as a result of direct contact with an infected wild mammal, captive mammal or companion animal, procedures to reduce human exposure to non-avian species potentially infected with AIV should be implemented, to minimise the risk of zoonotic infections. Members of the public should be discouraged from touching dead or sick animals. Pet owners should be encouraged to speak to their private vet if they are concerned about clinical signs in their companion cat, dog or ferret and are aware it has had contact with wild birds. If a member of the public observes an animal they deem in danger or distress, they should contact an appropriate helpline for advice and assistance (for example the RSPCA in England and Wales, the SSPCA hotline in Scotland and the USPCA in Northern Ireland).

Individuals who come into close contact with wildlife potentially infected with AIV as part of their work should be trained in the use of appropriate personal protective equipment (PPE), including aerosol-related respiratory precautions, to mitigate against the risk of zoonotic infections. Further information on working with AIVs is outlined in guidance published by the Health and Safety Executive (1).

In Great Britain, the APHA wildlife expert group maintains close interactions with non-governmental organisations (NGOs), including rescue centres. Where appropriate, NGOs should be encouraged to collect and submit samples from sick or dead non-avian wildlife to APHA Weybridge diagnostic laboratories for testing, of which AI A(H5N1) should be a considered differential, so as to be alerted to changes in viral epidemiology and potential risk. Additional information can be found on GOV.UK:

Question 4

Step 1. Assessment of the probability of infection in the UK human population

Accepted Answer

This section of the assessment examines the likelihood of an infectious threat causing infection in the UK human population. Where a new agent is identified there may be insufficient information to carry out a risk assessment and this should be clearly documented. Please read in conjunction with the Probability Algorithm (Annexe A).

Is this a recognised human disease?

Outcome

Yes/No.

While AI A(H5N1) is considered a disease in animals, there have been rare human infections, linked to exposure to infected birds. There is no evidence of human-to-human transmission of AI A(H5N1).

Quality of evidence

Satisfactory.

AIVs typically infect a large range of avian species, but also demonstrate the ability to infect mammalian animal hosts and thus pose a potential zoonotic risk to humans. Gradual changes in AI genomes over time, through mutation or genome reassembly, have resulted in several AI subtypes that are either circulating or newly emerging with the potential to trigger global health threats to mammals (4). Although AIVs rarely infect people, human cases have occurred following close contact, predominantly with infected birds, by inhaling droplets or dust containing the virus and/or contact with surfaces contaminated by an infected bird’s saliva or excreta (5). There is currently no evidence that AI can be transmitted to humans through the consumption of contaminated poultry products (6).

AIVs are classified into subtypes according to the combinations of different viral surface proteins hemagglutinin (H) and neuraminidase (N). They are further categorised into either high pathogenicity (HP) or low pathogenicity (LP), indicated by the severity of disease and mortality caused in chickens in a laboratory setting (7). Most AIVs cause no or mild illness, such as fever or conjunctivitis, in humans. However, subtypes including Asian lineage A(H5N1), A(H5N6) and A(H7N9) are known to have the potential to cause severe disease in humans, with mortality rates of up to 50%. While these subtypes do not easily infect people and have not acquired the ability to cause sustained transmission among humans (8), they are considered subtypes of public health concern.

Since December 2019, HPAI A(H5N8) has been detected in Europe, Central and East Asia, and the Middle East. HPAI A(H5N1) and A(H5N5) viruses have emerged from reassortments between HPAI A(H5N8) clade 2.3.4.4b viruses and other low pathogenicity avian influenza (LPAI) viruses found in wild bird reservoirs. In October 2020, HPAI A(H5N1) clade 2.3.4.4b was detected in Europe, after re-assortment of AI A(H5N8) with wild bird lineage N1 viruses. Since October 2020, this clade has also been detected in Africa and Asia and was introduced into North America at the end 2021 through infected wild bird migration. Since Autumn 2021 there has been domination of the HPAI A(H5N1) clade 2.3.4.4b viruses with a relatively stable genotype (9). These viruses continue to diversify genetically and spread geographically. From 2021 to 2022, Europe and North America have observed their largest and most extended epidemic of AI with unusual persistence of the virus in wild bird populations.

From 2020 to the end of December 2022, 6 human cases of AI A(H5N1) clade 2.3.4.4b were reported to the World Health Organization (WHO) from China (n=1), Spain (n=2), the UK (n=1), the US (n=1) and Vietnam (n=1) (10). Cases within Spain and the UK were asymptomatic. The US case reported fatigue. The case in Vietnam recovered from severe disease, while the case reported from China resulted in a fatality. Available viral sequences from these human cases did not show markers for mammalian adaptation nor for resistance to neuraminidase inhibitors (such as oseltamivir) or endonuclease inhibitors (such as baloxavir). All the cases had exposure to infected poultry (11).

In January 2023, Ecuadorian health authorities notified WHO of a human infection caused by AI A(H5), in a 9-year-old child hospitalised in a critical condition. This was the first reported case of human infection caused by AI A(H5) virus in the Latin America and the Caribbean region (12). Despite several sequencing attempts, no viral sequences from the H5 human case in Ecuador were recovered (13). AI A(H5N1) clade 2.3.4.4b was reportedly circulating in wild birds and poultry in the same area at the time.

On 8 March 2023, China’s Centre for Health Protection of the Department of Health announced they were monitoring a human case of AI A(H5N1) on the mainland (14). The case, who had exposure to live domestic poultry before the onset of her symptoms on 31 January 2023, was admitted to hospital for treatment on 4 February 2023 in a serious condition. Media reported that the case was infected with AI A(H5N1) clade 2.3.4.4b (15).

On 29 March 2023, the National Focal Point for the International Health Regulations of Chile notified the Pan American Health Organization and WHO of the first human case of AI A(H5N1) in the country (16). The case, a 53-year-old man without comorbidities from the Tocopilla commune in the Region of Antofagasta, developed symptoms on 13 March 2023 (cough, odynophagia, and dysphonia), and at the time of writing remained in respiratory isolation with mechanical ventilation. Viral sequencing confirmed clade 2.3.4.4b HA and was determined to be the same genotype that has been detected in most wild birds in South America. The virus was 99% identical to many viruses identified in AI A(H5N1) infected wild birds in Chile. Analysis of the HA gene showed that the virus lacked amino acid changes that improve recognition of mammalian receptors or fusion of the viral membrane with the host endosomal membranes (17).

Within the UK, 4 detections of AI A(H5N1) clade 2.3.4.4b in humans have been reported during 2023 (as of 10 July 2023); all in England. The detections were identified through enhanced surveillance of people exposed to AI (for example poultry workers), which commenced in March 2023 (38). It is unclear whether these cases were legitimate infections, or a result of contamination of the respiratory tract.

There is no evidence of human-to-human transmission of AI A(H5N1) clade 2.3.4.4b viruses and human cases are very rare given the number of exposures which are likely to have happened in the last 2 years.

Is this a zoonosis or is there zoonotic potential?

Outcome

Yes.

Quality of evidence

AI A(H5N1) from birds: satisfactory.

AI A(H5N1) from non-avian species: low.

Since the start of the AI outbreak in October 2021 to 25 July 2023, 349 cases of AI A(H5N1) clade 2.3.4.4b were confirmed in poultry and other captive birds in the UK. The risk of AI is a global issue. The latest figures show that Europe has reported nearly 3,600 outbreaks in poultry and more than 24,700 detections in wild birds across 37 countries. There have also been recent cases reported in North America, South America, Middle East, West and Southern Africa and Southeast and Central Asia. From 1 October 2022, through the APHA found-dead wild bird surveillance scheme, as of 25 July 2023, there have been 1,436 findings of AI A(H5N1) clade 2.3.4.4b in wild birds, in 425 locations involving 58 bird species in 84 counties across the UK.

Through samples collected as part of the routine surveillance programme for wild mammals undertaken by the APHA Diseases of Wildlife Scheme (DoWS), AI A(H5N1) has been detected in animals that were found dead, namely:

6 red foxes (Vulpes vulpes) – 4 in England, one in Wales and one in Scotland
5 Eurasian otters (Lutra lutra) – 4 in Scotland and one in England
3 harbour seals (Halichoerus grypus) – in Scotland
5 grey seals (Phoca vitulina) – one in Scotland and 4 in England
one harbour porpoise (Phocoena phocoena) – in England
one common dolphin (Delphinus delphis) – in England

In addition, AI A(H5Nx) has been detected in one grey seal (Phoca vitulina) (in England) and one common dolphin (Delphinus delphis) (in England). For animals collected since 1 October 2022 (the current outbreak season), there have been a total of 8 positive detections in wild mammals, in 8 locations, involving 5 species in 7 counties. There has been one incident of captive mammals – South American bush dogs in a zoological collection – which had died suddenly following possible exposure wild bird or gamebird meat.

HPAI viruses, particularly A(H5) subtypes, are remarkable because of their expanding non-avian host range (18). For example, AI A(H5N1) has caused severe and sometimes fatal disease in several naturally infected species (bears, bobcats, bottlenose dolphin, coyotes, a leopard, opossums, skunks, raccoons, sealions and seals) (19).

Where AI A(H5) subtypes circulate in poultry or wild birds, then sporadic human cases should not be unexpected in people with close, unprotected contact or high levels of exposure. This is particularly evident for AI A(H5N1) due to the Asian lineages, with 868 human cases, including 457 deaths, being reported from 21 countries between January 2003 and January 2023 (20). Where reported, all these cases had exposure to infected poultry.

To date, there are no reported transmission events of AI A(H5N1) from non-avian species to humans.

Mammalian viral adaptation and changes to viral pathogenicity

AIV transmission from avian to mammalian species may play an important role in the evolution of new mammalian viral strains (21). Following interspecies and sustained transmission of AI in a new host population, viral adaptation may alter the transmissibility and/or pathogenicity of the virus in both terrestrial and marine mammals (22).

LPAI viruses have demonstrated the ability to transmit from birds to mammal populations including swine, horses, mink, whales and common seals, spreading beyond the respiratory tract in some of these species and resulting in severe disease and mortality (18). Following increased awareness for potential spread of AIV to other hosts, additional surveillance and analyses have been established to identify subtypes infecting novel host species. Those have included cats, dogs and marine mammals (23).

An outbreak of AI A(H5N1) was reported in a mink farm in Spain in October 2022 (24). The farm had nearly 52,000 American mink (Neovison vison) placed in 30 barns. On 4 October 2022 an increase from 0.2 to 0.3% mortality to 0.77% was identified, triggering testing for SARS-CoV-2 and other respiratory viruses. Real-time polymerase chain reaction (PCR) tests were positive for HPAI A(H5N1) from oropharyngeal swabs of 2 animals. Increased mortality was observed between 17 and 23 October 2022 (4.3%) and additional sampling of 13 animals in areas with the highest mortality was undertaken. Reverse transcription polymerase chain reaction (RT-PCR) was positive for oropharyngeal swabs from 9 of 10 animals, rectal swabs were positive for the same 9 animals and 3 other animals were positive for lung samples. Virus sequence of the HA gene showed that 4 samples clustered closely to sequences from European gull samples from various countries (the AIV48 or BB strain), including Spain, during 2022. Amino acid comparison to the wild bird sequences also detected consistent changes from non-synonymous mutations resulting in threonine to alanine at position 271 (T271A) in the PB2 gene, as well as some other changes (M317V in the PB1 gene, M86T in the PA gene, F74S and V163L in the NA gene, D43G in the NS2 gene and P20L in the PB1-F2 gene). The T217A change would result in some changes in the polymerase activity enhancing activity in mammalian cell lines and has been reported from another wild mammal with A(H5N1) infection, a polecat. The other mutations have not been characterised in terms of biological impact.

Of the 12 workers on the farm, 11 had close contact with the mink and all were asymptomatic and tested negative for AIV.

No source or spread pathway has been confirmed. However, the sequences aligned closely with wild bird sequences and it would be a highly probable pathway given the attraction of mink farms for wild birds that scavenge the feed. Another source of infection, such as poultry origin feed, cannot be ruled out. Aerosol transmission between the mink would be likely given the positivity of oral-pharyngeal and lung swabs and the ‘hotspots’ seen within the barns of the increased mortality. However, faecal-oral or indirect transmission pathways from handling animals, or exposure to a common source over time cannot be excluded.

In Finland, a similar situation has occurred recently, with 12 fur farms being identified with AI A(H5N1) animals, following an increase in mortality and reports of clinical signs, including lethargy, neurological signs and diarrhoea. Another 9 farms are under investigation. Most farms were in 2 regions in the west of the country, which housed between 3,000 and 50,000 animals, mostly blue foxes, but also mink, silver foxes and raccoon dogs. The source of infection is not known, but dead wild birds were found around farms and a recent mass mortality event of black headed gulls had been reported near one premises. Full viral sequencing has been completed, and the genotype identified as BB (which is also known as AIV48 in the UK or the A/gull/France/22P015977/2022-like genotype) in which 2 adaptations to mammalian cells were observed. In samples from one fur animal farm with blue foxes and mink, the PB2-E627K mutation has been found. In samples from another blue fox farm, the PB2-T271A mutation has been found, and as noted above, this has been linked with increased replication in mammalian cells (potentially an enhancer for respiratory droplet transmission) and therefore could link to increased shedding. Not all animals affected had direct contact with one another, so animal-to-animal transmission has not been proven (Information provided by the Finnish Ministry of Agriculture and Forestry to the European Commission).

Neither the E627K nor the T271A mutation have been observed in any sequences from wild gulls, other wild birds or mammals in the UK, although E627K has been reported in a single poultry sequence (Alex Byrne, Ashley Banyard personal communication).

However, for increased infectivity and transmissibility and associated sustained risk to public health, several mutations in combination will likely be required (Ian Brown, personal communication).

In 2023, a large die-off of over 500 sealions was reported in Peru (25, 26). Since November 2022, a large mortality event of over 22,000 birds over 4 weeks in several coastal areas of Peru had occurred, rising to an estimated 50,000 dead birds. Over a period of 5 weeks (January to February 2023), 634 sealions (Otaria flavescens and Arctocephalus australis species) were found dead. Clinical signs included tremors, convulsions, paralysis, respiratory signs including nasal and buccal secretions. Most were female (which is probably indicative of the population and behaviour at this time of year, rather than dimorphic susceptibility) and several abortions were also recorded.

Samples were taken from various organs and rectal, nasal and oral swabs from 6 Otaria flavescens. All 6 were positive by RT-PCR for AI A(H5N1). A further 3 sealions and a dolphin from other regions which were found dead also tested positive for AI A(H5N1). The clinical signs of systemic infection, pneumonia and acute encephalitis are suggestive of HPAI infection and the high mortality in wild birds including sea birds, is evidence of exposure.

It has not been confirmed at this point whether there is mammal-to-mammal transmission through direct (such as nose-to-nose), aerosol, faecal-oral or indirect pathways. Further investigation into the viral sequences from one dolphin, one sea lion and 6 seabirds showed half the genome segments are of Eurasian origin and the other half are North American (26). However, none contained the E672K, D701N or K702R mutations normally linked to increased pathogenicity and mammalian adaptation, but this was a very small selection of sequences.

A mass mortality event was declared in the north-east US, involving 164 harbour and 11 gray seals in Maine during June and July 2022. Swab samples were collected from 41 of those animals and 17 out of 35 harbour and 2 out of 6 gray seals were positive for AI A(H5N1). Respiratory symptoms were observed with a subset of neurologic cases, although most stranded seals were deceased. The respiratory tract was the most consistent source of reverse transcription PCR–positive samples from affected seals (15 out of 19 nasal, 16 out of 19 oral, 6 out of 19 conjunctiva, and 4 out of 19 rectal samples) (48). There were concurrent findings in the area of known and suspected HPAI infection among terns, eiders, cormorants, and gulls. The authors conclude that there were likely at least 2 spillover events from wild birds, that mammal-to-mammal transmission was unlikely to be the source of infection and that there were only 2 sequences with either E627K or D701N mutations of the PB2 gene and therefore only limited evidence of mammalian adaptation.

A recent study in Canada of 40 AI A(H5N1) viruses from mammals found dead or euthanised at wildlife rehabilitation centres between April and July 2022 revealed that, in 17% of sequences, substitutions in the polymerase gene indicative of increased binding to mammalian cells was observed. Samples were taken from foxes, skunks and mink (27).

The most common mutations observed were E672K and E672V, both of which are associated with increased virulence, and D701N, which is implicated in expanding host range. Other mutations were also observed, albeit rarely, in internal gene segments. The phylogenetic analyses revealed that while all were 2.3.4.4b clade, 4 groups could be identified, one of which was wholly Eurasian and other 3 were reassortments with North American and Eurasian viruses (27).

In 2023, Poland reported multiple independent findings of AI A(H5N1) infection in cats living in different cities and towns across Poland, over the short time period of a few weeks. Over 33 cats so far have tested positive, but as this is a non-reportable infection in cats, there is likely to be under-reporting. Epidemiological investigations continue but there is no common source identified yet. Some cats had no access to outdoors and some were exclusively fed commercial shelf stable pet food. Others were fed raw pet food or raw poultry meat and had access to the outdoors. Of the viruses sequenced, they all belonged to the CH genotype (most closely related to the AIV09 genotype) and there were 2 mutations in the PB2 gene, E627K and K526R, indicating limited mammalian adaptation. Cats were observed with neurological signs, such as difficulty breathing, epilepsy and blindness, as well as lethargy and weight loss.

In Europe, both France and Italy have reported rare spillover cases in cats or dogs at poultry farms (Avian Influenza - WOAH - World Organisation for Animal Health). While Canada and the US have also reported cases in cats and dogs over the last 2 years.

Is the disease endemic in humans within the UK?

Outcome

No.

Quality of evidence

Good.

In January 2022, a laboratory confirmed human case of AI A(H5) (neuraminidase confirmation unknown) was reported for the first time in the UK. The case lived in the South West of England with a large number of captive birds (mostly waterfowl) that were allowed access to the dwelling house. The birds displayed onset of illness on 18 December 2021 and subsequently tested positive with HPAI A(H5N1). Genomic analysis of isolates from the infected birds demonstrated no strong correlates for specific increased affinity for humans. The human case remained clinically asymptomatic and no subsequent human-to-human transmission was detected (28).

Between May and July 2023, UKHSA reported 4 detections of AI A(H5N1) virus in exposed persons on farms in England where A(H5N1) was also confirmed in the poultry on site (38, 46, 47). All detections were identified as part of an ongoing enhanced surveillance study of asymptomatic workers exposed to premises infected with AI. It is unclear whether these were legitimate infections or not (in other words, it could instead be due to transient mucosal contamination of the nose with virus particles).

Although there is limited seroprevalence data available on AI A(H5) subtypes and clades in humans, WHO states that population immunity against AI A(H5N1) clade 2.3.4.4b virus haemagglutinin is expected to be minimal (11).

Is the disease endemic in animals within the UK?

Outcome

No.

Quality of evidence

Satisfactory.

AI A(H5N1) is not considered endemic in the UK, and while outbreaks in birds can occur at any point in the year, the UK typically experiences a seasonal increase of AI associated with incursions of infected wild migratory birds during the winter. Infected migratory birds can subsequently infect local and sedentary wild bird species, poultry or other captive birds. This can result in local transmission either directly between birds or indirectly by birds encountering environmental contamination, including faeces and feathers from infected birds. Where infected birds are present, then transmission to other species, including mammals, may occur. For example, in coastal regions, contact between marine mammals (for example otters and seals) and infected seabirds could lead to potential transmission events.

In the UK, there have been detections of AI A(H5N1) in red foxes (Vulpes vulpes), Eurasian otters (Lutra lutra), harbour seals (Phoca vitulina), grey seals (Halichoerus grypus), common dolphins (Delphina delphis) and a harbour porpoise (Phocaena phocaena). All animals were found dead and were not found as mass die-offs; some were tested retrospectively after submission through the diseases of wildlife scheme. These small number of cases are not unexpected, given their scavenging behaviour and close contact with waterfowl. The finding of AI A(H5N1) in captive bush dogs in a zoological collection in March 2023 was likely linked to consumption of infected wild waterfowl, and the cases were limited to a handful of bush dogs in a single group.

Globally, there have been limited reports of transmission between mammals despite the increase in mammalian infections. Affected mammals include:

Felis catus (domestic cat)
Panthera tigris (tiger)
Panthera pardus orientalis (Amur leopard)
Lynx rufus (bobcat)
Puma concolor (mountain lion)
Canis lupus familiaris (domestic dog)
Canis lupus (grey wolf)
Vulpes vulpes (red fox)
Vulpes lagopus (Arctic fox – captive morphs)
Canis latrans (coyote)
Speothos venaticus (bush dog)
Neovison vison (mink)
Viverridae (civet)
Mustela furo (ferret)
Martes americana (American marten)
Mustela putorius (polecat)
Pekania pennanti (fisher)
Mephitis mephitis (skunk)
Didelphis virginiana (Virginia opossum)
Procyon lotor (racoon)
Nyctereutes procyonoides (raccoon dog)
Ursus americanus (American black bear)
Ursus arctos (brown bear)
Ursus arctos horribilis (grizzly bear)
Ursus arctos middendorffi (Kodiac bear)
Ursus thibetanus (Asiatic black bear)
Phoca vitulina (harbour seal)
Halichoerus grypus (grey seal)
Arctocephalus australis (fur seal)
Phocoenidae (porpoise)
Phocoena spinipinnis (spiny porpoise)
Lagenorhynchus acutus (white-sided dolphin)
Delphinus delphin (common dolphin)
Tursiops (bottlenose dolphin)
Otaria flavescens (sea lion)
Enhydra lutris (sea otter)
Lontra felina (marine otter)
Lutra lutra (Eurasian otter)

For up-to-date information on affected bird species and mammal spillover, see the FAO website Bird species affected by H5Nx HPAI.

There is also some limited evidence of serological positivity in 2 non-carnivore species, during the HPAI A(H5N8) epizootic in 2020 in Europe: Sus scrofa (domestic pig) and Equus asinus (donkey) (29 to 31).

The possibility of the pig acting as a reservoir for infection and presenting a risk of viral reassortment between swine influenza and avian influenza viruses has long been considered a potential risk (32). However, there is also evidence that pigs are not highly susceptible to infection with AI A(H5N1) viruses of the Asian strains (33). For this reason, if pigs are present on any confirmed poultry premises in the UK, an epidemiological sample will be tested for evidence of infection or exposure. None have tested positive in any of the administrations covered by the HAIRS membership.

The findings in domestic or companion cats and dogs is not entirely unexpected as rare spillover events. However, the source of infection is still not understood for the multiple independent findings in Poland. Raw pet food is becoming more popular and may be a cheaper alternative to commercial shelf stable pet food in some circumstances, nevertheless this product should be made from animals destined for slaughter and suitable for human consumption. While Poland has reported some wild bird findings in recent weeks, these are not in the same diverse locations as the cat cases, nor do they feature the same strain. Epidemiological investigations are continuing.

There is an evidence gap identified for the role of rodents in transmission of AIV on poultry farms. There is no evidence and a lack of testing of rodents in the current epizootic, but there is experimental data for infection of various rodents with AIVs (34, 35). It is accepted that a poultry farm is susceptible to commensal rodent infestation, as are colonies of breeding birds, and rodents are frequently observed on poultry farms with poor biosecurity.

Are there routes of introduction into animals in the UK?

Outcome

Yes.

Quality of evidence

Satisfactory.

The UK typically experiences a seasonal increase in AI incidents associated with incursions of infected wild migratory birds during the winter months. After the 2021 to 2022 season (usually October to April), cases in wild birds and poultry continued over the summer, particularly in sea bird breeding colonies. This same situation was observed in sea birds across Europe. A working hypothesis is that the HPAI A(H5N1) virus has persisted in the environment at far higher levels than any of the previous years’ strains. Combined with a lower infectious dose requirement and a largely naïve sea bird population meant introduction into these colonies of breeding birds had a greater impact than ever seen before. Large numbers of dead birds in inaccessible places were observed and the virus continued to circulate in the sea birds, resulting in spillover into poultry farms outside the normal season. This high level of environmental contamination and high number of wild bird carcases would have increased exposure for wild mammals.

The presence of AIVs in released game birds over the summer could also have contributed to the infection pressure for wild mammals which would usually predate this population; between 40 to 50 million gamebirds are released in Britain each year for the shooting season, many of which will be predated. Once birds are released from their pens, they are no longer considered kept birds and therefore the (former) keepers are not required to report suspicion of infection, which means there is likely to be under-ascertainment of cases.

Mammals can be exposed through one of several pathways: consumption of infected birds or eggs; consumption of contaminated products, aerosol transmission from infected birds and/or contact with secretions from infected birds (Figure 1).

For mammal-to-mammal transmission to occur, it will depend on the level of contact between the mammals and the effective population size for viral circulation as well as adaptation.

Figure 1. Exposure routes of AIV from infected wild birds and/or poultry to mammals and humans

Are effective control measures in place to mitigate against these routes of introduction?

Outcome

No.

Quality of evidence

Satisfactory.

While there are control measures in place for domestic poultry outbreaks which require depopulation and safe disposal of all birds, followed by cleansing and disinfection and prevention of scavenging (36), there are no measures which are applied to wild birds, to prevent scavenging or environmental contamination. As incursion into the UK is most likely through the movement of wild birds, rather than the trade in live poultry or poultry products, there are also no mitigation measures to prevent this occurring.

APHA is working closely with environmental NGOs to manage the large wild bird mortality events, and mitigate the risk of exposure to humans, but again it is not possible to prevent access to wild mammals, or to decontaminate the environment.

Do environmental conditions in the UK support the natural vectors of disease?

Outcome

Yes.

Quality of evidence

Good.

The list of susceptible avian species for AIV is long and has increased with the global circulation of the AI A(H5N1) clade 2.3.4.4 viruses. These susceptible species include poultry (galliform and anseriform poultry), captive birds and wild birds. In the current season, HPAI A(H5N1) has been detected in 47 bird species at 311 locations across 77 counties in England, Scotland and Wales between October 2022 and March 2023. While the majority of species findings are in the Anatidae (swans, geese and ducks) and Charidriiform families (waders, gulls and auks) there are also raptors, passeriforms (songbirds and perching birds) and columbiforms (pigeons and doves), among others.

The surveillance of wild birds in the UK is not designed to give detailed monitoring of each and every possible infected bird. It is to inform disease risk assessments about the circulating viruses from one year to the next and hence is limited to target species and die-offs in new areas. The risk levels are assessed every week by experts and published on the avian Influenza information pages on GOV.UK. These risk levels are used to inform policy and operational decisions.

Historically, there has been limited routine disease surveillance for AIVs in non-avian species in the UK. However, incidental findings of AI A(H5N1) infecting mammals have been reported through retrospective testing of samples (37).

Will there be human exposure?

Outcome

No: general population.

Yes: for individuals interacting with infected non-avian species.

Quality of evidence

Satisfactory.

The general UK population is unlikely to be in close, prolonged, unprotected contact with AI A(H5N1) infected non-avian species.

Human infections of AI reported in the scientific literature have been attributed to close contact with infected poultry, wild birds or contaminated materials.

There have never been reports of AI transmitting from non-avian species to humans, or vice versa, in the UK. Unprotected contact with infected animals and/or contaminated tissues and fluids from an infected animal present the greatest risk of exposure to humans, particularly to those who have regular contact with non-avian UK species, such as volunteers or staff at rescue and rehabilitation centres, veterinarians and pathologists. For individuals interacting with wildlife as part of their work, the risk of exposure would be higher, although mitigated if appropriate PPE is worn.

Are humans highly susceptible?

Outcome

No.

Quality of evidence

Satisfactory.

Despite the high number of poultry outbreaks and likely human exposures to the virus at the human-animal environment interface, from 2020 to the end of December 2022, only 6 AI A(H5N1) clade 2.3.4.4b virus detections in humans were reported globally. Most of these cases reported no or mild symptoms except for a fatal case in China and a case in Vietnam recovering from severe disease (11). All these cases had exposure to infected poultry. Additionally, human-to-human transmission of AI A(H5N1) has never been reported.

There is a paucity of data relating to risk factors for increased susceptibility of humans to AI A(H5N1) clade 2.3.4.4b.

UKHSA works with APHA, Defra and the public health agencies of the 4 nations to investigate the risk to human health of AI A(H5N1) in the UK. Human exposures to AI are managed by local health protection teams (HPTs). Between 1 October 2022 and 4 July 2023, 2,577 exposures of humans to infected poultry, captive or wild birds were reported in England. During the 2022 to 2023 season, 4 human detections of AI A(H5N1), all in England, have been reported (38).

Transmission of AI A(H5N1) from non-avian species to humans has never been reported in the UK.

Outcome of probability assessment

The probability of human infection with AI A(H5N1) from non-avian UK species in the general population is considered Very Low.

For individuals interacting with infected non-avian species, the probability would be considered Low.

Question 5

Step 2: Assessment of the impact on human health

Good.

Avian influenza A(H5N1) is not considered endemic in the UK, and while outbreaks can occur at any point in the year, the UK typically experiences a seasonal increase of AI associated with incursions of infected wild migratory birds during the winter. Infected migratory birds can subsequently infect local and sedentary wild bird species, poultry, other captive birds and non-avian species in the UK. This can result in local transmission. Where infected birds are present, then transmission to other species, including mammals, may occur.

During the current AI transmission season (October 2022 to July 2023) there have been 1,436 findings in 58 wild bird species which have been found dead and tested positive for AI A(H5N1). Many of these findings have been in species which are usually considered sedentary or year-round residents rather than purely in migratory birds.

In addition, as of 25 July 2023, there have been 23 findings of A(H5N1) in otters, red foxes, harbour, common and grey seals, common dolphins and harbour porpoises out of over 170 wildlife samples collected over the last 2 years (37).

Is the UK human population susceptible?

Outcome

Yes/no.

Quality of evidence

Poor.

See above evidence.

Does it cause severe disease in humans?

Outcome

Yes/no. Disease severity is dependent on AI A(H5N1) lineage.

Unknown, high-risk individuals (immunocompromised, paediatric cases).

Quality of evidence

Poor.

Disease severity in humans infected with AI A(H5N1) varies depending on lineage. For example, Asian lineage AI A(H5N1) can cause severe disease in humans, with mortality rates of up to 50%. While this lineage does not easily infect people and has not acquired the ability to cause sustained transmission among humans (41), it is considered a public health concern. It is unclear whether AI A(H5N1) viruses in certain geographical regions differ in their pathogenicity. Clade 2.1 viruses (Indonesia) appear more pathogenic than clade 1 viruses (Cambodia/Thailand/Vietnam) and 2.3 viruses (China) (42).

Out of 6 Eurasian lineage AI A(H5N1) clade 2.3.4.4b human infections reported between January 2020 and December 2022, 4 cases presented with no or mild symptoms (1 case each in the UK and the US, and 2 cases in Spain) (11). The absence of symptoms in 2 poultry workers in Spain, together with the laboratory results which showed a very low viral load and the absence of specific H5 antibodies against the A/H5 virus, suggested that the positive results in the PCR were most likely due to environmental contamination, rather than legitimate infections (43). A fatality was reported in a case in China, while severe disease was reported in a case in Vietnam whom subsequently recovered. No information on comorbidities in these cases was available.

In January and March 2023, human cases of AI A(H5) were reported in Ecuador (12) and Chile (16,17), respectively. Both cases, neither of which had known comorbidities, required admission to intensive care units for medical treatment and mechanical ventilation. The latter case was subsequently confirmed as being infected with AI A(H5N1) clade 2.3.4.4b infection (17).

During 2023 (as of July), 4 asymptomatic human detections of AI A(H5N1) have been identified in England.

There is a paucity of evidence on what risk factors may increase disease severity and poorer clinical outcomes in human cases with AI A(H5N1) clade 2.3.4.4b infection.

Is it highly infectious to humans?

Outcome

No.

Quality of evidence

Satisfactory.

See above evidence.

Would a significant number of people be affected?

Outcome

No.

Quality of evidence

Satisfactory.

As of July 2023, there has been a single human case of AI A(H5) and 4 confirmed cases of AI A(H5N1) reported in the UK. The cases had exceptionally close contact with infected live poultry. Although people have been infected with AI A(H5N1) clade 2.3.4.4b globally, this is rare and subsequent human-to-human transmission has not been observed.

Within the UK, well established and robust public health interventions are implemented in response to a human becoming symptomatic following contact with known AIV infection (for example in poultry). This involves the isolation and treatment of a case, and extensive contact tracing designed at preventing further transmission.

Are effective interventions (preventative or therapeutic) available?

Outcome

Yes.

Quality of evidence

Satisfactory.

There are no control measures preventing the migration of infected wild birds into the UK. Additionally, disease surveillance, including of AIV, in non-avian wildlife in the UK is limited. National surveillance and control of AIV in poultry and surveillance in wild birds is conducted annually in Great Britain by the APHA on behalf of Defra, Welsh Government and Scottish Government and by DAERA in Northern Ireland.

In the UK, there are well established pathways for the prompt diagnosis and treatment of a human case of AIV (44). Cases may be given antiviral medicine such as oseltamivir (Tamiflu) or zanamivir (Relenza), which help reduce the severity of disease, prevent complications and improve the chances of survival (45). To date, there have been no documented incidents of AI A(H5N1) transmission from infected non-avian species to humans in the UK, and so such pathways have never been applied in this scenario.

Outcome of impact assessment

The impact of avian influenza A(H5N1) from non-avian species on human health in the UK is considered Very Low to Low.

Note: detailed risk assessments for individual AIV subtypes can be found at Avian influenza: guidance, data and analysis.

Question 6

Annexe A: Assessment of the probability of infection in the UK population algorithm

Accepted Answer

Question 7

Annexe B: Accessible text version of the probability of infection in the UK population algorithm

Accepted Answer

Outcomes are specified with (Outcome) beside the appropriate answer.

Question 1: Is this a recognised human disease?

Yes

Go to question 3. (Outcome)

No

Go to question 2. (Outcome)

Question 2: Is this a zoonosis or is there a zoonotic potential?

Yes

Go to question 4. (Outcome)

No

The probability of infection in the UK population is considered very low.

Question 3: Is this disease endemic in humans within the UK?

Yes*

Go to question 5.

No

No

The probability of infection in the UK population is considered low. (Outcome)

**Includes susceptibility to animal-derived variants

Question 10: Is the disease highly infectious in humans?

Yes

The probability of infection in the UK population is considered high.

No

The probability of infection in the UK population is considered moderate.

Question 8

Annexe C: Assessment of the impact of infection in the UK population algorithm

Accepted Answer

Question 9

Go to question 10.

No

No

The impact of infection in the UK population is considered very high.

Question 10

References

Accepted Answer

1. Health and Safety Executive. Working with highly pathogenic avian influenza virus. Accessed: 28 April 2023.

2. Defra and APHA. Influenza A(H5N1) infection in mammals: suspect case definition and diagnostic testing criteria. Accessed 28 April 2023. 2023.

3. Defra and APHA. Avian influenza and influenza of avian origin: diagnostic testing, controls and reporting obligations. Accessed 28 April 2023. 2023.

4. Mostafa A, Abdelwhab EM, Mettenleiter TC and others. Zoonotic Potential of Influenza A Viruses: A Comprehensive Overview. Viruses. 2018;10(9): 497.

5. Van Kerkhove MD, Mumford E, Mounts AW and others. Highly Pathogenic Avian Influenza (H5N1): Pathways of Exposure at the Animal‐Human Interface, a Systematic Review. PloS One. 2011; 6(1): e14582.

6. European Food Safety Authority. Avian influenza. Accessed 28 April 2023.

7. WHO. Avian influenza: assessing the pandemic threat. Accessed 28 April 2023. 2005.

8. Malik Peiris JS. Avian influenza viruses in humans. Revue scientifique et technique (International Office of Epizootics). 2009; 28(1): 161-173.

9. Food and Agriculture Organization of the United Nations. Global AIV with Zoonotic Potential: Situation update. Accessed 28 April 2023. 2023.

10. WHO. WHO Disease Outbreak News: Avian influenza A(H5N1) – Spain. Accessed 28 April 2023. 2022.

11. WHO. Assessment of risk associated with recent influenza A(H5N1) clade 2.3.4.4b viruses. Accessed 11 February 2023. 2022.

12. WHO. WHO Disease Outbreak News: Human infection caused by avian influenza A(H5) – Ecuador. Accessed 11 February 2023. 2023.

13. Alfredo B, Alfaro-Núñez A, de Mora D and others. First case of human infection with highly pathogenic H5 avian Influenza A virus in South America: A new zoonotic pandemic threat for 2023? Journal of Travel Medicine. 2023.

14. The Government of Hong Kong, Centre for Health Protection of the Department of Health. CHP closely monitors human case of avian influenza A(H5N1) in Mainland. Accessed 13 March 2023. 2023.

15. Center for Infectious Disease Research and Policy. China reports new H5N1 avian flu case. Accessed 13 March 2023. 2023.

16. Pan American Health Organization. Informative Note: Human infection caused by avian influenza A(H5) virus in Chile - 31 March 2023. Accessed 6 April 2023. 2023.

17. US Centers for Disease Control and Prevention. Human Infection with highly pathogenic avian influenza A(H5N1) virus in Chile. Accessed 18 April 2023. 2023.

18. Reperant LA, Rimmelzwaan GF and Kuiken T. Avian influenza viruses in mammals. Revue scientifique et technique (International Office of Epizootics). 2009; 28(1): 137-159.

19. Animal and Plant Health Inspection Service. 2022-2023 Detection of Highly Pathogenic Avian Influenza in Mammals. Accessed 11 February 2023. 2023.

20. WHO. Cumulative number of confirmed human cases of avian influenza A(H5N1) reported to WHO, 2003 to 2023. Accessed 11 February 2023. 2023.

21. Reperant LA, Osterhaus ADME and Kuiken T. Influenza in aquatic mammals. In: Gavier-Widen D, Meredith A, Duff JP, editors. Infectious diseases of wild animals and birds in Europe, Wiley-Blackwell Press. 2012; 53–55.

22. Fereidouni S, Munoz O, Von Dobschuetz S and others. Influenza Virus Infection of Marine Mammals. EcoHealth. 2016; 13(1): 161-170.

23. Runstadler JA and Puryear W. A Brief Introduction to Influenza A Virus in Marine Mammals. In: Spackman E, editor. Animal Influenza Virus: Methods and Protocols. New York, NY, Springer US 2020; 429-50.

24. Montserrat A, Isabella M, Azucena S and others. Highly pathogenic avian influenza A(H5N1) virus infection in farmed minks, Spain, October 2022. Eurosurveillance. 2023; 28(3): pii=2300001.

25. Gamarra-Toledo V, Plaza PI, Gutiérrez R and others. (Pre-print) Mass Mortality of Marine Mammals Associated to Highly Pathogenic Influenza Virus (H5N1) in South America. BioRxiv. 2023.

26. Leguia M, Garcia-Glaessner A, Muñoz-Saavedra B and others. (Pre-print) Highly pathogenic avian influenza A (H5N1) in marine mammals and seabirds in Peru. BioRxiv. 2023.

27. Alkie TN, Cox S, Embury-Hyatt C and others. Characterization of neurotropic HPAI H5N1 viruses with novel genome constellations and mammalian adaptive mutations in free-living mesocarnivores in Canada. Emerging Microbes & Infections. 2023; 12(1): 2186608. DOI: 10.1080/22221751.2023.2186608.

28. WHO. Influenza A (H5) - United Kingdom of Great Britain and Northern Ireland. Accessed 11 February 2023. 2022.

29. Hervé S, Schmitz A, Briand FX and others. Serological Evidence of Backyard Pig Exposure to Highly Pathogenic Avian Influenza H5N8 Virus during 2016-2017 Epizootic in France. Pathogens. 2021; 10(5): 621. DOI: 10.3390/pathogens10050621.

30. Meseko C, Globig A, Ijomanta J and others. Evidence of exposure of domestic pigs to Highly Pathogenic Avian Influenza H5N1 in Nigeria. Scientific Reports. 2018; (8): 5900.

31. Abdel-Moneim AS, Abdel-Ghany AE and Shany SA. Isolation and characterization of highly pathogenic avian influenza virus subtype H5N1 from donkeys. Journal of Biomedical Science. 2010; (17): 25.

32. US Centers for Disease Control and Prevention. Transmission of Avian Influenza A Viruses Between Animals and People. Accessed 22 February 2023. 2022.

33. Lipatov AS, Kwon YK, Sarmento LV and others. Domestic Pigs Have Low Susceptibility to H5N1 Highly Pathogenic Avian Influenza Viruses. PLOS Pathogens. 2008; 4(7): e1000102.

34. Romero Tejeda A, Aiello R, Salomoni A and others. Susceptibility to and transmission of H5N1 and H7N1 highly pathogenic avian influenza viruses in bank voles (Myodes glareolus). Veterinary Research. 2015; 46(1): 51. DOI: 10.1186/s13567-015-0184-1.

35. Root J, Shriner S. Avian Influenza A Virus Associations in Wild, Terrestrial Mammals: A Review of Potential Synanthropic Vectors to Poultry Facilities. Viruses. 2020; 12(12): 1352. DOI: 10.3390/v12121352.

36. Defra. Notifiable Avian Disease Control Strategy for Great Britain. Accessed 22 February 2023. 2019.

37. Defra and APHA. Bird flu (avian influenza): findings in non-avian wildlife: Confirmed findings of influenza of avian origin in non-avian wildlife. Accessed: 11 February 2023. 2023.

38. UK Health Security Agency. Investigation into the risk to human health of avian influenza (influenza A H5N1) in England: technical briefing 3. Accessed: 1 May 2023. 2023.

39. US Centers for Disease Control and Prevention. Past Examples of Probable Limited, Non-Sustained, Person-to-Person Spread of Avian Influenza A Viruses. Accessed: 11 February 2023. 2022.

40. US Centers for Disease Control and Prevention. Influenza Type A Viruses. Accessed: 11 February 2023. 2022.

41. Malik Peiris JS. Avian influenza viruses in humans. Revue scientifique et technique (International Office of Epizootics). 2009; 28(1): 161 to 173.

42. Writing Committee of the Second World Health Organization Consultation on Clinical Aspects of Human Infection with Avian Influenza A Virus. Update on avian influenza A (H5N1) virus infection in humans. New England Journal of Medicine. 2008; 358: 261 to 273.

43. Esteban A, Inmaculada C, Alejandro GP and others. Influenza A(H5N1) detection in two asymptomatic poultry farm workers in Spain, September to October 2022: suspected environmental contamination. Euro Surveillance. 2023; 28(8): pii=2300107.

44. UK Health Security Agency. Managing the human health risk of avian influenza in poultry and wild birds: Guidance for health protection teams. Accessed 1 May 2023. 2023.

45. National Health Service. Avian flu. Accessed 11 February 2023. 2022.

46. UKHSA. Avian flu detected in 2 individuals taking part in testing programme. Accessed 1 June 2023. 2023.

47. WHO. Avian Influenza A(H5N1) - United Kingdom of Great Britain and Northern Ireland. Accessed 1 June 2023. 2023.

48. Puryear W, Sawatzki K, Hill N and others. Highly Pathogenic Avian Influenza A(H5N1) Virus Outbreak in New England Seals, United States. Emerging Infectious Diseases. 2023; 29(4): 786-791.

Cookies on GOV.UK

About the Human Animal Infections and Risk Surveillance group

Version control

Summary

Assessment of the risk of infection in the UK

Probability

Impact

Level of confidence in assessment of risk

Actions and recommendations

Step 1. Assessment of the probability of infection in the UK human population

Is this a recognised human disease?

Outcome

Quality of evidence

Is this a zoonosis or is there zoonotic potential?

Outcome

Quality of evidence

Mammalian viral adaptation and changes to viral pathogenicity

Is the disease endemic in humans within the UK?

Outcome

Quality of evidence

Is the disease endemic in animals within the UK?

Outcome

Quality of evidence

Are there routes of introduction into animals in the UK?

Outcome

Quality of evidence

Figure 1. Exposure routes of AIV from infected wild birds and/or poultry to mammals and humans

Are effective control measures in place to mitigate against these routes of introduction?

Outcome

Quality of evidence

Do environmental conditions in the UK support the natural vectors of disease?

Outcome

Quality of evidence

Will there be human exposure?

Outcome

Quality of evidence

Are humans highly susceptible?

Outcome

Quality of evidence

Outcome of probability assessment

Step 2: Assessment of the impact on human health

Is there human-to-human spread of this pathogen?

Outcome

Quality of evidence

Is there zoonotic or vector borne spread of this pathogen?

Outcome

Quality of evidence

For zoonoses or vector-borne disease is the animal host or vector present in the UK?

Outcome

Quality of evidence

Is the UK human population susceptible?

Outcome

Quality of evidence

Does it cause severe disease in humans?

Outcome

Quality of evidence

Is it highly infectious to humans?

Outcome

Quality of evidence

Would a significant number of people be affected?

Outcome

Quality of evidence

Are effective interventions (preventative or therapeutic) available?

Outcome

Quality of evidence

Outcome of impact assessment

Annexe A: Assessment of the probability of infection in the UK population algorithm

Annexe B: Accessible text version of the probability of infection in the UK population algorithm

Question 1: Is this a recognised human disease?

Yes

No

Question 2: Is this a zoonosis or is there a zoonotic potential?

Yes

No

Question 3: Is this disease endemic in humans within the UK?

Yes*

No

Question 4: Is this disease endemic in animals in the UK?

Yes

No