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Evidence collection21 October 2020

COVID-19 and animals

Evidence-based veterinary medicineEquineExoticsSmall animalsFarm animalsMedicine

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Published 20 April 2020 | Updated 31 October 2025

Introduction

COVID-19 is the official designation of the human disease caused by the novel Coronavirus (SARS-CoV-2, Severe Acute Respiratory Syndrome Corona Virus2) first identified in Wuhan China in December 2019.

Coronaviruses are a large family of RNA viruses that are commonly found in humans as well as other mammals, birds, and reptiles. They all have a characteristic crown (‘corona’) of protein spikes around their lipid envelope. However, the common coronaviruses causing respiratory or gastrointestinal disease in our veterinary patients are alpha coronaviruses, whereas the SARS-CoV-2, is a beta coronavirus, closely related to the viruses that cause SARS and MERS.

Genomic analyses of SARS-CoV-2 indicated that mutations of the receptor binding domain (RBD) of the spike protein present on the surface of the virus optimised the ability to bind to angiotensin-converting enzyme 2 (ACE2) receptors present on the surface of human cells. It has been suggested that SARS-CoV-2 originated either through natural selection in an animal host before zoonotic transfer or as a result of natural selection in humans following zoonotic transfer1.

A recently published paper identified key interactions between spike protein and host receptor ACE2, as the means of both the cross-species and human-to-human transmissions of SARS-CoV (the virus that causes SARS). The authors predict that SARS-CoV-2 also uses ACE2 as its receptor and that the virus could also bind to ACE2 in pigs, ferret, cats and some non-human primates with similar efficiency as it does in people2.

There are three ways that animals could be involved in COVID-19:

  1.  They could be contaminated with live virus and act as fomites
  2. They could become infected with SARS-CoV-2 and develop signs of infection
  3. They could become infected and pass on the virus to other animals or humans.

Current evidence indicates that the predominant route of transmission of COVID-19 is from human to human. However, there are now reports of a small number of companion animals becoming contaminated or infected after close contact with infected people. The World Organisation for Animal Health (OIE) reports that studies are underway to better understand the susceptibility of different animal species to the COVID-19 virus and to assess infection dynamics in susceptible animal species, but that there is no evidence to suggest that animals infected by humans are playing a role in the spread of COVID-19. Human outbreaks are driven by person to person contact3.

It should be noted that when reviewing case reports and published papers three different types of tests are referred to:

PCR (Polymerase Chain Reaction): this test detects the presence of viral genetic material (in this case RNA) but cannot distinguish between infection and contamination.

Antibody tests, which can include Enzyme-Linked Immunosorbent Assays (ELISAs) and Virus Neutralization Tests: detect the presence of antibody to the virus. A positive antibody test indicates that the animal has mounted an immune response to the virus, but does not give any information on whether the animal was clinically ill or has shed the virus at any time.

Virus isolation: used to test for the presence of live virus, and a positive test means that an animal has the potential to shed live virus.

References

  1. Anderson, Kristian G et al (2020) The proximal origin of SARS-CoV-2 Nature Medicine 26 pp 450-452 https://doi.org/10.1038/s41591-020-0820-9
  2. Wan, Yushan et al. (2020) Receptor recognition by novel coronavirus from Wuhan: an analysis based on decade-long structural studies of SARS. Journal of Virology 2020 94 (7) e00127-20  https://doi.org/10.1128/JVI.00127-20
  3. OIE (2020) Questions and Answers on the 2019 Coronavirus Disease (COVID-19) [online] Available at https://www.woah.org/fileadmin/Home/MM/A_COVID-27.11.2020.pdf. [Accessed 23 September 2025]

Case reports

There have been a small number of reports of animals being infected with SARS-CoV-2. To date, all these animals appear to have been infected through contact with infected people. There is no evidence of humans being infected through contact with domestic animals.

There continue to be further case reports of pet animals infected with SARS-CoV-2, in all cases these appear to come from households in which at least one person is infected with COVID-19.

A full list of case reports of confirmed infection of SARS-CoV-2 in animals (Events in animals tab) can be found on the OIE website.

SARS-ANI VIS: a global open access dataset of reported SARS-CoV-2 events in animals.  [Complexity Science Hub, Vienna] [online]. Available from: https://vis.csh.ac.at/sars-ani/#infections [Accessed 10 August 2022].

Variants (Delta and Alpha)

Variant (Omicron)


Variant B.1.1.529 (Omicron)

Variant B.1.617.2 (Delta)

Variant B.1.1.7 (Alpha)

Case reports reporting infection of cats and dogs with alpha variant (B.1.1.7.)

Hamsters Hong Kong

There have been multiple reports in the news of hamsters from a pet shop in Hong Kong being culled, and that other pet shops selling hamsters must suspend business, over fears of the spread of COVID.

While it has been known for some time that hamsters can be experimentally infected with SARS-CoV-2 and spread the virus to other hamsters, to date there have not been any reports of natural infection or any evidence that they can transmit the virus to other species.

The Agriculture, Fisheries and Conservation Department (AFCD) in Hong Kong have released the following statement, which reports that 11 hamsters have so far given preliminary positive tests for SARS-CoV-2, while all other animals tested have tested negative.

From pet hamsters to humans

This paper, currently in preprint, reports on the investigation of SARS-CoV-2 infection in hamsters at a pet shop in Hong Kong and provides some preliminary evidence of transmission of infection from hamsters to humans.

The first human case was a 23-year-old female vaccinated pet shop worker (Patient 1), presented with sore throat and cough, confirmed to be infection with COVID (VOC Delta -AY127 virus lineage). She has no known contact with infected humans.

A mother (patient 2) and her daughter who visited the pet shop and purchased a hamster, also tested positive for SARS-CoV-2 on PCR tests. Subsequently two other members of the household were also confirmed to be infected.

Initial screening of the animals in the pet shop, hamsters (n=69), rabbits (n=42) and Guinea pigs (n=14) returned seven (10.2%) positive swabs from hamsters while none of those from other animals tested positive by RT-PCR. The wholesale warehouse supplying this pet-shop chain was then investigated, with 511 swabs collected from hamsters (n=137), rabbits (n=204), Guinea pigs (n=52), chinchilla (n=116) and mice (n=2) housed there. Here one Syrian hamster swab was RT-PCR positive for SARS-CoV-2.

Since the initial screening suggested that hamsters were infected at both the warehouse and the pet shop, a more detailed sampling was carried out at both sites with swabs and serum being collected from the Syrian and dwarf hamsters.

At the pet shop 8 (50%) of 16 Syrian hamsters had evidence of infection, either by serology or confirmed RT-PCR, with 4 animals testing positive by both serology and RT-PCR, 3 animals tested positive by RT-PCR alone and 1 animal tested positive by serology alone. A total of 3 cages housing Syrian hamsters were sampled and two (66.7%) had animals with confirmed RT-PCR or serology results. In contrast, none of 20 cages housing dwarf hamsters were positive in either RT-PCR or antibody assays.

At the warehouse twelve Syrian hamsters and 55 dwarf hamsters were sampled. Two (16.7%) of the swabs were RT-PCR positive and seven (58.3%) of the sera from Syrian hamsters, had evidence of antibody. The authors interpreted the detection of 5 animals with antibodies but without viral RNA to suggest that infection may have occurred at an earlier date.

Investigation into the source of the infected hamsters suggested that they were imported from Netherlands to Hong Kong in two different batches (arrival dates: 22-December-2021 and 7-January-2022) and that some hamsters arriving on the 7-January-2022 were transferred to pet shop A on the day of arrival.

The virus sequenced from the hamsters were genetically closely related to recent AY.127 viruses detected in multiple European countries. By contrast, none of the AY.127 sequences previously detected from returning travellers in Hong Kong is genetically similar to the sequences detected in this outbreak. This further supports the hypothesis that this outbreak was caused by a recent introduction of AY.127 virus from Europe.

Specimens from the first 3 human cases (Patients 1-3) and positive hamster samples collected in pet shop A (n=11) and the warehouse (n=1) were subjected to full viral genome sequence analysis. The viral genomes all belong to the Delta AY.127 viral lineage.

While the sequences from these human and hamster cases were highly similar, they were not identical. The divergent date of this cluster of human and hamster viruses is estimated to be on 21-November-2021 (; 95% CI range: 18-October-2021 to 16- December-2021). Interestingly, the viral genome of the pet shop worker (patient 1) was phylogenetically distinct (5 nucleotides different) from those of the mother (patient 2) and her husband (patient 3), which were identical.

The authors considered that these results suggest that Patient 1 and Patient 2 acquired the infection independently from hamsters at the pet shop rather than from each other. As Patient 3 did not visit the pet shop, these findings further suggest that the SARS-CoV-2 virus circulating in hamsters allowed at least 1 human-to-human transmission.

The authors conclude that pet hamsters can acquire SARS-CoV-2 infection in real-life settings and can transmit the virus back to humans.

Please note this paper has been published as a preprint and has not been subject to peer review.

Further information

For anyone looking for further details of the pathogenesis and signs of SARS-CoV-2 in hamsters, the following two papers may be of interest.

This paper reports on the presence of viral antigens in nasal mucosa, bronchial epithelial cells and areas of lung consolidation on days 2 and 5 after inoculation with SARS-CoV-2, followed by rapid viral clearance at 7 days after inoculation. They also detected viral antigens in epithelial cells of the duodenum and detected viral RNA in faeces.

It was found that SARS-CoV-2 was transmitted efficiently from inoculated hamsters to naive hamsters by direct contact and via aerosols. However, transmission via fomites in soiled cages was not as efficient.

Although viral RNA was continuously detected in the nasal washes of inoculated hamsters for 14 days, the communicable period was short and correlated with the detection of infectious virus but not viral RNA.

This paper shows that, as in humans, hamsters appear to show an age dependent response to infection with SARS-CoV-2, with young hamsters launching earlier and stronger immune response and older hamsters showing a more pronounced and consistent weight loss.

In providing advice for those who own or handle hamsters the following resources may be helpful

Experimental studies

Experimental studies into the infection and transmission of SARS-CoV-2 by animals are at a very early stage, with information being released rapidly and, in some cases, before peer review has been completed.

The preliminary results of these studies appear to indicate that some domestic animals can be experimentally infected with SARS-CoV-2 and may transmit the virus to other animals, of the same species, under experimental conditions. However, it is important to remember that these are small scale preliminary studies and not to over-interpret the results or extrapolate from the experimental situation to companion animals kept as pets. It is therefore important to interpret the findings of these experimental studies with caution.

Diagnostic testing

Vaccination

Simulation of COVID-19 in golden Syrian hamster model

Susceptibility of ferrets, cats, dogs, and different domestic animals to SARS-CoV-2

Sub-adult cat (8 months)

Note: not all samples collected as difficult to handle

Kitten (70- 100 days)

Dogs (3-month-old beagles)

Finally, the researchers investigated the susceptibility of pigs, chickens, and ducks to SARS-CoV-2 by using the same strategy; however, viral RNA was not detected in any swabs collected from these virus-inoculated animals or from naïve contact animals.

The authors found that SARS-CoV-2 infects the upper respiratory tracts of ferrets but is poorly transmissible between individuals. In cats, the virus replicated in the nose and throat and caused inflammatory pathology deeper in the respiratory tract, and airborne transmission did occur between pairs of cats. Dogs appeared not to support viral replication well and had low susceptibility to the virus, and pigs, chickens, and ducks were not susceptible to SARS-CoV-2.

While this study does show that cats and ferrets can become infected with the SARS-Cov-2 virus, it is important to remember that this is a very small study and that the direct inoculation of virus intranasally may overestimate the risk of infection under normal conditions. It is also important to be aware that this study does not provide any evidence in regards to the ability of cats and ferrets to pass on the infection to humans or other species.

Experimental infection of fruit bats, ferrets, pigs and chicken with SARS-CoV-2

Experimental studies in dogs

Experimental studies in cats

This paper reports on another small experimental study looking at susceptibility to infection with SARS-CoV-2 in dogs and cats. The study includes 3 small groups of animals.

In group 1, three cats were inoculated with virus and oro-pharyngeal swabs were collected on days 1–5, 7, 10, and 14 post infection (DPI), nasal flushes were performed on 1, 3, 5, 7, 10, and 14 DPI and blood was collected prior to inoculation and on 7, 14, 21, 28, 35, and 42 DPI.  These cats were also reinoculated on day 42 from the initial infection. Oronasal sample collection was performed 1, 3, 5, 7, 10, and 14 days after reinoculation (days 29, 31, 33, 35, 38, and 42 post initial inoculation), at which time cats were euthanized and tissues collected for histopathology.

In group 2, two out of four cats were inoculated with SARS-CoV-2 and forty-eight hours post infection, two naive cats were introduced into the room with the infected cats and sampled on the same schedule as for group 1. The two directly challenged cats were euthanized on 5 DPI and tissues were collected for virus isolation and histopathology. The remaining two cats were euthanized at 30 DPI and necropsied.

Group 3 consisted of three dogs. Dogs were sampled at the same frequency and using the same methods as cats in Group 1 for 42 DPI. Dogs were not rechallenged.

The authors report that neither species developed clinical disease during this study. All directly inoculated cats shed virus for up to 5 days, the in-contact cats shed infectious virus orally by 24 hour post exposure, and shedding was prolonged with a peak occurring at 7 days. Viral shedding was not detected from any of the dogs at any point post infection or in cats following rechallenge.

All cats developed neutralizing antibodies as early as 7 DPI with titres of at least 1:2,560 by 14 DPI and either maintained or increased in titre between 28 and 42 DPI. Dogs developed neutralizing antibodies by 14 DPI and peaked at 21 DPI with titres between 1:40 and 1:80.

The authors conclude that cats are highly susceptible to infection, with a prolonged period of oral and nasal viral shedding that is not accompanied by clinical signs and are capable of direct contact transmission to other cats. Conversely, they found that dogs do not shed virus following infection but do seroconvert and mount an antiviral neutralizing antibody response.

This paper confirms the finding of other studies showing that both dogs and cats can be infected with SARS-CoV-2 under experimental conditions, that infected cats are able to pass on the infection and that both species seroconvert. However, these studies do not give any information about the likelihood of animals becoming infected or transmitting infection under non-experimental conditions, where the viral load is likely to be less.

This is another small experimental study looking at response to exposure and transmission to SARS-CoV-2 in both cats and dogs. There were three parts to this study.

ANIMALSInterventionResults
Cats – Group 1 (3 cats)Inoculated intranasally with SARS-CoV-2None of the cats became clinically ill
Nasal and oral swabs taken on days 1,3, 5, 7, 10 and 14 for virus isolation and qPCRCats shed virus for up to 5 days with peak shedding at day 3
Viral levels from nasal swabs were higher than from oral swabs
Blood collected weekly for 6 weeks for ELISA antibody measurementInfected cats all developed detectable antibody by day 7, reaching or exceeding 1:2560 by day 14. Antibody titres stayed stable or increased between days 28-42
Re-exposed to virus at day 28Moderate increase in antibody titres noted 14 days after exposure
Further swabs taken 1, 3, 7, 10 14No viral shedding detected after re-exposure
Euthanased at day 42All three cats had mild lung changes, including mild interstitial lymphocytic pneumonia with peribronchiolar and
perivascular lymphocytic cuffing and alveolar histiocytosis.
Cats – Group 2 (4 cats)Two cats inoculated with SARS-CoV-2 intranasally then co-housed with two other cats 48 hrs later.
Nasal and oral swabs taken on days 1, 3, 5, 7, 10 and 14Inoculated cats shed virus as group 1. Contact cats started shedding within 24 hours of being housed with infected cats but had more prolonged shedding with peak at 7 days post exposure
Blood collected weekly for 6 weeksAll cats developed an antibody response
2 Inoculated cats euthanased on day 5Virus was isolated from trachea, nasal turbinates and oesophagus but was not found in the lung or other organs of
either cat.
Dogs (3 dogs)Inoculated intranasally with SARS-CoV-2None of the dogs developed signs of disease
Nasal and oral swabs taken on days 1-5, 7, 10 and 14Viral shedding not detected
Blood collected weekly for 6 weeksDogs developed neutralizing antibodies by 14 DPI and peaked at 21 DPI with titres between 1:40-1:80

The authors conclude that cats are highly susceptible to subclinical infection, with a prolonged period of oral and nasal viral shedding, that is not accompanied by clinical signs. The study again shows that cats can become infected through direct contact with other infected cats. The authors also state that cats develop a robust neutralizing antibody response that prevented re-infection to a second viral challenge.

The dogs in this study did not appear to shed virus but did mount a low-level antibody response.

A letter published in the New England Journal of Medicine reports on a small experimental study looking at the nasal shedding of SARS-CoV-2 from inoculated cats and the subsequent transmission of the virus by direct contact (co-housing in close contact) in three pairs of cats.

The cats were all between 15 and 18 weeks of age and from a specific pathogen free colony. Nasal and rectal swabs were obtained daily and immediately assessed for infectious virus. None of the cats in the study showed any symptoms, including abnormal body temperature, substantial weight loss or conjunctivitis. All the animals had IgG antibody titres between 1:5120 and 1:20,480 on day 24 after the initial inoculation.

This study supports other evidence that cats can be infected with and transmit SARS-CoV-2 to other cats when in close confinement but gives no information on what may happen under more normal conditions.

Experimental studies in exotics

Experimental studies in ferrets/minks

Experimental studies in farm animals

Experimental studies in horses

Experimental studies in wildlife and zoo animals

Epidemiological studies

There have now been a number of prevalence studies published, and reported in the news, providing details of levels of infection with SARS-CoV-2 in companion animals. In interpreting and comparing the results of these studies is important to be clear about what population of animals is being sampled, general population or those owned by people with confirmed COVID-19 infection and which tests are being carried out (antigen or antibody).

On 20th March, IDEXX Laboratories reported1 that they had tested thousands of canine and feline specimens during validation of a new veterinary test system for the COVID-19. The samples originated from the United States and South Korea, and IDEXX has now expanded monitoring to Canada and European countries and has seen no positive results in pets to date.

Although they state that sampling included areas with high rates of COVID-19 in the human population, details of the sampling strategy and timing were not given.

Reference

1. IDEXX (2020) IDEXX SARS-CoV-2 (COVID-19) RealPCR Test [online] Available at: https://www.idexx.com/en/about-idexx/covid-19-resources/#results [Accessed 20 April 2020]

Cats and dogs

Epidemiological study from Poland which detected a seroprevalence of 1.79% (95% CI: 0.77 – 4.13) of 279 cats and 1.17% (95% CI 0.45 – 2.96) of 343 dogs. This study also included 29 rabbits, none of which tested positive for SARS-Co-V-2 antibodies.

This paper reports on the presence of SARS-CoV-2 viral antigen and antibodies in 1,516 animals, 492 of which had known contact with people who had tested positive for COVID and 1,024 others. Only 12 animals (eight dogs and four cats) 0.79% of the total (n = 1516), were positive for viral SARS-CoV-2 RNA detected by reverse transcription quantitative PCR (RT-qPCR) and viral isolation was possible in four animals.  Neutralizing antibodies were detected in 34 animals (20 dogs and 14 cats), four of which were also positive for PCR.

This paper reports on the seroprevalence of SARS-CoV-2 antibodies in blood samples from 2,160 cats from UK, Germany, Italy and Spain submitted to a diagnostic laboratory, between April and June 2020. The study found overall SARS-CoV-2 seroprevalence among cats was 4.2% in Germany, 3.3% in the United Kingdom, 4.2% in Italy, and 6.4% in Spain.

This short communication reports on the prevalence of SARS-CoV-2-positive cats and dogs from ten infected mink farms in the Netherlands, and their possible role in transmission of the virus.

Throat and rectal swabs of 101 cats (12 domestic and 89 feral cats) and 13 dogs were tested for SARS-CoV-2 using PCR. Eleven cats (18%) and two dogs (15%) tested serologically positive. Three feral cats (3%) and one dog (8%) tested PCR-positive.

The authors conclude that as only feral cats were infected it is most likely that infections in cats were initiated by mink, not by humans. Whether both dogs were infected by mink or humans remains inconclusive.

This paper reports on the prevalence of SARS-CoV-2 neutralising antibodies in residual sera from dogs and cats whose blood was submitted to diagnostic laboratories for routine diagnostic testing. Sera collected pre Covid and during the “first wave” (March and April 2020) all tested negative for SARS-CoV-2 neutralising antibodies.

Sera from 4/287 (1.4%) dogs and 2/90 (2.2%) cats collected during the “second wave” (Sept 2020-Feb 2021 for dogs and Jan2021 for cats) tested positive for SARS-CoV-2 neutralising antibodies.

The authors concluded that based on the low numbers of animals testing positive pet animals are unlikely to be a major reservoir for human infection in the UK. However, continued surveillance of in-contact susceptible animals should be performed as part of ongoing population health surveillance initiatives.

This paper reports on the seroprevalence of SARS-CoV-2 in 656 dogs and 131 cats admitted to three veterinary facilities in Croatia between 26 February 2020 and 15 June 2020. Additionally, on 25 May 2020, a total of 122 serum samples from employees of the Faculty of Veterinary Medicine University of Zagreb were collected.

Neutralising antibodies were confirmed in 0.76% cats and 0.31% dogs using the microneutralisation test (MNT). ELISA reactivity was recorded in 7.56% tested dog sera. While 5.19% of administrative, basic and pre-clinical sciences department personnel and 5.13% of animal health service providers and laboratory personnel tested ELISA positive.

The authors note that it is possible that a portion of dogs which tested ELISA positive were sampled early or late in the course of the infection when antibody titre is low. However, it is also possible that the number of dogs in field conditions develops only mild infections resulting only in ELISA reactivity of their serum samples with no measurable neutralising antibodies.

The authors conclude that infections in dogs and cats are rare and are following infections in the human population and that contact with animals does not seem to be an occupational risk for veterinary practitioners.

This paper reports on evidence of infection with SARS-CoV-2 in 39 pets (29 dogs and 10 cats) living with COVID-19 patients in Rio de Janeiro, during the period May-October 2020. Animals were tested for SARS-CoV-2 antigen (nasopharyngeal/oropharyngeal and rectal swabs) and for SARS-CoV-2 antibodies (blood sample) on 3 separate occasions approximately 15 days apart.

Nine dogs (31%) and four cats (40%) from 10 (47.6%) households showed evidence of infection with SARS-CoV-2. Six of these 13 animals developed mild but reversible signs of the disease.

Animals tested positive from 11 to 51 days after the human index COVID-19 case onset of symptoms. Three dogs tested positive twice within 14, 30, and 31 days apart. SARS-CoV-2 neutralizing antibodies were detected in one dog (3.4%) and two cats (20%).

The authors conclude that people diagnosed with COVID-19 should avoid direct contact with their pets for as long as they remain ill.

This paper reports on the levels of infection with SARS-CoV-2 of cats in animal shelters during the “second wave” of human COVID-19 infections in The Netherlands (August 2020 to February 2021).

Seroprevalence was determined by using an indirect protein-based ELISA validated for cats, and a Virus Neutralization Test (VNT) as confirmation. Two of these cats (0.8%; CI 95%: 0.1–3.0%) were seropositive, as evidenced by the presence of SARS-CoV-2 neutralizing antibodies. The seropositive animals tested PCR negative for SARS-CoV-2. Based on the results of this study, it is unlikely that shelter cats act as a reservoir of SARS-CoV-2 or pose a (significant) risk to public health.

This research letter reports on prolonged SARS-CoV-2 infection in a therapy cat from a nursing home in Germany which had 21 confirmed human infections (15 residents and 6 staff), including three deaths during a cluster outbreak starting in April 2020.

As part of the epidemiologic investigation of this outbreak the three therapy cats were also tested for SARS-CoV-2 by using conjunctival, faecal and oropharyngeal swabs. The cats were transferred to the BSL-3 animal facility at the University of Veterinary Medicine Hannover, for detailed follow-up. Cat K8, the close companion of one of the patients who died, was confirmed to be SARS-CoV-2 positive by quantitative real-time quantitative reverse transcription PCR.

The cats were housed together after the first four days and repeat testing at regular intervals showed that cats K4 and K9 remained negative, whereas K8 was positive for SARS-CoV-2 RNA until day 21 of surveillance.

The authors report that genomic sequencing supports direct human-to-cat-transmission during the first outbreak but not zoonotic SARS-CoV-2 transmission from K8.

It should be noted that more detail of epidemiological investigation and genomic sequencing is provided in the Appendix.

This paper reports on a serological study of 114 stray cats sampled as part of a trap neuter release sterilisation program carried out in Zaragoza (Spain) from January to October 2020. The cats were tested for SARS-CoV-2, Toxoplasma gondii, Leishmania infantum, feline leukaemia virus (FeLV), feline immunodeficiency virus (FIV) and feline coronavirus (FCoV).

The seroprevalence of SARS-CoV-2 infection was 3.51%. with 4 out of 114 cats testing seropositive by ELISA. Of these three cats were found to have co-infection: one male co-infected with T. gondii and FIV, one male co-infected only with FIV and L. infantum, and a female co-infected only with T. gondii.

The presence of other co-infections was also detected including T. gondii and FIV (n = 3), T. gondii and L. infantum (n = 3), FeLV and FIV and L. infantum (n = 1), FeLV and FIV (n = 1), FeLV and L. infantum (n = 1), and FIV and L. infantum (n = 5).

The authors noted that while the seroprevalence of SARS-CoV-2 in stray cats in this sample was low the existence of concomitant infections with other pathogens including T. gondii, L. infantum and FIV, may suggest that immunosuppressed animals might be especially susceptible to SARS-CoV-2 infection.

This paper reports on the development and validation of SARS-CoV-2 PCR test for use in animals. The test was then used to establish the frequency of SARS-CoV-2 in samples from 4616 dogs and cats submitted for testing for respiratory pathogens to IDEXX laboratories in Asia, Europe and North America between mid-February and mid-April 2020.  The frequency of respiratory pathogens detected was then compared for the periods February–April 2019 and 2020.

Conjunctival and deep pharyngeal swabs were submitted for each patient. If multiple samples were submitted for an individual patient during the study window, only the first sample was included in the analysis.

Samples from 2150 dogs and 2466 cats were tested and 44% of canine and 69% of feline samples were PCR positive for at least one respiratory pathogen with Mycoplasma cynos and Bordetella bronchiseptica the most commonly detected pathogens in dogs,  and Mycoplasma felis and feline calicivirus, the most commonly detected pathogens in cats. No SARS‐CoV‐2 infections were identified. Positive results for respiratory samples were similar between years.

As part of the development, cross‐specificity testing to rule out false positives caused by other veterinary coronaviruses was performed using veterinary patient samples that had tested positive at IDEXX Reference Laboratories.  Commercially available PCR tests were used for the  canine respiratory coronavirus (CrCoV -30 samples),  canine enteric coronavirus (CeCoV -30 samples),  feline enteric coronavirus (FeCoV -30 samples) and equine coronavirus( ECoV -two samples). None of these samples had a positive result with the SARS‐CoV‐2 real‐time PCR. None of the 55 human patient isolates (36 SARS‐CoV‐2 positive and 19 SARS‐CoV‐2 negative) tested were positive for the CrCoV, CeCoV, FeCoV or ECoV.

The authors conclude that these data suggest there is currently no need for widespread SARS‐CoV‐2 testing in the dog and cat population since naturally occurring clinical infections are rare in dogs and cats. Practitioners should continue to consider and test for common respiratory pathogens before SARS‐CoV‐2 infection is considered in pet dogs and cats with respiratory signs.

It should be noted that this study was carried out early in the COVID pandemic which may have affected both the number samples submitted and the respiratory pathogens.

This paper reports on a series of dogs and cats presenting with myocarditis at a single referral centre, on the outskirts of London, between December 2020 and February 2021. The authors reported the incidence of myocarditis at their practice of 12.8% (8.5% in cats and 4.3% in dogs) compared with an expected incidence of 1.4%.

The animals presented with acute onset of lethargy, inappetence, tachypnoea /dyspnoea (secondary to congestive heart failure) and in some cases syncope. None of these patients had a previous history of heart disease and none developed symptoms of respiratory tract infection.

Diagnostic investigations revealed the presence of elevated cardiac troponin-I (median 6.8; range 0.68 to 61.1 ng/mL [normal reference range 0.0-0.2 ng/mL]) accompanied by echocardiographic evidence of myocardial remodeling and/or signs of pleural effusion and/or pulmonary edema, often confirmed on thoracic radiographs and/or severe ventricular arrhythmias on electrocardiography.

All affected animals were reported to have made a remarkable improvement with cage rest, oxygen therapy, acute diuresis and, in some cases, anti-arrhythmic therapy with sotalol and fish oil supplementation before being discharged on oral medications after a few days of intensive care. However, one cat represented one week after discharge with a relapse of her clinical signs, characterised by profound lethargy and uncontrolled ventricular tachycardia, prompting her owners to elect for euthanasia.

As these cases coincided with an outbreak of the B1.1.17 variant of SARS-CoV-2 in the UK, and many of the owners had tested PCR positive for SARS-CoV-2 infection in the 3-6 weeks before their animals became ill, the authors decided to investigate SARS-CoV-2 infection in these animals.

Serum samples as well as oro/nasopharyngeal and rectal swabs were collected from seven animals (six cats and one dog) at initial presentation and blood samples from four other pets (two cats and two dogs) during their recovery, 2-6 weeks after they developed signs of myocarditis.

Samples were frozen and sent to France for serological and virological investigation. All oro/nasopharyngeal swabs were negative for SARS-CoV-2 on PCR. However, the authors report low viral loads were detected from the rectal swabs from three of seven animals (two cats and one dog), and analysis of regions of the spike protein gene indicated the B.1.1.7 variant. One animal sampled during the acute phase of the disease (which tested PCR negative) and two of four animals sampled during the recovery period, were found to have SARS-CoV-2 antibodies.

While these results indicate that 6 of the 11 animals tested had some evidence of exposure to SARS-CoV-2 further research will be needed to investigate whether there is a causal link to myocarditis in pets and whether new variants of SARS-CoV-2 have a higher transmissibility or pathogenicity in animals.

This study is a pre-print, made available by bioRxiv, as such it is only a preliminary report and has not yet been peer-reviewed.

This letter reports on the results of samples taken from 50 cats during 11 February – 11 August, 2020.  At this time, as a precautionary measure mammalian pets from households with confirmed human coronavirus disease (COVID-19) or their close contacts (defined as a person who had face-to-face contact for >15 minutes with a person who had confirmed SARS-CoV-2 infection were quarantined by the Agriculture, Fisheries and Conservation Department of Hong Kong.

The cats were swabbed (nasal, oral, rectal) for SARS-CoV-2 and confined until reverse transcription PCR (RT-PCR) results are negative on two consecutive occasions. SARS-CoV-2 RNA persisted longest in nasal secretions, in one case for 11 days at low levels.

Time from onset of COVID-19 symptoms in owners to first sampling of their cats was available for 21 owners of 35 cats and ranged from 3 to 15 (median 8, interquartile range 4) days. SARS-CoV-2 RNA was detected in samples from 6 (12%) of 50 cats. Signs of disease did not develop in any cats.

The timeline of infection in cat 1 (which had no outdoor access) and the finding of an identical SARS-CoV-2 genome sequence in a human from the same household is consistent with human-to-animal transmission. Although feline-to-human transmission is theoretically possible, the authors did not find any evidence of this transmission

This paper present results from a serological survey of pets conducted between May and June 2020 in two neighbouring regions of eastern France (Franche-Comté and Rhone-Alpes). Both regions were reported to have similar epidemiological characteristics and health management policies, with the first hospitalised deaths registered in March 2020.

The first group of pets, from the Franche-Comté region, were living in homes where at least one person tested positive for SARS-CoV-2 (COVID-19+ household group). The second group, from the Rhone-Alpes, were pets from households where exposure was unknown (unknown status household group). Lastly, they included a control group of animals sampled in 2018 and early 2019 before the outbreak, including hyperimmune sera from ten cats with feline infectious peritonitis virus (FIPV), (Control group). FIPV-infected cat sera were included in the control group to exclude possible cross-reactivity of antibodies generated in response to non-SARS-CoV-2 coronaviruses.

The researchers combined four different tests based on two different techniques to ensure the greatest degree of specific-antibody detection. Three microsphere immunoassays (MIA) detected anti-SARS-CoV-2 IgGs produced in response to viral N, S1, or S2 proteins, and a retrovirus-based pseudo-particle assay detected SARS-CoV-2 neutralizing antibodies.  Animals were declared COVID-19 positive following a positive sero-neutralization assay or if they were positive for all three MIA tests.

21.3% (10 of 47 animals tested) of pets in COVID-19+ households tested positive, including 23.5% of cats (8/34) and 15.4% of dogs (2/13). Out of the 16 cats and 22 dogs tested from households of unknown status, only one animal (a cat) tested positive and none of the animals in the control group tested positive.

However, if only one test was required to be positive 53.2% in pets from COVID-19+ households showed signs of having been infected (58.8% of cats (20/34) and 38.5% of dogs (5/13)) compared to 15.8% (6/38) of pets in homes of unknown status.

The authors conclude that, based on the highly variable antibody responses to SARS-CoV-2 reported in human infections, and a recent Swiss study that found that anti-N antibody assays substantially underestimate the proportion of SARS-CoV-2 exposed individuals compared to anti-S antibody assays in population-based seroprevalence studies, the actual seropositivity in COVID-19+ households is likely closer to 53% than 21%, indicating that infection risk in the pets of COVID-19 positive owners is much higher than previously described.

This study shows that it is important to be aware of exactly what testing criteria have been used when interpreting results and comparing results from different studies.

This paper reports on an epidemiological survey to assess SARS-CoV-2 infection in 817 dogs and cats, living in northern Italy and sampled between March and May 2020, at a time of frequent human infection.

A total of 540 dogs and 277 cats were sampled from different Italian regions, mostly Lombardy (476 dogs, 187 cats). All animals were sampled by their private veterinary surgeon during routine healthcare visits and a range of samples were taken:

For 340 dogs and 188 cats, full signalment and clinical history were available, including breed, sex, age, exposure to COVID-19 infected humans, and presence of respiratory signs.

Sera were available for 188 dogs and 63 cats for which complete signalment, history and location were available. Additional sera were collected from diagnostic laboratories for 200 dogs and 89 cats from the affected areas, but which lacked further historical information.

No animals tested PCR positive. However, 3.4% of dogs and 3.9% of cats had measurable SARS-CoV-2 neutralizing antibody titres, ranging from 1:20 to 1:160 in dogs and from 1:40 to 1:1280 in cat.

Dogs from COVID-19 positive households being significantly more likely to test positive than those from COVID-19 negative households.

Although this is a large survey it should be noted that not all information was available for all animals, and that lack of confirmed COVID infection in the household does not mean that no-one was infected. However, it does appear to demonstrate that both cats and dogs can seroconvert under the normal conditions of pet ownership, at least where the burden of disease is high in humans.

This paper reports on the serological prevalence of SARS-CoV-2 in a sample of cats in Wuhan, China.
Graphic from abstract of A serological survey of SARS-CoV-2 in cat in Wuhan
In this study, 39 banked sera collected from cats before the outbreak (March to May 2019) and 102 samples collected from cats in animal shelters and veterinary clinics in Wuhan from January to March 2020 (i.e. during the COVID-19 outbreak) were screened by indirect enzyme linked immunosorbent assay (ELISA) for antibody reactivity against recombinant RBD of SARS-CoV-2 spike protein.

15 (14.7%) of the samples collected from January to March 2020 were positive for RBD-based ELISA and 11 of these then showed neutralizing antibodies against SARS-CoV-2 when tested by virus neutralization tests.

The cats with the highest titres belonged to people with confirmed COVID-19. While it may not be surprising that cats in contact with owners infected with COVID-19 can become infected, it is interesting that a number of other cats also mounted some degree of immune response.
It was also noted that both type I and II feline infectious peritonitis virus (FIPV) hyperimmune sera showed no cross-reactivity withSARS-CoV-2 RBD protein.

In addition, the researchers continuously monitored serum antibody dynamics of two positive cats every 10 days over 130 days. The authors reported that serum antibodies reached the peak at 10 days after first sampling and declined to the limit of detection within 110 days.

While this study provides some preliminary evidence that cats can become infected, and mount an immune response raising an antibody response to SARS-CoV-2, it did not give any information on whether the cats are able to pass on the virus.

Image reproduced under Creative Commons CC BY license from A serological survey of SARS-CoV-2 in cat in Wuhan. Emerging Microbes & Infections, 9 (1), p 2013
Reference for pre print:
Zhang, Q. et al. (2020) SARS-CoV-2 neutralizing serum antibodies in cats: a serological investigation bioRxiv https://doi.org/10.1101/2020.04.01.021196

This study, from the Institut Pasteur, reports on the testing of 9 cats and 12 dogs living in close contact with their owners, belonging to a group of 20 veterinary students in which two students tested positive for COVID-19 and several others (n = 11/18) showed clinical signs (fever, cough, anosmia, etc.) consistent with COVID-19 infection, between 25th February and 18th March 2020. Although a few pets were reported to have presented clinical signs indicative of a coronavirus infection; blood samples collected on 25th March and nasal and rectal swabs collected daily for 1 week, starting from the day of blood sampling, all tested negative for virus (PCR) and antibodies (immunoprecipitation).

While this study provides preliminary evidence that animals living with their owners do not become infected, it is important to note that this is a small study and it is possible that the timing of the samples could have missed transient contamination.

Ferrets/minks

Report on genetic characteristics of the U.S. and Canadian mink–derived SARS-CoV2 sequences. The study reports that novel SARS-CoV2 variants are most likely to have evolved during human infection and were then transmitted to mink populations in the United States.

Report of a COVID outbreak in farmed mink in Northern Poland reporting test results and genetic sequencing.

This short communication reports on the prevalence of SARS-CoV-2-positive cats and dogs from ten infected mink farms in the Netherlands, and their possible role in transmission of the virus.

Throat and rectal swabs of 101 cats (12 domestic and 89 feral cats) and 13 dogs were tested for SARS-CoV-2 using PCR. Eleven cats (18%) and two dogs (15%) tested serologically positive. Three feral cats (3%) and one dog (8%) tested PCR-positive.

The authors conclude that as only feral cats were infected it is most likely that infections in cats were initiated by mink, not by humans. Whether both dogs were infected by mink or humans remains inconclusive.

This research letter reports on SARS-CoV-2 infection in 71 ferrets belonging to 7 owners; the ferrets were used as working animals for rabbit hunting in Ciudad Real Province, central Spain. SARS-CoV-2 RNA was found in swab samples (1 rectal and 5 nasal) from 6 (8.4%) of the 71 ferrets from 4 of the 7 groups of ferrets investigated.

The authors conclude that natural SARS-CoV-2 infection in kept ferrets does occur in circumstances of high viral circulation in the human population. However, the high cycle thresholds observed and the lack of virus-positive ferrets at resampling suggest that small ferret populations are less able to maintain prolonged virus circulation than large, farmed mink populations.

This paper reports on a wildlife epidemiologic investigation of mammals captured on or near properties in Utah, USA, where outbreaks of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection occurred in farmed mink.

Free-roaming mammals were captured between August 22–30, 2020, by using Sherman (rodents) and Tomahawk (mesocarnivores) traps placed outside barns and barrier fences on outbreak premises and public lands within a 3.5-km buffer zone. Sample collection included oral, nasal (washes for mice), and rectal swabs as well as tissue and blood samples.

102 mammals were captured (78 rodents and 24 mesocarnivores). Rodents captured consisted of three species of mice and three rock squirrels. Mesocarnivore captures consisted of 11 presumed escaped American mink, two presumed wild American mink, five raccoons and six striped skunks. Presumed escaped mink were closely associated with barns and designated as domestic escapees on the basis of location, behaviour, and appearance.

Wild mink were identified by brown coat colour and smaller size compared with farmed mink.
All escaped mink and rodents, except for four deer mice and one rock squirrel, were caught on farm premises. All raccoons, the two presumed wild mink, and all but one striped skunk were captured off-property but within the buffer zone.

Serum samples from the 11 mink escapees tested positive for SARS-CoV-2 antibodies by virus neutralization, and three also had viral RNA detected by rRT-PCR from nasal swabs and one from lung tissue. A rectal swab specimen from a house mouse had a high Ct detection by rRT-PCR but was negative for SARS-CoV-2 antibodies.

No other animal had a detectable antibody response.

Although the authors did not find evidence for SARS-CoV-2 establishment in wildlife, they note that the discovery of escaped mink with the opportunity to disperse and interact with susceptible wildlife, such as wild mink or deer mice, is concerning and recommend heightened biosecurity to help prevent accidental releases of infected animals or spillover of SARS-CoV-2 from susceptible species to native wildlife.

This paper reports on the epidemiological investigation into SARS-CoV-2 infection at three mink farms in the Northern Jutland region of Denmark, to analyse the transmission of virus in mink and the local human community.

Swab samples (blood and throat, nasal, and faecal swabs) were collected from adult mink and kits from 3 different mink farms. Air and feed samples were also collected. Samples were assessed for viral RNA by quantitative reverse transcription PCR (qRT-PCR) and SARS-CoV-2 Ab ELISA.

At initial sampling, seroprevalence was high on farm 1 (>95%) and farm 3 (66%) but, only 3% on farm 2. However, at follow up sampling seroprevalence on farm 2 had increased to >95%.

The authors note that despite the high level of virus detected in the mink there was little clinical disease or increase in death rate, making it difficult to detect the spread of infection; thus, mink farms could represent a serious, unrecognized animal reservoir for SARS-CoV-2.

Air samples from farm 1 tested negative. However, on farms 2 and 3, multiple samples collected from exhaled air from mink or within 1 m of the cages were positive. None of the air samples collected outside the houses were positive. Feed samples collected at each farm tested negative.

SARS-CoV-2–positive samples were then sequenced. The viruses found on farms 1–3 were very similar and these sequences and those from humans linked to the infected farms grouped within the European 20B clade of the global SARS-CoV-2 tree.

The authors conclude that a likely scenario for the spread of infection in mink in Denmark is that the index human case-patient introduced infection into farm 1, where a mutation occurred that could be linked to subsequent human cases. It seems that the variant viruses on farm 1 spread to >1 human and were then transmitted, presumably by human–human contact, to other people and to farms 2 and 3.

This study reports on the results of a “natural experiment” where 29 ferrets in one home had prolonged, direct contact and constant environmental exposure to two humans with symptomatic COVID-19. The authors observed no evidence of SARS-CoV-2 transmission from humans to ferrets based on RT-PCR and ELISA.

This research was carried out as part of the Coronavirus Epidemiological Response and Surveillance (CoVERS) study, set up at Tufts University to investigate the potential for human-to animal spill over and onward transmission in domestic, farm and wildlife species.

A household with 29 free-roaming ferrets cared for by two adults was enrolled as part of the CoVERS study. Individual 1 experienced fever and fatigue from 25 March-6 April and individual 2 experienced a sore throat, anosmia, migraine and fatigue from 28 March-13 April. Individual 2 tested positive for SARS-CoV-2/COVID-19 infection by nasopharyngeal swab and RT-PCR on 1 April. Individual 1 was a probable positive due to the timing and symptoms but was not tested. Neither person was hospitalised, and both cared for the ferrets during the entirety of their disease courses.

A two-week, in-home sample collection scheme was designed to begin during the household quarantine period, the ferrets were free to move in all spaces of the home during this period and were handled as usual, including regular petting, feeding and grooming.  A home sampling kit sent to the participants including material to safely collect and store ferret oral swabs. One participant had significant animal handling experience and performed all sample collection to standardise sampling procedures. Thirty oral swabs were collected and held in viral transport media in the participants’ freezer until the end of the study period. Frozen samples were directly transferred to a lab member and processed.

Oral swabs were collected from all ferrets in the home over a two-week period, beginning 10 April, concurrent with symptomatic disease in individual 2. One ferret (3) was sampled twice. Two 7-year-old ferrets (12 and 16) died during the study period, one by euthanasia due to chronic disease, the other cause is unknown. Thirty samples from 29 ferret oral swabs were tested by semi-quantitative real time RT-PCR and ELISA.

All samples were confirmed to have viable RNA (by a preliminary screen for constitutively expressed ß-actin) but results of semi-quantitative real time RT-PCR and ELISA were below the limit of detection and determined to be negative for active or recent infection by SARS-CoV-2.

As ferrets have been shown to be susceptible to infection and onward transmission in experimental laboratory infections the researchers undertook further analysis to better understand this discrepancy in experimental and natural infection in ferrets.

They compared SARS-CoV-2 sequences from natural and experimental mustelid infections and identified two surface glycoprotein (Spike) mutations. Evidence found that while ACE2 provides a weak host barrier, one mutation only seen in ferrets is located in the novel S1/S2 cleavage site and is computationally predicted to decrease furin activity. They conclude that the data support that host factors interacting with the  novel S1/S2 cleavage site may be a barrier in ferret SARS-CoV-2 susceptibility and that  domestic ferrets are at low risk of natural infection from currently circulating SARS-CoV-2. This may be overcome in laboratory settings using concentrated viral inoculum, but the effects of ferret host-adaptations require additional investigation.

This paper describes an in-depth investigation of SARS-CoV-2 outbreaks on 16 mink farms, in the Netherlands, and infection in the people living or working on these farms, combining epidemiological information, surveillance data and whole genome sequencing (WGS).

97 individuals were tested by either serological assays and/or RT-PCR. 43 out of 88 (49%) of upper-respiratory tract samples tested positive by RT-PCR while 38 out of 75 (51%) of serum samples tested positive for SARS CoV-2 specific antibodies. In total, 66 of 97 (67%) of the people tested had evidence for SARS CoV-2 infection. To maintain anonymity the farms were grouped into geographic areas for analysis.

The whole genome sequences generated from mink farms and from mink farm employees were compared with the national database consisting of around 1,775 WGS. In addition, to discriminate between locally acquired infections and mink farm related SARS-CoV-2 infection, and to determine the potential risk for people living close to mink farms, WGS was also performed on 34 SARS-CoV-2 positive samples from individuals who live in the same four-digit postal code area as the first four mink farms. These local sequences reflected the general diversity seen in the Netherlands and were not related to the clusters of mink sequences found on the mink farms, giving no indication of spill-over to people living in close proximity to mink farms.

After the detection of SARS-CoV-2 on mink farms, 68% of the tested farm workers and/or relatives or contacts were shown to be infected with SARS CoV-2, indicating that contact with SARS-CoV-2 infected mink is a risk factor for contracting COVID-19.

A high diversity in the sequences from some mink farms was observed which the authors considered was most likely explained by many generations of infected animals before an increase in mortality was observed. They note that mink farms have large populations of animals which could lead to very efficient virus transmission and that the virus might replicate more efficiently in mink or might have acquired mutations which makes the virus more virulent.

A mutation in the spike protein (D614G), that has been shown to result in an increased virulence in vitro, was present in farm clusters A, C and E, but no obvious differences in clinical presentation, disease severity, or rate of transmission to humans was observed.

The authors conclude that the virus was initially introduced from humans and has evolved, most likely reflecting widespread circulation among mink in the beginning of the infection period, several weeks prior to detection.

Please note this paper has been published as a preprint on bioRxiv and has not been subject to peer review.

Bats

This paper reports on a qualitative disease risk analysis (DRA), undertaken to assess the risk of disease from SARS‐CoV‐2 to free‐living bats from fieldworkers carrying out bat conservation interventions and development activities in England. The probability of disease occurring and the magnitude of the possible consequences to bat populations were assessed and mitigation methods proposed.

The disease risk assessment was carried out by staff from The Institute of Zoology and Natural England, according to the method described by the OIE.  Assessment was undertaken of the biological pathways that might permit bats to be exposed and infected with SARS‐CoV‐2, as well as the probability of exposure and infection occurring.

The probability of exposure of bats to SARS‐CoV‐2 through fieldwork activities was estimated to range from negligible to high, depending on the proximity between bats and people during the activity. The likelihood of infection after exposure was estimated to be high and the probability of dissemination of the virus through bat populations medium.

There is uncertainty in the pathogenicity of SARS‐CoV‐2 in bats, with the authors reporting that SARS‐CoV‐2 has been demonstrated experimentally to infect one species of bat, but another has been shown to be experimentally resistant. Therefore, although the likelihood of clinical disease occurring in infected bats was assessed as low there is some uncertainty in this risk estimation. The authors note that the disease risk analysis should be updated as information on the epidemiology of SARS‐CoV‐2 and related viruses in bats improves.

The authors conclude that the probability of infection can be effectively reduced if fieldworkers follow routine government guidance, and minimum precautions have been set out in advice provided by DEFRA to Natural England and in addition follow strict biosecurity measures when contacting bats or possible fomites which may expose bats to the virus, including the use of disposable gloves, cloth face coverings, effective hand cleansing and appropriate disinfecting of equipment.

Guidance

Natural England (2020). COVID‐19 and interacting with wildlife for the purposes surveying and mitigation works [online] Available from: https://www.gov.uk/guidance/coronavirus-covid-19-surveying-and-mitigation-works-affecting-wildlife [Accessed 22 March 2021]

Botto Nunez, G. et al (2020) IUCN SSC Bat Specialist Group (BSG) recommended Strategy for researchers to reduce the risk of transmission of SARS-CoV-2 from humans to bats [online] Available from: https://www.iucnbsg.org/uploads/6/5/0/9/6509077/map_recommendations_for_researchers_v._1.0_final.pdf [Accessed 23 September 2025]

Deer

The U.S. Department of Agriculture has released a report of a surveillance study that analysed serum samples from free ranging white-tailed deer for antibodies to SARS-CoV-2.

Samples were collected in 4 states (Illinois, Michigan, New York, and Pennsylvania) between January 2020 and January 2021. None of the deer populations surveyed showed signs of clinical illness associated with SARS-CoV-2, and evidence of viral shedding was not undertaken. However, antibodies to SARS-CoV-2 were detected in 33% of the 481 samples, indicating exposure. Concerns that the test, which has not yet been validated in deer, may have been cross reacting with anther virus, were addressed by retesting the samples using a test specific to SARS-CoV-2 and testing archived samples from before the pandemic.

The report states that the finding that wild white-tailed deer have been exposed to SARS-CoV-2 is not unexpected given that white-tailed deer are susceptible to the virus, are abundant in the United States, often come into close contact with people, and that, more than 114 million Americans are estimated to have been infected with COVID-19, according to the U.S. Centers for Disease Control and Prevention. However, this level of exposure raises significant questions about this risk of SARS -CoV-2 becoming established in wildlife, and further research is urgently needed.

The U.S. Department of Agriculture has released a report of a surveillance study that analysed serum samples from free ranging white-tailed deer for antibodies to SARS-CoV-2.

Samples were collected in 4 states (Illinois, Michigan, New York, and Pennsylvania) between January 2020 and January 2021. None of the deer populations surveyed showed signs of clinical illness associated with SARS-CoV-2, and evidence of viral shedding was not undertaken. However, antibodies to SARS-CoV-2 were detected in 33% of the 481 samples, indicating exposure. Concerns that the test, which has not yet been validated in deer, may have been cross reacting with anther virus, were addressed by retesting the samples using a test specific to SARS-CoV-2 and testing archived samples from before the pandemic.

The report states that the finding that wild white-tailed deer have been exposed to SARS-CoV-2 is not unexpected given that white-tailed deer are susceptible to the virus, are abundant in the United States, often come into close contact with people, and that, more than 114 million Americans are estimated to have been infected with COVID-19, according to the U.S. Centers for Disease Control and Prevention. However, this level of exposure raises significant questions about this risk of SARS -CoV-2 becoming established in wildlife, and further research is urgently needed.

Equine

Wildlife and zoo

Reviews

This paper, first published on 22 October 2020, presents the findings of a scoping literature review conducted to collect, evaluate and present the available research evidence regarding SARS‐CoV‐2 infections in animals. The authors include both experimental studies and reports of natural infection and conclude that “Most animals are presumed to have been infected by close contact with COVID‐19 patients. In domestic settings, viral transmission is self‐limiting; however, in high‐density animal environments, there can be sustained between‐animal transmission”.

This paper provides a review of reported cases of animals naturally infected with SARS-CoV-2, particularly companion pets, with the aim of shedding light on the role of these animals in the epidemiology of COVID-19. It includes a brief overview of coronaviruses and information on the similarity between the ACE2 protein in various animals and humans, which may have implications for susceptibility to infection with SARS-CoV-2.

This paper reports on an analysis of ACE2 receptors using annotated genomes of marine mammals from the 4 major groups (36 species) in order to generate an index of susceptibility for marine mammals to SARS-CoV-2.

To distinguish between the susceptible and non-susceptible species, the authors used the human ACE2 (high susceptibility), feline ACE2 (medium susceptibility; lower affinity but still susceptible) and dog ACE2 (not susceptible) as reference points. Using this method, they identified that many species of whale, dolphin, and seal, as well as otters, are predicted to be highly susceptible to infection by the SARS-CoV-2 virus.

The authors then looked at wastewater management in certain Alaskan localities and concluded that this may not be sufficient for preventing waterborne exposure of nearby marine mammals to the virus.

They concluded that while the risk to marine mammals is likely very low, especially in terms of creating a sustained problem , since some marine mammal populations are highly threatened, an outbreak localized to an individual pod or population could still have significant consequences.

This paper reports on potential species differences in susceptibility to SARS-CoV-2 using multiple in-depth structural analyses to identify key ACE2 amino acid positions (including 30, 83, 90, 322, and 354) and use these differences to develop a susceptibility score.

The authors conclude that SARS-CoV-2 is nearly optimal for binding ACE2 of humans compared to other animals, which may underlie the highly contagious transmissibility of this virus among humans.

While this study does not give us information about what is happening in terms of infection these species it may provide information to direct future surveillance and research.

The OiE have produced a technical factsheet which provides a brief summary of the current (June 2020) knowledge about SARS-CoV-2 infection in animals. It includes sections on aetiology, epidemiology, diagnosis, and methods of prevention and control. It also includes this table summarising current knowledge about infection in animals.

SPECIESTYPE OF INFECTIONSUSCEPTIBILITYCLINICAL SIGNSTRANSMISSION
PigsExperimentalNoneNoNo
Poultry (chickens, ducks and turkeys)ExperimentalNoneNoNo
DogsNatural and experimentalLowNo (possible some cases)No
Cats (domestic)Natural and experimentalHighYes (none to very mild in some cases)Yes, between cats
Tigers and lionsNaturalHighYesYes, between animals
FerretsExperimentalHighNo (mild in some cases)Yes, between ferrets
Minks (American minks, Neovison vison)NaturalHighYesYes, between minks and suggested from minks to humans
Egyptian fruit bats (Rousettus aegyptiacus)ExperimentalHighNoYes, between fruit bats
Golden Syrian HamstersExperimentalHighYes (none to very mild in some cases)Yes, between hamsters
Macaques (Macaca fascicularis and Macaca mulatta)ExperimentalHighYesYes

This review article provides a brief overview of animal coronaviruses and the veterinary experience of dealing with them. The authors note that there is extensive knowledge in veterinary medicine about animal coronaviruses, their evolution and pathobiology. They provide brief details of the major veterinary coronaviruses, such as Infectious Bronchitis Virus (IBV) of poultry and Feline Infectious Peritonitis Virus (FIPV) which have been known since the early 1900s, and provide examples on how coronaviruses can evolve, changing their tissue tropism and virulence. The authors use as an example the

Transmissible Gastro-Enteritis Virus of pigs (TGEV), which likely originated from the closely related canine coronavirus (CCoV), and in turn gave rise to the less virulent Porcine Respiratory Coronavirus (PRCoV).

The authors note that while animal models may be useful in developing human SARS-CoV-2 vaccines, there may also be lessons to be learned from experience using veterinary vaccines such as those for IBV and CCoV. In these cases, parentally administered vaccines against respiratory coronaviruses have been found to reduce the severity of respiratory signs, but not give full protection against respiratory infection or virulent virus, noting that prevention of infection may be more dependent on mucosal immunity.

Also discussed is the issue of antibody-dependent enhancement, which was found to cause a more severe disease in cats immunised against Feline Infectious Peritonitis Virus (FIPV) than in control cats.
A more positive lesson from the management of FIP relates to recent attempts to control FIP using two promising antiviral classes, namely protease inhibitors and nucleoside analogues, such as GS-441524, which is similar to the adenosine nucleoside monophosphate prodrug GS-5734; GS-5734 is the active molecule of Remdesivir.

The authors conclude that given the long-term experience gained with animal coronaviruses, veterinary medicine could help to forge a better understanding of the origin and spread of SARS-CoV-2 and guide future research in human medicine towards the development of immunogenic and safe vaccines and effective antiviral drug.

The review looked at the evidence available to answer two questions

Question 1: “What is the evidence that domestic animals (cats, ferrets, dogs, swine, cattle, sheep, goats, poultry, horses) can be infected with, or shed, the human-associated coronaviruses SARS-CoV, MERS-CoV, and SARS-CoV-2, which are associated with the diseases, SARS, MERS, and COVID-19, respectively?”

Question 2: “What is the evidence that domestic animals (cats, ferrets, dogs, swine, cattle, sheep, goats, poultry, horses) can act as a fomite for the human-associated coronaviruses SARS-CoV, MERS- CoV, and SARS-CoV-2, which are associated with the diseases, SARS, MERS, and COVID-19, respectively?

The review includes case studies and early experimental and epidemiological studies as well as studies of related coronaviruses (SARS and MERS).

They concluded that from the evidence reviewed (to 29th April 2020):

The authors acknowledge that there are many questions unanswered and state that they see this as a living review which will be updated as new evidence becomes available.

It should be noted that while this is described as a “systematic review”, this review of the published literature was undertaken rapidly in response to the current pandemic and has not been peer-reviewed.

Impact of the pandemic

There are now a number of articles and surveys being published on the impact of the COVID pandemic on veterinary practice, animal ownership and animal welfare. Links, and a brief description of each of these papers, are provided below:

Veterinary practice

Companion animals

Horses

Report on the economic impact of the pandemic on the horse show industry in the United States.

This paper reviews published equine welfare research to compare the ways in which human lockdown reflects standard equine management

This paper reports on qualitative research carried out to investigate the implications of COVID lockdown policies on equine management and welfare with a focus on horses and ponies at risk of laminitis and obesity.

One welfare

This paper uses the One Welfare Framework to provide an overview, of the impact of the pandemic on animal welfare, human welfare and the environment.

This paper reports on large survey of pet owners (n= 5926) in the UK and reported on the role of relationships and interactions between humans and animals, and the impact on mental health, during the early stages of the Covid pandemic (April – June 2020)

About evidence collections

Evidence collections bring together collections of published papers on topics of interest and importance to the veterinary professions. Papers are chosen for relevance and accessibility, with the full text of articles either being available through the RCVS Knowledge library, on open access or from other publications to which a significant number of veterinary professionals are likely to have access. This means that there may be relevant evidence that is not included.

If you would like assistance in searching for further evidence on this topic you may find the following helpful EBVM Toolkit 2: Finding the best available evidence.

If you would like to suggest a paper for inclusion in one of our published evidence collections, or a topic for a future collection, please email library@rcvsknowledge.org

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