Influenza of avian origin in UK seal populations: qualitative assessment of the risk to the UK human population

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
Health and Safety Executive, Republic of Ireland
Infrastructure, Housing and Environment, Government of Jersey
Isle of Man Government
States Veterinary Officer, Bailiwick of Guernsey

Information on the risk assessment processes used by the HAIRS group can be found at HAIRS risk assessment process.

Question 2

Version control

Accepted Answer

Date of this assessment: June 2022

Version: 1.0

Reason for the assessment: Increased reports of influenza A viruses of avian origin infecting mammals; concerns for mammalian adaptation of these viruses.

Completed by: HAIRS members

Non-HAIRS group experts consulted: Ian Brown (APHA), Cat Man (APHA), James Barnett (Cornwall Marine Pathology Team), Johanna Baily (University of Stirling), Lara Turtle (Defra), Gavin Dabrera (UKHSA)

Date of initial risk assessment: N/A

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

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 avian influenza viruses (AIV), and a variety of influenza subtypes 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. AIV have long been recognised in Europe, where there is longstanding annual surveillance for poultry and wild bird infections. Whilst there is no routine surveillance for diseases including AIV specifically in marine mammals in the UK, sporadic findings of AIV infecting seals have been reported. These include subtypes A(H3N8) isolated from a juvenile grey seal (Haliochoerus grypus) in 2017, and A(H5N8) from a grey seal and 2 common seals (or harbour seal (Phoca vitulina)) in 2020. Although the UK is home to 38% of the entire world’s population of grey seals, and 30% of the European subspecies of common seals, there have never been reports of AIV transmitting from seals to humans, or vice versa, in the UK.

Assessment of the risk of infection in the UK

Probability

General population: very low.

The probability of infection would be considered low for those working with infected seals.

Impact

Very low to low.

Level of confidence in assessment of risk

Poor/Satisfactory.

AIV outbreaks in seal populations have occurred sporadically over time. Due to the absence of routine disease surveillance in UK seal populations, the true extent of AIV infections in seal populations cannot be determined. There is a paucity of evidence on the susceptibility of humans to AIV’s infecting seals, and only 2 documented incidents of AIV transmission from seals to humans, both resulting in mild disease in human cases. Several questions relating to the viral ecology and adaptation to marine mammal hosts exist. Other evidence gaps include:

How does viral genetic diversity, particularly in recovering seal populations or subpopulations, impact disease maintenance and viral circulation?
Are small host populations more highly impacted by disease events, even in the absence of high mortality?
Do genetic differences between marine mammal hosts (for example seal species) impact the ecological role of those hosts in virus maintenance and circulation?
Do marine mammal-adapted viruses share molecular signatures of other mammalian adapted viruses?

Actions and recommendations

During April 2021, an information campaign was launched by the Seal Alliance and Defra to educate the public on keeping their distance from seals to protect human and seal health. The general public are advised against approaching and interacting with seals in the UK, even when the animals are in danger or distress.

If a member of the public observes a seal 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 seals as part of their work should consider utilising appropriate personal protective equipment (PPE) including aerosol-related respiratory precautions, and seal-specific precautions such as thick gloves and wooden boards or barriers if direct contact with a seal is necessary (for example during a seal rescue), to avoid animal bites and reduce the exposure to potential zoonotic infections.

The APHA wildlife expert group maintains close interactions with non-governmental organisations (NGOs) including marine wildlife organisations and rescue centres. Where appropriate, NGOs should be encouraged to collect and submit samples from sick or dead seals to APHA Weybridge diagnostic laboratories for testing, of which AIV should be a considered differential, so to be alerted to changes in viral epidemiology and potential risk.

A review of seal health surveillance across the UK is recommended, with the long-term aim to establish routine disease surveillance in marine mammals in the UK.

Please note: this risk assessment provides an ecological perspective on AIV in seal populations globally and reviews the probability of AI exposure from infected seals to humans in the UK. The statement provides reference to multiple AIV subtypes that have been reported to infect marine mammals, including seals. It does not assess, in detail, the risk of individual AIV subtypes to human health, but more so on the potential transmission pathway of AIV from seals to humans. Existing risk assessments for specific AIV subtypes can be found at Avian influenza: guidance, data and analysis.

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 found at Annexe A.

Is this a recognised human disease?

Outcome

Yes/no.

Quality of evidence

Poor.

Note

As there are only 2 documented incidents involving AI transmission from seals to humans globally, which resulted in mild disease in the human cases, the quality of evidence in relation to human disease following contact with an infected seal is poor. This question is therefore answered in the context of AIV from other sources, notably birds.

AIV 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 (1). Although AIVs do not usually infect people, rare cases of human infection do occur 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 (2).

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), indicating the severity of disease caused in galliform poultry hosts (3). 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%. Whilst these subtypes do not easily infect people and have not acquired the ability to cause sustained transmission among humans (4), they are considered subtypes of public health concern.

Is this a zoonosis or is there zoonotic potential?

Outcome

Yes.

Quality of evidence

AIV from seals: poor.

AIV from birds: satisfactory.

Note

As there are only 2 documented incidents involving AI transmission from seals to humans globally, which resulted in mild disease in the human cases, the quality of evidence in relation to transmission to humans following contact with an infected seal is poor. This question is therefore answered in the context of AIV from other sources, notably birds.

HPAI viruses, particularly A(H5) subtypes, are remarkable because of their expanding non-avian host range (5). For example, AI A(H5N1) has caused severe and sometimes fatal disease in several naturally infected species (for example big cats, pigs and humans). Where AI A(H5) subtypes circulate in poultry, then sporadic human cases should not be unexpected in people with close contact or high levels of exposure. This is particularly evident for the Asian lineage subtype A(H5N1), with 864 human cases being reported from 18 counties between January 2003 and December 2021 (6). Human cases of AI A(H5N6) are also being more frequently reported. In China, for example, 21 laboratory confirmed human cases have been reported between January to May 2022 (7), with most cases being exposed to live poultry prior to symptom onset. In April 2022, China reported the first human infection with AI A(H3N8), in a child who had exposure to domestic poultry prior to symptom onset (8). A second, unrelated human case of AI A(H3N8) infection was reported in China during May 2022 (9).

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 domestically kept birds which 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 (10). The human case remained clinically asymptomatic and no subsequent human-to-human transmission was detected.

In February 2021, Russia reported the first human infections of AI A(H5N8) (11). Phylogenetic analysis of viral isolates from these cases indicated that the strain was genetically similar to AI A(H5N8) that had been circulating in wild and domestic birds in the Eurasian region since July 2020 (12), and possessed several molecular markers associated with mammalian adaption (13). Phylogenetic and whole genome sequencing analysis of the human virus at the protein level revealed critical mutations in proteins which contribute to increased virulence and avian-to-human adaptation (14). Whilst these human cases were asymptomatic and there was no clinical evidence of onward transmission, this incident reaffirmed the zoonotic potential of this subtype, which, along with other subtypes, may become more adapted to non-avian hosts over time (11).

Mammalian viral adaptation and changes to viral pathogenicity

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 (5). Following increased awareness for potential spread of influenza A subtypes of avian origin 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; the latter being of interest due to the detection of numerous subtypes found infecting both cetaceans (H1N3, H13N2, H13N9) and pinnipeds (H7N7, H4N5, H4N6, H3N3, H1N1, H3N8, H10N7, H5N8) (15).

AI transmission from avian to mammalian species, may play an important role in the evolution of new mammalian viral strains (16). After 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 (17). For example, the pathogenicity of AI A(H7N7) isolated from seals increased in mammalian species such as mice, ferrets and rats, but only after several passages of the virus in chicken embryo cells (18). These findings suggest a loss in viral pathogenicity following adaptation to mammals, which could only be regained via passage through a poultry host. Whilst AI A(H7N7) found in dead seals was genetically similar to other AI viral strains, it behaved biologically more like a mammalian strain, replicating to high titres in ferrets, cats and pigs (19). By contrast, it replicated poorly and produced no clinical signs in avian species (chickens, ducks, turkeys and parakeets) and faecal shedding in these animals after experimental infection was not detected. This was probably due to its adaptation to mammalian hosts during replication in seals (19). The exact mechanism involved in viral transmission from bird to seal remains unclear. Moderate attachment of AIV to the cell receptors in the trachea and bronchi of common and grey seals suggests high susceptibility to these viruses within these species (20).

Influenza virus transmission between humans and seals

There are limited reports of influenza transmission between humans and seals. In 2010, whole genome sequencing of influenza A(H1N1) from healthy Northern elephant seals revealed greater than 99% homology with A/California/04/2009 (H1N1) (pH1N1) that emerged in humans from swine in 2009 (21). This was the first report of pH1N1 (A/Elephant seal/California/1/2010) in any marine mammal and provided evidence for cross species transmission of influenza A virus to free-ranging wildlife from humans (21).

There have been only 2 documented incidents of AIV transmission from seals to humans. During the 1979 to 1980 AI A(H7N7) outbreak in common seals in the northeast of the US, purulent conjunctivitis was observed in 4 people who had been involved in autopsies of dead seals, but no virus isolation was attempted in that period (22). However, during subsequent experimental infections of common seals using the identical virus, an infected animal sneezed on an investigator’s face, who then developed severe conjunctivitis. Two days post infection, AI A(H7N7) was isolated from a swab sample of the patient’s conjunctival membrane. The authors reported the virus as being antigenically very close to A/FPV/Dutch/27 (H7N7), which had been responsible for a case of human influenza virus infection following an accidental laboratory exposure in 1977. AI A(H7N7) infecting the seals proved to have the potential to cause conjunctivitis in humans but not sustained human-to-human transmission. The affected people reported in these studies recovered without complications, and antibodies to the virus were not detectable in the serum of infected individuals.

Is the disease endemic in the UK?

Outcome

No.

Quality of evidence

AIV in seals: poor.

AIV in birds: satisfactory.

AI is not considered endemic in the UK, and whilst 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 seals) and infected seabirds at hauling-out sites or when feeding on a common food source may result in cross-species AIV transmission (17).

Sporadic findings of AI in seals have been reported in the UK. These include subtypes A(H3N8) isolated from a juvenile grey seal (Halichoerus grypus) in Cornwall during 2017 (23), and A(H5N8) from a grey seal and 2 common seals (or harbour seal (Phoca vitulina)) in Norfolk during 2020 (24). Due to the absence of routine disease surveillance in UK marine mammalian populations, it cannot be determined if AIV in these species is incidental, or if AIV’s exhibit endemicity in UK seal populations.

Characteristics of epizootics of influenza among seal populations (global)

Influenza A infection has been detected in marine mammals dating back to 1975, with additional unconfirmed outbreaks as far back as 1931. Over the past forty years, infectious virus has been recovered on approximately 10 separate occasions from both pinnipeds (common seal, Northern elephant seal (Mirounga angustirostris), and Caspian seal (Pusa caspica)) and cetaceans (Striped dolphin (Stenella coeruleoalba) and long-finned pilot whale (Globicephala melaena)). Recovered viruses have spanned a range of subtypes (H1, H3, H4, H7, H10, and H13) (17) and, in all but A(H1N1), show strong evidence for deriving directly from avian sources. To date, there have been 5 unusual mortality events in seals directly attributed to influenza A viruses; these have primarily occurred in common seals in the North-eastern United States and in the North Sea. In July 2022, the US Department of Agriculture’s Animal and Plant Health Inspection Service’s National Veterinary Services Laboratories confirmed that samples from 4 stranded seals in Maine, US, tested positive for Highly Pathogenic AI A(H5N1) (25). No associated human infections were reported during these incidents.

Are there routes of introduction into 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. Infected migratory birds can subsequently infect local and sedentary wild bird species, poultry or other captive birds.

Influenza A viruses in marine mammals with linked avian origin

The current knowledge of AI infecting marine mammals, including antigenic and phylogenetic analyses of isolated viruses, suggests that transmission from wild birds is the most probable route of AI introductions into marine mammal populations (26 to 29). For example, phylogenetic analysis of 3 AI subtypes including A(H1N3) and A(H13N2) from whales, and A(H7N7) from seals revealed high genetic relatedness to isolates from gulls and terns (30), with introductions of AI from wild birds into marine mammal populations likely occurring on multiple, independent occasions (17). This suggested that whilst viruses can transmit to mammalian populations, the mammals are unlikely to act as reservoir hosts and sustain endemic infection.

Several studies have highlighted the ability of AIV to infect seal species. For example, AI A(H5N8) was isolated from lung samples of 2 grey seals stranded on the Baltic coast of Poland in 2016 and 2017. The clade was closely related to A(H5N8) circulating in European avian species at the time (31). In December 2020, A(H5N8) nucleic acid was detected following post-mortem in brain and lung tissues of a grey seal and 2 common seals that had recently died at a wildlife rehabilitation centre in the UK. Genetic sequencing revealed a 99.9% similarity to A(H5N8) detected in mute swans (Cygnus olor) that were also housed at the centre and had died (24). In mid-August 2021, tracheal swabs and tissue samples obtained from 3 adult harbour seals found on the German North Sea coast were investigated for the presence of morbilliviruses, herpesviruses, and AI as part of regular health monitoring. All 3 harbour seals belonged to the same population of approximately 8,850 individuals in the Wadden Sea of Schleswig-Holstein. High viral loads of A(H5N8) were detected in brain tissue of the 3 seals. Whole genome sequencing revealed 2 genotypes; one similar to the HPAI A(H5N8), that dominated the 2020/2021 avian epizootic in Germany, and the other similar to Eurasian LPAI strains found in wild birds and poultry holdings in Germany during the past years. Further analysis revealed the presence of the E627K mutation in the genome, indicating that replication of avian viruses in seals may allow HPAI to acquire mutations needed to adapt to mammalian hosts (32, 33).

In September 2021, the Danish Veterinary Consortium detected A(H5N8) in a deceased harbour seal found on a beach in Southwest Funen. The seal was emaciated with pronounced skin changes on large parts of the body. AIV was detected in the lung, but otherwise no other disease-causing organisms could be detected that could provide an explanation for the seal’s death. The Centre for Diagnostics examined 29 harbour seals and 15 grey seals in 2021; with only one testing positive for AIV. The detected virus was closely related to those circulating in wild birds and domestic poultry in Denmark and the rest of Europe during the Autumn of 2020 (34).

The most notable event associated with AI in seals occurred in 2014, where increased mortality was reported among common seals along the coasts of Sweden and Denmark, associated with AI A(H10N7) infection (35 to 37). Subsequent spread of the virus to seals along the coast of Germany resulted in between 1,500 and 2,000 seal deaths (36). The virus was also detected in dead seals along the coast of the Netherlands between November 2014 and January 2015. Mass mortality suggested rapid seal-to-seal transmission during these outbreaks, and that seals may act as short-term intermediate hosts following a spill-over event that facilitates transmission within and possibly between species. In the wild, contact between marine mammals and bird species at hauling-out sites, or when feeding on the same food resources (for example fish or krill species), may facilitate cross-species transmission of AIV (17).

The risk of influenza epizootics spreading from northern European seal populations to UK seal populations

Yes: for individuals interacting with infected seals.

Quality of evidence

Satisfactory.

The general population is unlikely to be exposed to an infected seal. Although the magnitude of human-seal interaction in the UK is unknown, interactions between the general public and seals on beaches or whilst participating in recreational activities near seal habitats (for example water sports) would likely be transient in nature. However, disturbances to seals by humans is a significant and growing problem in the UK. Such interactions could result in physical injury to a member of the public, for example being bitten by a seal, and exposure to other zoonoses being harboured by an infected animal.

Human infections of AI reported in the scientific literature have predominantly been attributed to close contact with infected poultry, wild birds or contaminated materials. As described above, there have been only 2 reported incidents of AI transmission from seals to humans (22). Both incidents involved AI A(H7N7), and the 5 human cases developed conjunctivitis with no further complications. No sustained human-to-human transmission was observed (17).

There have never been reports of AI transmitting from seals to humans, or vice versa, in the UK. Unprotected contact with infected seals and/or contaminated tissues and fluids from an infected seal present the greatest risk of exposure to humans; particularly to those who have regular contact with seals, such as volunteers or staff at rescue and rehabilitation centres, veterinarians treating sick seals, and seal pathologists. For individuals interacting with seals as part of their work, the risk of exposure would be higher, although mitigated if appropriate PPE is worn (see Action(s) and/or recommendations at the beginning of this assessment).

Note

Whilst the zoonotic risk may be greater from a symptomatic seal to a human, zoonotic disease transmission from asymptomatic animals should not be excluded, and individuals handling apparently ‘healthy’ animals should take appropriate precautions.

Are humans highly susceptible?

Outcome

No.

Quality of evidence

AIV from seals: poor.

AIV from birds: satisfactory.

Whilst there are many different AIV subtypes (42), most have never been observed to infect humans. Although the number of human infections with specific subtypes of AIV has increased in recent years (for example AI A(H5N6) cases in China), human cases remain rare. There are 4 subtypes of greatest public health concern, all Asian lineage:

A(H5N1) (since 1997)
A(H7N9) (since 2013)
A(H5N6) (since 2014)
A(H5N8) (since 2016)

Human infections with AIV are usually the result of close, prolonged and unprotected (for example absence of PPE) contact with infected birds or environments contaminated by an infected bird’s saliva, mucous or faeces. Although people have been infected with AIV, subsequent human-to-human transmission is very rarely observed (see (43)).

There is a paucity of evidence on the susceptibility of humans to AIV’s infecting seals.

Outcome of probability assessment

The probability of human infection with AIV from seals in the general UK population is considered very low.

For individuals interacting with infected seals, the probability would be considered low.

Question 5

Step 2: Assessment of the impact on human health

Accepted Answer

The scale of harm caused by the infectious threat in terms of morbidity and mortality: this depends on spread, severity, availability of interventions and context. Please read in conjunction with the Impact Algorithm found at Annexe C.

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

Outcome

The UK is home to 38% of the entire world’s population of grey seals, and 30% of the European subspecies of common seals. In the UK, there have been sporadic and incidental findings of AIV infecting seals. This includes the isolation of AI A(H3N8) from a seal pup in Cornwall in 2017 (23), and AI A(H5N8) from grey and common seals at a wildlife rehabilitation centre on the Norfolk coast in 2020 (24).

Is the UK human population susceptible?

Outcome

See above evidence.

Are effective interventions (preventative or therapeutic) available?

Outcome

Yes.

Quality of evidence

Satisfactory.

There are no control measures preventing the migration of infected seals or wild birds into the UK. Additionally, disease surveillance, including of AIV, in marine mammal hosts in the UK is limited. National surveillance and control of AIV in poultry and wild birds is conducted annually by UK Governments Defra and APHA. The UKHSA works closely with Defra and APHA during AI incidents where there are human exposures to infected birds (see (40)).

In the UK, there are well established pathways for the prompt diagnosis and treatment of a human case of AIV (40). 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 (42). To date, there have been no documented incidents of AIV transmission from an infected seal to a human in the UK, and so such pathways have never been applied in this scenario.

Outcome of impact assessment

The impact of AIV from seals 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

The probability of infection in the general UK population is high

No

The probability of infection in the general UK population is moderate

Question 8

Annexe C: Assessment of the impact on human health algorithm

Accepted Answer

Question 9

The impact on human health in the UK is high

No

The impact on human health in the UK is very high

Question 10

References

Accepted Answer

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About the Human Animal Infections and Risk Surveillance group

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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

Note

Is this a zoonosis or is there zoonotic potential?

Outcome

Quality of evidence

Note

Mammalian viral adaptation and changes to viral pathogenicity

Influenza virus transmission between humans and seals

Is the disease endemic in the UK?

Outcome

Quality of evidence

Characteristics of epizootics of influenza among seal populations (global)

Are there routes of introduction into the UK?

Outcome

Quality of evidence

Influenza A viruses in marine mammals with linked avian origin

The risk of influenza epizootics spreading from northern European seal populations to UK seal populations

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 reservoirs or vectors of disease?

Outcome

Quality of evidence

Will there be human exposure?

Outcome

Quality of evidence

Note

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

Note

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

Would a significant number of people be affected?

Outcome

Quality of evidence

Is it highly infectious to humans?

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 assessment 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 zoonotic potential

Yes

No

Question 3: Is this disease endemic in the UK?

Yes