Clinical and epidemiological features of SARS-CoV-2 in companion animals

In a recent study posted to the Research Square* preprint server, researchers examined the clinical and epidemiological features of coronavirus disease 2019 (COVID-19) in dogs and cats.

Numerous beneficial effects of pet ownership, including mental health benefits, have been scientifically established. Companion animals account for 60% of all animals reported to the World Organization for Animal Health (WOAH) between February 29, 2020 and December 31, 2021 worldwide, making them the second most reported animal group infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to farmed mink. However, at the national and international level, there are limited surveillance efforts to identify the transmission of zoonotic pathogens, such as SARS-CoV-2, in companion animals.

​​​​​​​Study: Clinical and epidemiological features of SARS-CoV-2 in dogs and cats collected through national surveillance in the United States. ​​​​​​​Image Credit: Lindsay Helms/Shutterstock

About the study

In the current study, researchers from the US Centers for Disease Control and Prevention (CDC), the US Department of Agriculture (USDA), and Texas A&M University described the clinical and epidemiological features of SARS-CoV-2 in US companion animals that are discovered through both passive and active surveillance.

Animal SARS-CoV-2 cases are detected in the US through passive or aggressive surveillance. For example, when pet owners take their companion animals to veterinary clinics or hospitals, case identification is often initiated through passive monitoring. Samples are then sent to various veterinary diagnostic labs for SARS-CoV-2 testing. In addition, animals with known SARS-CoV-2 exposure or clinical signs indicative of SARS-CoV-2 infection are actively sought by health officials or researchers through active surveillance. These include joint One Health studies of SARS-CoV2 transmission in households, zoos, animal shelters, animal rescues, animal rehabilitation facilities and veterinary clinics involving both humans and animals.

According to the US case definition, an animal has been determined to be SARS-CoV-2 positive at the US Department of Agriculture’s National Veterinary Services Laboratories (USDA-NVSL) if one of the following conditions is met: (1) the SARS- CoV-2 sequence was generated directly from a suspected or suspected positive animal specimen or indirectly from a viral isolate obtained from that animal, or (2) serological sample from a suspected or suspected positive animal showed the presence of SARS-CoV-2 neutralizing antibody to .

All dog and cat samples meeting the following requirements were required to be submitted to the USDA-NVSL: (1) strong sequencing candidates with SARS-CoV-2 real-time reverse transcription polymerase chain reaction (RT-PCR) cycle threshold (Ct) values ​​smaller than 30; (2) linked to unusual morbidity and mortality; or (3) suspected or known to be infected with SARS-CoV-2 variants, including Alpha, Delta and Omicron variants.

Based on the body systems affected, the researchers divided the clinical indicators into three categories: respiratory symptoms including cough, shortness of breath, difficulty breathing, sneezing, runny nose and eye discharge, gastrointestinal symptoms including vomiting and diarrhea, and nonspecific symptoms such as lethargy, loss of appetite, fever). In addition, ct levels and virus neutralization (VN) titers were measured after exposure to a person infected with COVID-19 to understand the timeline of infection and immune response of companion animals infected with SARS-CoV-2.

Results of the SARS-CoV-2 RT-PCR and SARS-CoV-2 VN titers were compared to those observed at the putative exposure date. The geometric mean titer and lowest Ct values ​​of oral and nasal swabs were calculated every two days. For animals confirmed to be infected with COVID-19, mean Ct values ​​and log transformed geometric mean titers of viral neutralizing antibodies were determined.

Results

About 345 animals observed in 33 states in the US tested positive for SARS-CoV-2 between March 2020 and December 2021. Nearly 59% of them, including 109 cats and 95 dogs, were companion animals, while 94% of the cases detected were companion animals by passive surveillance involved first contact with a COVID-19 positive person.

Clinical signs reported in cats (n=55; A) and dogs (n=42; B).  Of 97 animals with clinical signs, the proportion of each clinical sign displayed within each species is shown.  Since a given animal may exhibit multiple clinical signs, percentages are calculated based on the number of characters displayed, not individual animals.

Clinical signs reported in cats (n=55; A) and dogs (n=42; B). Of 97 animals with clinical signs, the proportion of each clinical sign displayed within each species is shown. Since a given animal may exhibit multiple clinical signs, percentages are calculated based on the number of characters displayed, not individual animals.

The study results showed that 52% of the companion animals had no documented clinical indications at the time of sampling, while 48% had clinical signs consistent with SARS-CoV-2 infection. This differed significantly depending on the type of surveillance used; while 72% of animals detected through passive surveillance showed clinical signs, only 27% of animals discovered through active surveillance reported signs.

Animals showing clinical signs were most typically reported to have respiratory symptoms as compared to nonspecific and gastrointestinal symptoms. Of the animals with clinical signs, 21% and 16% of the cats experienced sneezing and lethargy, while 16% and 20% of the dogs experienced coughing and lethargy, respectively.

Of the 204 confirmed COVID-19 positive companion animals, 45% tested positive by VN alone, 33% by RT-PCR alone, and 23% by both VN and RT-PCR. For all companion animals tested positive by RT-PCR data, the mean Ct value was 28.6. All confirmed COVID-19 positive companion animals had median VN titres of 64, ranging from 8 to 512. Of these, the titers of dogs ranged between 8 and 128 with a median titer of 32, while those of cats ranged from 32 to 512 with a median titer of 32. median titre of 128.

Conclusion

The study results showed that companion animals such as dogs and cats are infected with SARS-CoV-2 after exposure to a COVID-19-infected person who often owns them. Therefore, case studies and surveillance involving both humans and animals are essential to understand the transmission and viral development of zoonotic diseases such as SARS-CoV-2.

*Important announcement

Research Square publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, should guide clinical practice/health-related behavior or be treated as established information.

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