A 2021-2022 survey conducted in the United States found that about 90.5 million households owned at least one pet, of which 23 million had acquired a pet in the first year of the 2019 coronavirus disease (COVID-19) pandemic.
Keeping pets comes with numerous positive benefits for the owner, such as: B. Improved mental health. However, despite these benefits, keeping pets can increase the risk of zoonotic disease transmission. So far, there are only a few studies on the transmission of zoonotic diseases in domestic animals.
To learn: Clinical and epidemiological characteristics of SARS-CoV-2 in dogs and cats compiled by national surveillance in the United States. Photo credit: Erik Lam / Shutterstock.com
Like all other coronaviruses, 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 were divided into four groups based on their interactions with humans. These include exotic animals, free-roaming wild animals, farm animals and companion animals.
Among these, pets have been reported to be the second most affected group of animals, with approximately 60% of all reported animals infected with SARS-CoV-2 between February 29, 2020 and December 31, 2021 falling into this category.
A new study published on the preprint server research place* analyzes the clinical and epidemiological features of SARS-CoV-2 infection in domestic animals, particularly dogs and cats, in the United States.
About the study
The current study involved identifying cases through active or passive monitoring of animals, after 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 then performed by the USDA National Veterinary Services Laboratories (USDA-NVSL).
Information on the animals’ sex, age, species, comorbidities, clinical signs, and diagnostic tests was collected using the One Health Case Investigation Form for Animals developed by the US Centers for Disease Control and Prevention (CDC). This form was also used to obtain information about the person associated with infecting the animal, dates of positive testing and symptom onset, and frequency of interaction with the animal.
Clinical signs were classified into three types based on which body systems were affected, including respiratory, gastrointestinal, and non-specific signs. In households with multiple pets, conditional probability was used to determine whether infection of one animal could result in infection of another animal living in the same household.
Virus neutralization (VN) Ct values and antibody titers were evaluated to determine the immune response and time course of infection in companion animals. Finally, a cross-correlation time-series analysis was performed to determine whether an increase in COVID-19 in humans also led to an increase in infections in pets.
A total of 345 animals from 33 US 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 a person who also tested positive for SARS-CoV-2. The source was unknown for 6% of the pets.
Approximately 48% of these animals showed clinical symptoms similar to human SARS-CoV-2 infection, while 52% had no symptoms during sampling. Respiratory symptoms were reported most frequently, followed by non-specific and gastrointestinal symptoms.
The clinical signs varied according to the species of cat. Lethargy and sneezing were most commonly reported in cats, while coughing and lethargy were most commonly reported in dogs. Overall, cats were clinically more ill 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%. Also, the odds were higher when a cat was the index pet.
The average Ct value was 28.6, while VN titers ranged from eight to 512 in all SARS-CoV-2 positive pets. Ct values for nucleic acid detection peaked on days five and six in dogs and cats, respectively.
SARS-CoV-2 was detected for up to 13 or 23 days in dogs or cats. Virus-specific antibodies were detected five and three days after nucleic acid detection in cats and dogs, respectively.
In addition to the early circulating variant, the SARS-CoV-2 variants delta, alpha, iota and epsilon were also detected in 70 animals, with delta being the most frequently detected variant.
The median number of days between onset of symptoms in humans and pets 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 in domestic animals remains unclear.
The current study has shown that transmission of zoonotic diseases from humans to pets, especially dogs and cats, is possible. The effects of SARS-CoV-2 infection were higher in cats than in dogs. Transmission of SARS-CoV-2 from one pet to another has also been observed.
These observations can help both the animal health sector and the public health sector in managing the COVID-19 pandemic. Further developments in the One Health cooperation mechanisms are needed to protect human and animal health from COVID-19 and future zoonotic disease threats.
The surveillance used in the study varied by jurisdiction, making the reporting of cases different. In addition, the sample size of the study was small.
The current study also did not include households where multiple people may have caused pet infections. Finally, the study did not extend to the Omicron period; therefore, the effects of this variant on pets remain unknown.
research place publishes preliminary scientific reports that have not been peer-reviewed and therefore should not be considered conclusive, guide clinical practice/health behavior or treated as established information.