Research and analysis

SARS-CoV-2 in UK cervid populations: risk to humans

Published 9 March 2023

Animal Health, Food Safety and Public Health risk assessments for SARS-CoV-2 in UK cervids: executive summary

1. In August 2021, the US Department of Agriculture’s National Veterinary Services Laboratories reported infection of white-tailed deer (WTD, Odocoileus virginianus) with SARS-CoV-2. The Science Advisory Group for Emergencies (SAGE) commissioned a risk assessment from the Human Animal Infections and Risk Surveillance (HAIRS) group to look at the risk to public health from SARS-CoV-2 infected cervids in the UK. The same approach was taken as for a previous assessment of Chronic Wasting Disease in the UK cervid population, to account for the potential spread between animal species, through contact to humans and through consumption to humans.

2. The risk assessment processes for the different agencies follow different international standards and cannot easily be combined. Thus, 3 separate documents have been produced and this executive summary aims to give an overall conclusion.

3. The hazard was identified as any strain of SARS-CoV-2. Both the Delta and Omicron variants were detected in WTD and the related mule deer (Odocoileus hemionus). The herd seropositivity can reach significant levels of up to 40% in some cases, and experimental data have confirmed the spread between infected and naïve animals. There is one potential case of spill-back to a human (now reported in a peer reviewed paper). The route of introduction to deer is indirect contact with human cases, through contaminated feed, wastewater or possibly, but less likely, direct contact when humans are handling animals.

4. From an animal health perspective, the risk assessment considered the UK deer species to be susceptible, based on immunohistochemistry of binding sites. The management and ecology of the UK deer populations make them less likely to come into contact with humans than the US and Canada WTD populations. Nevertheless, there are several pathways for introduction of disease into the UK deer population, and subsequent exposure to and spread within UK cervids and other livestock is plausible, given SARS-CoV-2 is widely circulating in the UK human population. The conclusion was that for cervids, there is a very low to low risk of the disease being introduced to the UK (depending on the pathway), a plausible risk of spread to other cervids and a very low risk of spread to other livestock species. Surveillance undertaken through a wildlife research programme at the Animal and Plant Health Agency (APHA) has detected just a single seropositive fallow deer (Dama dama) out of many tens of samples, but the source of infection and the transmission pathways are not known at present. Fallow deer are kept in UK parks and collections, often farmed for venison production and are commonly observed in rural and green belt areas.

5. From a food safety perspective, consumption of venison in the UK mainly consists of UK origin cervid meat. There is no evidence to suggest SARS-CoV-2 is spread through consumption of infected livestock. The human-to-human transmission pathway is by far the greater risk to the human population. While there are differences in the way that cervid carcases are handled and meat is produced, in comparison to other ruminants (not removing spinal cords or ‘specified risk material’), nevertheless, the overall risk assessment considered there was a negligible risk to public health considering the lack of evidence for consumption being a major route of infection for humans.

6. From a public health (occupational exposure or non-food exposure) perspective, the risk assessment also assumes disease is already present in the UK and is circulating widely in humans, with this being the major pathway for further human cases to occur. The populations at risk are those in direct contact with infected cervids (for example game keepers, hunters, vets, knackermen, renderers and butchers), people taking dietary supplements, such as antler velvet, people in contact with pet animals which have consumed infected meat and environmental exposure. The overall risk was considered very low.

7. Therefore, the overall risk level in terms of deer infection with SARS-CoV-2 impacting on human SARS-CoV-2 prevalence is currently negligible, given the unlikely scenario of disease already being present in the UK cervid population, the presumed species barrier for transmission to other livestock, and the widespread human infection already present.

8. Nevertheless, there are substantial levels of uncertainty in terms of the level of infection in the UK in the future, the incubation period and infectious dose and the impact of mutation on future establishment of a reservoir species. There is a general concern that a wildlife reservoir could result in the appearance of new strains which may evade the vaccine-induced immune response in the human population. Therefore, these risk assessments will remain living documents and will be reviewed as new evidence becomes available.

Figure 1. Conceptual pathway for the risk assessments

Risk of SARS-CoV-2 to human health through non-food exposures to deer in the UK: qualitative assessment

About the Human Animal Infections and Risk Surveillance (HAIRS) group

This document was prepared by the UK Health Security Agency (UKHSA) on behalf of the joint 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)
• 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.

Version control

Date of this assessment

December 2022

Version

1.0

Reason for the assessment

Reports of human-to-deer transmission of SARS-CoV-2 and sustained transmission in white-tailed deer populations in North America. This assessment considers non-food borne risks of SARS-CoV-2 transmission to humans if the virus was present in UK deer populations.

Completed by

Dominic Mellor (Public Health Scotland) and HAIRS members

Non-HAIRS group experts consulted

Katherine Adam (Public Health Scotland)

Summary

The recent detection of SARS-CoV-2 in white-tailed deer (WTD, Odocoileus virginianus) in North America raises concerns about domestic exposure to SARS-CoV-2 in cervid populations within the UK and the risks to human health.

This assessment considers non-food exposure pathways in the UK.

The risk of exposure to SARS-CoV-2 through non-food routes in the UK is dependent on the level of the infection within UK deer species.

Surveillance undertaken through a wildlife research programme by APHA has detected just a single SARS-CoV-2 seropositive fallow deer (Dama dama) in the UK, out of many tens of samples processed. The source of infection and the transmission pathways is currently not known. Data to determine SARS-CoV-2 prevalence in UK cervid populations are not available. It remains necessary to accumulate evidence to determine our confidence in the absence of this disease within UK cervid populations.

This risk assessment assumes a pessimistic scenario where SARS-CoV-2 becomes present in UK deer populations.

This assessment is one of 3 parts. The other parts consider:

• qualitative assessment of the risk of SARS-CoV-2 being introduced into the cervid population in Great Britain – led by Defra
• qualitative assessment of the risk of SARS-CoV-2 to human health through food exposures to deer in the UK – led by the Food Standards Agency

Assessment of the risk of infection to the human population in the UK

Probability

Negligible if SARS-CoV-2 is not present in UK deer populations.

If SARS-CoV-2 is present in UK deer populations

• general population: the probability of infection would be very low (accounting for uncertainties in the scientific understanding of the virus in these species and its transmission potential)
• occupational exposures: the probability of infection would be considered moderate to high for individuals interacting with SARS-CoV-2 infected deer and their contaminated environments

Impact

Very low to low

Level of confidence in assessment of risk

Low. This is because there is no current evidence of SARS-CoV-2 infection in UK deer populations.

Further evidence is required to determine whether:

• sustained SARS-CoV-2 transmission can occur within UK deer populations, or the potential for new mutations or variants to arise in UK deer populations with the potential to transmit to humans
• and to what extent, human-to-deer transmission of SARS-CoV-2 is occurring in UK deer species

Action(s) and/or recommendations

For individuals that may have an occupational exposure to SARS-CoV-2 infected deer (such as deer farmers, slaughterhouse workers, wildlife rehabilitation workers, veterinarians or hunters), consideration should be given to the appropriate use of personal protective equipment to mitigate against the risk of SARS-CoV-2 exposure.

Epidemiology of SARS-CoV-2 in deer

Although SARS-CoV-2 (the virus that causes coronavirus (COVID-19)) is likely to have originated from an animal source, the ongoing pandemic is being sustained through human-to-human transmission. The primary route for exposure of humans to SARS-CoV-2 is via other infected humans. However, spill-over of the virus from humans to animals has been documented.

There have been several reports of SARS-CoV-2 detections by polymerase chain reaction (PCR) and subsequent serology in companion animals (mostly cats and dogs but also ferrets) in several countries, in a limited number of zoo animals and on mink farms (APHA collated data, World Health Organization for Animal Health Events in Animals). The majority of these reports suggest infected humans as the source of infection, or at least the source of the index case prior to sustained transmission between animals observed in some animal production facilities (for example mink farms). For further information on the susceptibility of animals to SARS-CoV-2 see Defra’s Qualitative assessment of the risk of SARS-CoV-2 being introduced into the cervid population in Great Britain.

In August 2021, the United States Department of Agriculture’s National Veterinary Services Laboratories announced confirmation of SARS-CoV-2 in wild WTD from Ohio (1). In addition, antibodies to SARS-CoV-2 were detected in 40% (152 out of 385) of wild WTD sampled from 4 US states (Illinois, Michigan, New York, and Pennsylvania) between January to March 2021 (2). Two experimental studies have also found that WTD inoculated with SARS-CoV-2 became infected, shed viable virus, transmitted infection to other WTD and developed SARS-CoV-2 antibodies. Infected WTD showed minimal clinical signs and/or pathological changes (3, 4).

Subsequent research detected SARS-CoV-2 virus by real-time reverse transcription PCR in more than one-third (129 out of 360, 35.8%) of nasal swabs obtained from wild WTD in north-east Ohio (US) during January to March 2021. Whole genome sequencing revealed viral isolates from infected deer represented strains dominant in the local human populations at the time. Possible deer-to-deer transmission of some of these viruses was also indicated. No spill-back into human populations was observed.

An observational surveillance study conducted in Ontario, Canada, during November and December 2021 identified a highly divergent lineage of SARS-CoV-2 in wild WTD. Analyses of deer-derived viral genomes provided evidence for evolution and transmission in deer and shared ancestry with mink-derived virus. The analyses also revealed an epidemiologically linked human infection. Thus, the study provided evidence for sustained evolution of SARS-CoV-2 in WTD and of deer-to-human transmission (5).

Distribution of SARS-COV-2 infectivity in deer tissues

Experimental infection studies in WTD have shown evidence of widespread tissue distribution of SARS-CoV-2 (3, 4). It is unknown whether this is generalisable to other deer species and natural infection.

SARS-CoV-2 infectivity in the environment

Currently, there is a paucity of evidence about the amount of live viable virus present in deer environments or the duration of viral survival in the environment and on fomites in the vicinity of deer. From studies published on WTD in North America, there is speculation that deer may experience high levels of viraemia and shedding that may be conducive to environmental transmission (6). It remains uncertain whether deer can experience clinical disease and whether clinical signs such as sneezing or nasal discharge increase the risk of transmission. Two previous experimental studies reported only subclinical infections in WTD challenged with SARS-CoV-2, but these were very small sample sizes (3, 4).

Surveillance and detection of human SARS-CoV-2 (including novel variants)

Surveillance for SARS-CoV-2 infection in humans in the UK has been extensive, with widespread availability lateral-flow self-testing kits, backed up by PCR testing. Extensive whole genome sequencing of viral isolates from PCR positive patients is carried out, which monitors the evolution of circulating viruses and identifies emerging variants and mutations. This surveillance is likely to identify new human cases, but it would not be able to distinguish isolates as being of cervid origin without mechanisms to carry out complementary surveillance in deer.

Although SARS-CoV-2 is currently endemic in the UK human population, there is a paucity of evidence to suggest that it is present in either wild or captive populations of deer. Surveillance undertaken through a wildlife research programme by the APHA has detected just a single SARS-CoV-2 seropositive fallow deer (Dama dama), out of many tens of samples processed. The source of infection and the transmission pathways is currently not known. This risk assessment therefore assumes a pessimistic scenario where SARS-CoV-2 becomes present in UK deer populations, and the possible routes of exposure for the UK human population.

Non-food routes of exposure to SARS-CoV-2 in UK deer

Appendix 1 illustrates pathways through which individuals interacting with deer in the UK could come into direct contact with SARS-CoV-2 infected tissues of deer.

Occupations with repeated contact with infected animals and direct handling of SARS-CoV-2 infected or potentially infected tissues would have a higher risk of exposure than the general public.

Non-food routes of human exposure to SARS-CoV-2 infectivity from UK deer include:

• direct contact with infected tissues of deer
• direct contact with live deer
• indirect exposure through other species that have consumed infected deer tissues
• indirect exposure through contact with contaminated environments

Direct contact with infected tissues of deer

There are several occupations which could involve handling SARS-CoV-2 infected animals, their carcasses or tissues and thus increasing SARS-CoV-2 exposure risk. These include:

• abattoir staff and slaughterhouse workers
• farmers
• veterinary surgeons
• Veterinary Investigation Centre staff
• hauliers
• knackery staff
• boning plant operators
• renderers
• butchers
• workers in zoos and circuses
• workers handling meat and bone meal
• incinerator operators
• landfill site workers
• cleaning and waste disposal workers
• maintenance engineers (for example in abattoirs, rendering plants, incinerators)
• taxidermists
• individuals handling injured deer or carcases following vehicle collisions
• gamekeepers
• conservationists and wildlife researchers
• hunters
• wildlife sanctuary and rehabilitation workers

Occupational exposures would likely occur through inoculation or introduction of contamination in the following ways:

• splashing into mucous membranes (eyes and mouth);
• inhalation;
• cuts, needle stick injury (7)

Hunters

Hunters are a group considered at greater risk of exposure in endemic areas of the US and Canada and would be subject to similar risks of exposure if SARS-CoV-2 were to become established in UK deer. They may be repeatedly exposed through direct handling of carcases while gralloching or field dressing, undertaking butchery most likely through handling and removing the head, respiratory and gastrointestinal tracts.

Deer vehicle collisions

Several thousand deer vehicle collisions occur in the UK each year (8). There is the potential for direct exposure to infected tissues of injured animals or carcases by members of the public and those dealing with and removing injured or dead deer.

Laboratory and Veterinary Investigation Centre staff working in diagnostic and research facilities

These staff may be regularly exposed to the highest infectivity tissues through diagnostic testing and research work, although research with, and testing of, deer tissues in the UK is likely to be limited.

Indirect exposure through other species that have consumed infected deer tissues

Risks to wildlife handlers or rehabilitators: there is a theoretical risk that wild carnivores and scavengers that have been feeding on deer carcasses could act as vehicles of infection from deer to humans involved in working with wildlife, particularly Mustelidae which are known to be susceptible to SARS-CoV-2 infection.

Risks to pet owners: there is the potential for deer meat and deer tissues to be incorporated into raw meat pet food products, which are then fed to pets in the UK, and may transfer SARS-CoV-2 infectivity to these pets in this way. These pets may then become a source of virus for their owners. The likelihood and impact of this pathway is unknown due to lacking data on SARS-CoV-2 occurrence in UK deer species as well as the subsequent steps in this pathway, but is likely to be lower in comparison to the ongoing major person-to-person pathway of human infection.

Indirect exposure through contact with contaminated environments

Potential pathways of exposure to humans are via contaminated soil, surface water, ground water and run off, plant surfaces and other surfaces (for example mineral licks, deer rubs and scrapes). Accidental contact with these materials and surfaces is theoretical, but unlikely, routes of exposure.

Appendix 1. Non-food pathways for human exposure to SARS-CoV-2 from deer in the UK

References

1. United States Department of Agriculture Animal and Plant Health Inspection Service. Confirmation of COVID-19 in Deer in Ohio 2021

2. Chandler JC and others. SARS-CoV-2 exposure in wild white-tailed deer (Odocoileus virginianus). Proceedings of the National Academy of Sciences of the United States of America 2021: volume 118, e2114828118

3. Cool K and others. Infection and transmission of ancestral SARS-CoV-2 and its alpha variant in pregnant white-tailed deer bioRxiv 2021.2008.2015.456341

4. Palmer MV and others. Susceptibility of White-Tailed Deer (Odocoileus virginianus) to SARS-CoV-2. Journal of Virology 2021: volume 95, e00083-00021

5. Pickering B and others. Divergent SARS-CoV-2 variant emerges in white-tailed deer with deer-to-human transmission. Nature Microbiology 2022: volume 7

6. Hale VL and others. SARS-CoV-2 infection in free-ranging white-tailed deer. Nature 2021: volume 602

7. Keri VC and others. Needle Stick Injury From a COVID‑19 Patient—Fear It or Forget It? Bioethical Inquiry 2021: volume 18:377–378

8. Langbein J. Monitoring deer vehicle collisions in England to end 2010. The Deer initiative 2011