A 2021-2022 survey conducted in the United States reported that about 90.5 million households owned at least one pet, 23 million of which had acquired a pet during the first year of the coronavirus disease 2019 (COVID-19) pandemic.
Pet ownership is associated with numerous positive benefits for the owner, such as improved mental health. However, pet ownership can increase the risk of zoonotic disease transmission despite these advantages. To date, studies on zoonotic disease transmission in pets remain limited.
Study: Clinical and epidemiologic features of SARS-CoV-2 in dogs and cats compiled through national surveillance in the United States. Image Credit: Erik Lam / Shutterstock.com
Background
Like all other coronaviruses, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has a broad mammalian host range. The World Organization for Animal Health (WOAH) has reported SARS-CoV-2 infections in 35 countries from 14 mammalian families as of July 12, 2022.
The animals susceptible to COVID-19 have been divided into four groups according to their interaction with people. These include exotic animals, free-ranging wild animals, farmed animals, and companion animals.
Among these, companion animals have been reported to be the second most affected animal group, with approximately 60% of all reported animals infected with SARS-CoV-2 between February 29, 2020, and December 31, 2021, included in this category.
A new study published on the preprint server Research Square* analyzes the clinical and epidemiological features of SARS-CoV-2 infection in companion animals, particularly dogs and cats, in the United States.
About the study
The current study involved the identification of cases through active or passive surveillance of animals, following which samples were collected and sent to the United States Department of Agriculture (USDA) National Animal Health Laboratory Network (NAHLN) laboratories. A confirmatory test for SARS-CoV-2 was subsequently carried out by the USDA National Veterinary Services Laboratories (USDA-NVSL).
Information on the animals’ sex, age, species, comorbidities, clinical signs, and diagnostic tests were collected using the One Health Case Investigation Form for Animals developed by U.S. Centers for Disease Control and Prevention (CDC). This form was also used to obtain information on the person who was associated with the infection of the animal, dates of the positive test and symptom onset, as well as the frequency of interaction with the animal.
Clinical signs were categorized into three types based on which body systems were affected, of which included respiratory, gastrointestinal, and non-specific signs. For multi-pet households, the conditional probability was used to determine whether infection of one animal could lead to infection of another animal that lived in the same household.
Ct values and virus neutralization (VN) antibody titers were assessed to determine the immune response and timeline of infection for companion animals. Finally, a cross-correlation time series analysis was performed to determine whether an increase in COVID-19 among people also led to an increase in infection among companion animals.
Study findings
A total of 345 animals from 33 U.S. states tested positive for SARS-CoV-2. Of these, 204 were companion animals, including 95 dogs and 109 cats.
Taken together, 94% of SARS-CoV-2-positive animals were exposed to an individual who also tested positive for SARS-CoV-2. The source was unknown for 6% of companion animals.
About 48% of these animals exhibited clinical signs similar to human SARS-CoV-2 infection, while 52% did not experience any symptoms during sampling. Respiratory symptoms were most frequently reported, followed by non-specific and gastrointestinal symptoms.
Clinical signs varied depending on the species of cat. Lethargy and sneezing were most commonly reported in cats, while cough and lethargy were most commonly reported in dogs. Overall, cats were more clinically ill as compared to dogs.
A total of 36 households had more than one dog or cat. The probability of infection of a second pet due to infection of the first animal was 25%. Additionally, the probability was higher if a cat was the index pet.
The average Ct value was 28.6, whereas VN titers ranged from eight to 512 for all SARS-CoV-2-positive companion animals. Ct values for nucleic acid detection peaked on days five and six for dogs and cats, respectively.
Detection of SARS-CoV-2 occurred for up to 13 and 23 days in dogs and cats, respectively. Virus-specific antibodies were detected five and three days following nucleic acid detection in cats and dogs, respectively.
Along with the early-circulating variant, the SARS-CoV-2 Delta, Alpha, Iota, and Epsilon variants were also detected among 70 animals, with Delta being the most commonly detected variant.
The median number of days between the onset of symptoms in humans and companion animals was six and ten days in dogs and cats, respectively. The median duration of clinical infection was 16.5 and 10 days in dogs and cats, respectively.
Whether the increase in human infections also led to an increase in infections among companion animals remains unclear.
Conclusions
The current study demonstrated that zoonotic disease transmission from humans to companion animals, especially dogs and cats, is possible. The impact of SARS-CoV-2 infection was higher in cats as compared to dogs. SARS-CoV-2 transmission from one pet to another was also observed.
These observations can be helpful for both the animal and public health sectors in managing the COVID-19 pandemic. Further developments in the One Health collaboration mechanisms are needed to protect animal and human health from COVID-19, as well as future threats of zoonotic diseases.
Limitations
The surveillance used in the study varied based on different jurisdictions, which makes the reporting of cases variable. Additionally, the sample size of the study was small.
The current study also did not include households where several people may have caused companion animal infections. Finally, the study did not extend to the Omicron period; therefore, the impact of this variant on companion animals remains unknown.
*Important notice
Research Square publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
