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Updated on June 11, 2020
SARS-CoV-2 in pets
PETS DO NOT APPEAR TO BE EASILY INFECTED WITH SARS-COV-2
During the first five months of the COVID-19 outbreak (January 1 – June 8, 2020), which includes the first twelve weeks following the March 11 declaration by the WHO of a global pandemic, fewer than 20 pets have tested positive, with confirmation, for SARS-CoV-2 globally. This despite the fact that as of June 8, the number of people confirmed with COVID-19 exceeded 7 million globally and 1.9 million in the United States.
There have been fewer than 25 reports from around the world of pets (dogs and cats) being infected with SARS-CoV-2; however, none of these reports suggest that pets are a source of infection for people. Evidence to date from the few domestic animals that have tested positive for SARS-CoV-2 indicate these infections are typically a result of close contact with people with COVID-19. In laboratory studies of experimental infection with SARS-CoV-2, ferrets, Syrian hamsters, and cats—all animals that may be kept as pets—show potential for serving as animal models of human infection, but dogs, pigs, chickens, and ducks do not. And, although molecular modeling and in vitro studies suggest that multiple animal species may theoretically be able to be infected with SARS-CoV-2, a definitive intermediate host has not been identified. There is little to no evidence that domestic animals are easily infected with SARS-CoV-2 under natural conditions and no evidence to date that they transmit the virus to people. The primary mode of transmission of COVID-19 in humans is person-to-person spread.
Additional evidence that pets appear to be only rarely infected with SARS-CoV-2 under natural conditions comes from two commercial laboratories in the United States, which in April 2020 announced the availability of a reverse transcriptase polymerase chain reaction (RT-PCR) test for SARS-CoV-2 in domestic animals, including cats and dogs. During development and validation of these tests, each laboratory assessed thousands of specimens from dogs and cats for the COVID-19 virus without obtaining any positive results. Those specimens came from pets located in the United States, South Korea, Canada, and Europe, including regions that were concurrently experiencing a high number of human COVID-19 cases. While this is encouraging, the specimens tested were originally submitted for PCR analysis of more common pathogens that cause respiratory disease in dogs and cats and, as such, per-case information as to whether these pets had contact with suspected or confirmed COVID-19 positive people is not available.
The first confirmed reports of pets infected with SARS-CoV-2 came from Hong Kong. Since the onset of the outbreak there, government officials with the Agriculture, Fisheries, and Conservation Department (AFCD) recommended that mammalian pets from households with persons hospitalized because of COVID-19 be cared for in quarantine and tested for infection with SARS-CoV-2. As of April 15, 30 dogs, 17 cats, and two hamsters had been held at the AFCD quarantine facility. However, only two dogs and one cat have tested positive for SARS-CoV-2 infection. Infection was confirmed by detection and sequencing of viral RNA in upper respiratory tract samples and detection of neutralizing antibodies against the virus in serum. Virus also was isolated from one of the two infected dogs. None of the animals in quarantine, including the three positive pets, developed clinical signs of respiratory disease and all positive animals were released from quarantine after at least a 14-day stay and negative RT-PCR test results on samples collected over at least two consecutive days. On May 14, an article describing SARS-CoV-2 infection in the two Hong Kong dogs was published online in Nature.
The first reports of positive pets in the United States came on April 22 when the CDC and National Veterinary Services Laboratories (NVSL) reported that two cats in New York state were confirmed to be infected with SARS-CoV-2. Both cats had signs of mild respiratory illness and were expected to make a full recovery. The owner of one of these cats was confirmed to have had COVID-19; a second cat living in this same household tested negative for the virus. The second positive cat was an indoor-outdoor cat whose owner had no symptoms of COVID-19 and was never tested. However, it lived in an area with a high number of human COVID-19 cases. It was presumed that that this cat was infected by either its owner, who was asymptomatically infected with SARS-CoV-2, or by another infected person in the neighborhood. A case report describing clinical signs and progression in these two cats and diagnostic tests completed was published in the June 8, 2020 issue of the Morbidity and Mortality Weekly Report. Until June 1, these are the only two positive pets confirmed to be infected in the United States.
On June 2, the USDA NVSL announced the first confirmed case of SARS-CoV-2 in a dog in the United States. This pet, a German Shepherd Dog, lived with one other dog and their two owners in New York state. One of the dogs’ owners had tested positive for, and the second had symptoms consistent with, COVID-19 prior to the German Shepherd Dog developing signs of respiratory illness. The second dog in the household remained apparently healthy. Samples taken from the affected German Shepherd Dog tested presumptive positive for SARS-CoV-2 by use of RT-PCR performed at a private veterinary laboratory, which then reported its results to state and federal officials. Results of further laboratory tests performed at the NVSL on the original and additional samples collected from the German Shepherd Dog confirmed that this dog was infected with SARS-CoV-2. The dog was presumed to have been infected by its owners and is expected to make a full recovery. Results of serological tests conducted by the NVSL on the second dog in the household revealed virus-specific antibodies, indicating that although this dog never developed clinical signs of disease, it had been exposed to the COVID-19 virus.
An in-depth summary of these and other reported cases of naturally occurring SARS-CoV-2 infection in animals is available for those who wish to learn more. It will be updated regularly, so we encourage you to check back often.
Because infection of animals with SARS-CoV-2 meets the World Organisation for Animal Health (OIE) criteria of an emerging disease, any confirmed infection should be reported to the OIE in accordance with the Terrestrial Animal Health Code. Both the US and Hong Kong governments have reported the positive animals described above to the OIE. In addition, all cases of SARS-CoV-2 in animals within the USA that are confirmed by testing conducted at the NVSL will be posted on the USDA/APHIS Web site.
Because infection of animals with SARS-CoV-2 meets the World Organisation for Animal Health (OIE) criteria of an emerging disease, any confirmed infection should be reported to the OIE in accordance with the Terrestrial Animal Health Code. Both the US and Hong Kong governments have reported the five positive animals described above to the OIE.
Information about testing for SARS-CoV-2 in animals is available here.
KEEPING PETS SAFE DURING THE PANDEMIC
For pet owners, preparing in advance is key. Make sure you have an emergency kit prepared, with at least two weeks’ worth of your pet’s food and any needed medications. Usually we think about emergency kits like this in terms of what might be needed for an evacuation, but it’s also good to have one prepared in the case of quarantine or self-isolation when you cannot leave your home.
Other appropriate practices include not letting pets interact with people or other animals outside the household; keeping cats indoors, if possible, to prevent them from interacting with other animals or people; walking dogs on a leash, maintaining at least 6 feet from other people and animals; and avoiding dog parks or public places where a large number of people and dogs gather.
If you are ill with COVID-19 (either suspected or confirmed with a test), restrict contact with your pets and other animals, just like you would with other people; have another member of your household care for your pets while you are sick; avoid contact with your pet, including petting, snuggling, being kissed or licked, and sharing food or bedding. If you must care for your pet or be around animals while you are sick, wear a cloth face covering and wash your hands before and after you interact with them. You should not share dishes, drinking glasses, cups, eating utensils, towels, or bedding with other people or pets in your home. Additional guidance on managing pets in homes where people are sick with COVID-19 is available from the CDC.
While we are recommending these as good practices, it is important to remember that there is no evidence at this time that animals play a significant role in spreading SARS-CoV-2. Based on the limited information available to date, the risk of animals spreading COVID-19 to people is considered to be low. Accordingly, there is no reason to remove pets from homes where COVID-19 has been identified in members of the household, unless there is risk that the pet itself is not able to be cared for appropriately. In this pandemic emergency, pets and people each need the support of the other and veterinarians are there to support the good health of both.
SARS-CoV-2 in other species
TIGER AND LIONS IN BRONX ZOO, NEW YORK, UNITED STATES
On April 5, the USDA National Veterinary Services Laboratories announced a positive finding of SARS-CoV-2 in samples from one tiger at the Bronx Zoo in New York City. USDA reported results of the positive test to the OIE on April 6.
The tiger was one of five tigers and three lions housed in two enclosures at the zoo. Four of these tigers and all of the lions had developed clinical signs of mild respiratory disease over the course of a week. The affected animals are long-term residents of the zoo, without chronic medical conditions, and no new animals have been introduced to the groups for several years. As such, it was presumed that the other large cats with clinical signs of respiratory disease were also infected with SARS-CoV-2. The source of infection was presumed to be transmission from a zookeeper, who at the time of exposure had not yet developed symptoms of COVID-19.
On April 22, the Wildlife Conservation Society (WCS) published an update on the tigers and lions at its Bronx Zoo. The zoo’s laboratory partners had developed a fecal sample test that allowed the other large cats to be tested without the need for general anesthesia. The zoo tested all of the tigers and lions described in the initial report except for the original positive tiger. Results from these 7 animals were positive, suggesting that the 8 large cats described in the initial report were all likely to have been infected with SARS-CoV-2. The WCS also reported that the 4 tigers and 3 lions that initially developed clinical signs of respiratory disease were recovering well. Animals in other parts of the zoo, including other large cats, never developed clinical signs of disease. Enhanced biosecurity protocols have been implemented for staff caring for nondomestic felids in the four zoos overseen by the WCS.
FARMED MINK IN THE NETHERLANDS
On April 26, the Dutch Minister of Agriculture, Nature, and Food Quality issued a letter to the Dutch parliament reporting that several mink on each of two large farms had tested positive for SARS-CoV-2. The first of these farms comprised two closely situated locations housing mink, whereas at the second farm all mink were housed in a single location. Each farm had noted an increased incidence of gastrointestinal and respiratory disease and overall mortality in the animals. Several animal caretakers at each farm had developed symptoms consistent with COVID-19. It is believed that these caretakers transmitted the virus to the mink. Plans were in place to conduct additional testing of other mink, both sick and healthy, and air and dust samples from each farm for SARS-CoV-2. All Dutch mink farmers, veterinarians, and researchers were also notified of the new requirement to report any respiratory problems or increased mortality in mink. In addition, all employees were advised to wear personal protective equipment when working with or caring for the mink. As an additional precautionary measure, the Dutch public health agency advised people against cycling or walking within a radius of approximately 400 meters around each infected farm until the results from tests on the air and dust samples were known. This ban was lifted when results indicated that air and dust outside the barns housing the mink did not contain SARS-CoV-2.
On May 8, the Minister reported that SARS-CoV-2 had been detected in mink from two additional farms, bringing the total of infected mink farms in the Netherlands to four. Human safety and health precautions put into place for the first two infected farms were implemented on the second set of infected farms. Ongoing studies of SARS-CoV-2 in mink will include samples from all four farms.
On May 25, the Minister reported that based on initial sequence analyses and phylogenetic mapping, it was plausible that in at least two cases, the virus was transmitted from an infected mink to a susceptible human host. More research is being done to better understand whether mink-to-human transmission of SARS-CoV-2 can take place. Additionally, seven of 24 farm cats were found to have circulating antibodies specific for SARS-CoV-2, indicating they had been infected with the virus. Viral RNA was detected in one of the seven seropositive cats, but at such a low copy number that genomic sequencing was not possible. It is not yet known what role, if any, the cats play in transmission of the virus. Additional studies are ongoing.
On June 1, four additional infected farms were identified through use of the early warning surveillance plan that requires all farmers to submit carcasses each week of any mink that died naturally to test for SARS-CoV-2 by use of necropsy and RT-PCR.
On June 3, the Minister of Agriculture, Nature, and Food Quality and the Minister of Health, Welfare, and Sport made a decision, based on risk to animal health and potential risk to public health, that mink on all current and future infected mink farms will be culled and owners compensated for their loss.
Studies on the infected mink farms and additional surveillance across all farms are ongoing and, as new results become available, information in our in-depth summary of reported cases of naturally occurring SARS-CoV-2 infection in animals will be updated accordingly.
Interpreting reports of naturally occurring SARS-CoV-2 infection in animals
We anticipate that as the COVID-19 pandemic continues, news and research articles will be published and reports circulated of additional animals, both domestic and wild, that are apparently infected with SARS-CoV-2. However, it is important to recognize that until confirmed, an initial positive RT-PCR test result may not mean that an animal is definitively infected with SARS-CoV-2; instead, depending on the sample tested, it may mean only that the animal picked up viral remnants via interaction with (e.g., licking) a SARS-CoV-2 contaminated environment or person with COVID-19. Confirmatory testing is needed to identify animals truly infected. In the United States, confirmed cases of SARS-CoV-2 infection in animals are tracked by the U.S. Department of Agriculture, Animal and Plant Health Inspection Service (USDA/APHIS). Globally, the OIE publishes confirmed reports of SARS-CoV-2 in animals that it receives from OIE Member Countries on the World Animal Health Information Database (WAHIS) Interface. We will also update our in-depth summary of reported cases of naturally occurring SARS-CoV-2 infection in animals on a regular basis, so we encourage you to check back often.
Neither the AVMA nor the CDC, USDA, American Association of Veterinary Laboratory Diagnosticians (AAVLD), National Association of State Public Health Veterinarians (NASPHV), or National Assembly of State Animal Health Officials recommend routine testing of animals for COVID-19. However, because the situation is ever-evolving, public and animal health officials may decide to test certain animals. In the United States, the decision to test should be made collaboratively between the attending veterinarian and local, state, and/or federal public health and animal health officials. More information about testing of veterinary patients for SARS-CoV-2 is available here.
Although testing of animals uses the same techniques as those used for humans, the NVSL and other laboratories incorporate animal-specific reagents to preserve needed supplies for testing of humans. Additional information on human testing is available on the Johns Hopkins University COVID-19 Testing Insights Initiative website, which was launched in late April 2020.
To aid in interpretation of test results that might be mentioned in reports of SARS-CoV-2 positive animals, we have summarized below three commonly used tests and what a positive result on each may mean. This is not meant to be an exhaustive list of potential SARS-CoV-2 tests that might be used for animals, nor a complete explanation of how each test is performed. It is meant only as an aid in critically reading news reports, scientific articles, and other information about SARS-CoV-2 in animals.
From the scientific literature on SARS-CoV-2 in non-human animals
Since the genome of the new SARS-CoV-2 was first sequenced in January 2020, many research studies have been completed by scientists around the world to better understand the virus’s origin, modes of transmission, and pathogenic mechanisms. Some studies are designed to find good animal models of SARS-CoV-2 infection, whereas others are being conducted to explore the potential host range of the virus. Similar studies were conducted after the SARS outbreak in 2003-2004. Those earlier studies of a different, but related, coronavirus led to findings that civet cats (a species distinct from domestic cats) may have been an intermediate host for the SARS-CoV virus; domestic cats and ferrets could be experimentally infected with the SARS-CoV virus and transmit it to naïve cats or ferrets, respectively, under experimental conditions; and a very few cats (< 10) and one dog belonging to owners with SARS that lived in a large apartment complex in Hong Kong with an extremely high number of human SARS cases tested positive for the SARS-CoV virus.
Results of more recent studies describing experimental infections of domestic animals with SARS-CoV-2 or exploring the potential host range of SARS-CoV-2 can also help veterinarians and other public health professionals better understand what role, if any, animals might play in the ongoing pandemic. Ferrets, Syrian hamsters, and cats—all animals that may be kept as pets—show early potential for serving as animal models of human infection with the COVID-19 virus, but dogs, pigs, chickens, and ducks do not. And, while comparative sequence analyses, molecular modeling and in vitro studies suggest that multiple animal species may theoretically be able to be infected with SARS-CoV-2, a definitive intermediate host has not yet been found. In addition, it is important to note that there is little to no evidence that domestic animals are easily infected with SARS-CoV-2 under natural conditions and no evidence that they can transmit the virus to people. The primary mode of transmission of COVID-19 in humans is person-to-person via respiratory droplets and contact.
Below, we provide a brief summary of three primary lines of investigation that have been used to study SARS-CoV-2 in animals and list some strengths and potential weaknesses of each. We have developed an in-depth summary of key research articles for those who wish to learn more and will update this summary on a regular basis. We also believe it is important to note that because of the rapid rate of research on SARS-CoV-2 and the need to learn as much as possible about the virus in order to develop new approaches to mitigate its pathogenicity and transmission rate, many research papers are being posted on preprint websites such as bioRxiv and medRxiv before being submitted for potential publication in a peer-reviewed journal. These open-access sites allow for rapid dissemination of information and wide sharing of experimental designs and preliminary results, which in turn allows for greater collaboration among scientists from around the world. However, it can also lead to results not yet reaffirmed or peer-reviewed being inadvertently publicized as definitive statements and conclusive evidence. Readers are encouraged to pay attention to the source of new information regarding COVID-19 and SARS-CoV-2 and heed disclaimers on non–peer-reviewed platforms. For example, the disclaimer on the bioRxiv website notes that papers posted are “preliminary reports and have not been peer-reviewed. They should not be regarded as conclusive, guide clinical practice/health-related behavior, or be reported in news media as established information.” A similar disclaimer is found on the medRxiv site.
COMPARATIVE SEQUENCE ANALYSES, MOLECULAR MODELING, AND IN VITRO STUDIES
Immediately after the SARS-CoV-2 genomic sequence was first described in January 2020, multiple laboratories began extensive comparisons of the new coronavirus sequence with known sequences of other coronaviruses. Results of these analyses helped map out the genomic and protein structure of SARS-CoV-2 and its evolutionary relationship with other coronaviruses. These comparisons revealed that although SARS-CoV-2 was a genetically distinct virus, it was most similar to two betacoronaviruses: one associated with bats, and the other the causative agent of the 2003-2004 severe acute respiratory syndrome (SARS) outbreak in humans—that is, SARS-CoV.
Additionally, using comparative sequence analyses of coronavirus surface proteins and molecular modeling techniques, SARS-CoV-2 was found to have a similar receptor-binding domain (RBD) on its surface spike protein to that on the spike protein of SARS-CoV. These similarities helped identify that the host receptor used by SARS-CoV to infect human cells—angiotensin-converting enzyme 2 (ACE2)—was also used by SARS-CoV-2. Binding of the RBDs on the viral spike protein to ACE2 on the surface of host cells is one of the necessary steps leading to replication and amplification of these two viruses in permissive hosts.
The protein sequence and structure of ACE2 is fairly conserved across mammalian species. However, changes from the human ACE2 sequence in one or more amino acids, particularly in the viral binding region of ACE2, can alter the binding affinity between SARS-CoV-2 and the host cell, making some animal species more permissive to infection than others. Molecular modeling coupled with in vitro studies can be have been used to analyze the interaction between the SARS-CoV-2 spike protein RBD and the viral binding region of ACE2 from a wide variety of animal species, with results indicating those species that, theoretically, should be most permissive to infection.
An advantage to using comparative sequence analyses, molecular modeling, and in vitro techniques is that live animals are not needed to study the interactions between viral surface proteins and surface proteins from multiple potential host species. Results can then be used to predict which interactions might be most important for viral infectivity, identify potential permissive non-human animal hosts for SARS-CoV-2, and help narrow down the choice of species to use in subsequent experimental infection and transmission studies. However, there are limitations to studies that use these techniques. In the example provided above, although the interaction between the SARS-CoV-2 spike protein and ACE2 on host cells may be necessary for the virus to infect a given species, it is not sufficient for infection. That is, there are numerous other virus-host interactions required for SARS-CoV-2 to enter and replicate effectively within host cells while evading the host immune system in order to amplify and spread as infectious viral particles to other members of the same host species. Thus, although results of comparative sequence analyses, molecular modeling, and in vitro studies may provide clues that can help identify permissive hosts for SARS-CoV-2, they should not be used to make definitive statements regarding the ability of SARS-CoV-2 to infect or be transmitted by a given animal species under natural—or even experimental—conditions.
EXPERIMENTAL INFECTION AND TRANSMISSION STUDIES
Experimental infection and transmission studies are used to develop animal models of human infection with SARS-CoV-2. Reliable animal models are needed for pathogenicity studies and studies that may ultimately lead to new anti-viral drugs and COVID-19 vaccines. Results of experimental infection and transmission studies may also help identify potential intermediate hosts in the evolution of the virus from its natural animal reservoir—likely a bat—to SARS-CoV-2, a betacoronavirus that preferentially infects and replicates in humans.
The species of animals used in these types of studies can be selected on the basis of what is known about similar viruses; information from comparative sequence analyses, molecular modeling, and in vitro studies as described above; and reports of animals, particularly pets, that may be, in rare situations, naturally infected with SARS-CoV-2 following close contact with a COVID-19 positive person.
Because the genomic sequence and structure of SARS-CoV-2 is similar to that of SARS-CoV and both viruses use the host ACE2 receptor to infect cells, animals known to be permissive to SARS-CoV under laboratory conditions—cats and ferrets—were two of the first animals used in recent experimental infection and transmission studies of SARS-CoV-2. These animals were also identified as potential permissive host species on the basis of comparative sequence analyses, molecular modeling, and in vitro studies, and although extremely rare, SARS-CoV-2 can be transmitted from infected owners to pet cats.
Positive results from multiple studies conducted in different laboratories suggest that cats and ferrets, as well as other domestic animals (e.g., Syrian hamsters) and non-human primates, can be infected with SARS-CoV-2 and transmit the virus to naïve animals under experimental conditions. The results of some of these studies have been widely publicized in the press, which has raised concern from pet owners. However, we emphasize caution in not overinterpreting the results from experimental infection and transmission studies, and also caution about extrapolating them to the potential for SARS-CoV-2 to naturally infect or be transmitted by companion animals kept as pets. Our rationale is as follows:
SEROLOGICAL SURVEYS OF ANIMAL POPULATIONS
Serological surveys may be conducted to determine whether animals living in areas with high numbers of human COVID-19 cases have been infected with SARS-CoV-2. In these studies, blood is collected from all animals in a given population, and serum analyzed for the presence of antibodies against SARS-CoV-2. Detection of antibodies is most commonly done via an enzyme-linked immunosorbent assay (ELISA), which can detect all antibodies against a specific surface viral peptide or protein, or a particular class of virus-specific antibodies such as IgM, which appears early in the host immune response, or more typically, IgG, which appears later and persists longer than does IgM. Serum can also be analyzed for virus neutralizing antibodies, although these assays are more time and resource intensive than are ELISAs.
A positive ELISA or virus neutralizing antibody result suggests that the animal was infected with SARS-CoV-2—and may still be infected—at a level and for a duration sufficient to elicit a virus-specific antibody response. A negative result may mean that the animal was never infected with SARS-CoV-2 or that it was only recently infected and has not yet mounted an immune response to the virus.
Thus, results of serological surveys can differentiate between animals that were infected with SARS-CoV-2 at a level sufficient to induce viral-specific antibody production from those that were not. However, serological surveys cannot be used to identify currently infected animals, nor can they be used to draw definitive conclusions regarding the course of infection in animals found to be seropositive—that is, the source, duration, and severity of infection. Perhaps most importantly, results of serological surveys cannot be used to draw definitive conclusions regarding the ability of a seropositive animal to transmit SARS-CoV-2 to other animals, including people.
To date, there is no conclusive evidence from published scientific studies that, under natural conditions, domestic animals, including those kept as pets such as cats, dogs, ferrets, and Syrian hamsters, can be readily infected with or transmit SARS-CoV-2. However, many additional studies are underway to better understand the transmission dynamics and pathogenic mechanisms of this virus, with results of multiple studies being posted or published online on an almost daily basis. To help veterinarians and other animal health professionals stay current with what is known about SARS-CoV-2 and domestic animals, an online rapid review of the literature has been conducted by the Systematic Reviews for Animals & Food organization. This rapid review was first posted on March 20, 2020 and has been updated multiple times since then. The AVMA regularly updates our COVID-19 website, including the in-depth summary of key research articles focused on SARS-CoV-2 in animals, to help ensure veterinarians have the best data available upon which to base clinical decisions and risk assessments. We encourage you to check back often.
SUMMARY AND CURRENT RECOMMENDATIONS
Despite the number of global cases of COVID-19 surpassing the 7 million mark as of June 8, 2020, we are aware of only a handful of pets and captive or farmed wild animals globally that have tested positive for SARS-CoV-2. In all cases, the source of the infection for pets was presumed to be one or more persons with confirmed or suspected COVID-19. At this point in time, there is also no evidence that domestic animals, including pets and livestock, play a significant role in spreading SARS-CoV-2 to people.
Therefore, the AVMA maintains its current recommendations regarding SARS-CoV-2 and animals. These recommendations, which are supported by guidance from the US Centers for Disease Control and Prevention (CDC) and World Organization for Animal Health (OIE), are that:
During this pandemic emergency, animals and people each need the support of the other and veterinarians are there to support the good health of both.