Study indicates interspecies transmission of SARS-CoV-2 between humans and their pets occurs regularly
In a recent study published in the Viruses Journal, researchers assessed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroprevalence among domestic dogs and cats in households with SARS-CoV-2-positive humans in Germany.
Study: SARS-CoV-2 Infection and Clinical Signs in Cats and Dogs from Confirmed Positive Households in Germany. Image Credit: Chendongshan/Shutterstock.com
Globally, SARS-CoV-2 infections are serious public health concerns for humans and their pets. The contribution of animals in the source, spread, and evolution of the coronavirus disease 2019 (COVID-19)-causing organism, SARS-CoV-2, is debatable, particularly concerning domestic dogs (Canis lupus familiaris) and cats (Felis catus), since they are critical components of many human lives.
Studies have reported COVID-19 occurrence in dogs and cats; however, data on the role of pet animals in the dynamics of SARS-CoV-2 transmission are limited.
About the study
In the present study, researchers evaluated COVID-19 prevalence among cats and dogs in German households with SARS-CoV-2-positive household contacts. They also analyzed risk factors for SARS-CoV-2 transmission between humans and animals and COVID-19 symptomatology in domestic animals.
The analysis was performed to obtain data on the impact, occurrence, and consequences of SARS-CoV-2 infection in dogs and cats living with infected humans whose COVID-19 diagnosis was confirmed by polymerase chain reaction (PCR) between September and December 2021. This was during the SARS-CoV-2 Delta variant of concern (VOC) predominance period.
The study participants were required to have ≥1.0 cases of PCR-confirmed COVID-19 among household members in the three months before sampling and ≥1.0 pets (dogs or cats) showing a willingness to participate.
Serological samples were obtained from all animals to assess anti-SARS-CoV-2 spike (S) protein receptor-binding domain (RBD) antibody titers using enzyme-linked immunosorbent assays (ELISA).
The serological findings were analyzed with data obtained via questionnaires (for general information, human-animal interactions, and clinical symptomatology) filled out by the pet owners. Multivariate logistic regression modeling was performed for the analysis, and the odds ratios (OR) were calculated.
The team garnered support from the Chambers of Veterinarians in all federal states of Germany to alert veterinary clinics and online platforms, including homepages and social media. Individuals were appointed after four weeks of PCR-confirmed SARS-CoV-2 infection in ≥1.0 humans of the household. However, a period between three weeks and three months was permitted.
In total, 170 and 115 dogs and cats, respectively, from 177 households participated in the study; 50% (n=143) tested SARS-CoV-2-positive using ELISA, 42% (n=48) of cat serological samples and 56% (n=95) of dog serological samples tested SARS-CoV-2-positive. The actual SARS-CoV-2 seroprevalence rates for dogs and cats were 43% and 57%, respectively. The determined seroprevalence for dogs was greater than that in cats (OR 1.8) but not statistically significant.
The count of SARS-CoV-2-infected households and a greater-than-average intensity of human contact significantly increased COVID-19 risk for cats, whereas human contact beyond households protected cats against COVID-19.
Contrastingly, for dogs, contact beyond the household increased the risk of infection and lowered contact after established human infection, significantly protecting against COVID-19. No statistically significant associations existed between the documented COVID-19 symptomatology in the pets and their serological status.
At least 1.0 SARS-CoV-2-infected humans per household were significantly associated with the likelihood of cats developing anti-SARS-CoV-2 antibody titers (OR 3.1). The univariate analysis showed a lower likelihood for seropositive cats to have unsupervised outdoor access (OR 0.5) or human contact beyond households (OR 0.3) and greater intensity of contact with the owners (OR 2.3).
Dogs having anti-SARS-CoV-2 antibodies showed a greater likelihood of human contact beyond households (OR 2.0), and the dog owners showed a lower likelihood of stopping or reducing contact in the quarantine period (OR 0.5) and that >1.0 humans in the households were infected (OR 2.2).
Among households having >1.0 participating animals, seropositive pets showed a significantly greater likelihood of having another animal infected by SARS-CoV-2 in the households compared to seronegative ones (OR 9.6). In the multivariate analysis, more infected humans in the households were significantly associated with the probability of a cat being seropositive (OR 2.0).
Cats with SARS-CoV-2 seropositivity had a significantly greater likelihood of having more than average intensity of contact with owners (OR 2.5). Dogs showed a significantly lower likelihood of turning seropositive when owners reduce contact with them in the quarantine period (OR 0.5).
Dogs having SARS-CoV-2 seropositivity showed a significantly greater likelihood of human contact beyond households (OR 2.1). Of 119 pets showing COVID-19 signs, 22, 96, and 59 experienced them before, during, and after quarantine, respectively.
The most prevalent symptoms were increased rest requirements (19%), diarrhea (16%), decreased appetite (13%), nasal discharge (10%), coughing (nine percent), labored breathing (seven percent), and decreased resilience (seven percent).
Among 17% of animals, other symptoms included sneezing (eight percent). Of 119 animals showing clinical signs, 26% experienced degraded health, 22% experienced respiratory, and 17% experienced gastrointestinal symptoms.
Overall, the study findings, including only pets of SARS-CoV-2-infected households, showed a remarkably high seroprevalence rate for infected cats (42%) and an even higher rate for dogs (56%). Indicating that natural inter-species transmission of SARS-CoV-2 between human beings and their pets occurs regularly.
The greater seroprevalence among dogs could be due to greater contact intensity with humans. Moreover, the susceptibility of dogs and cats might vary with the SARS-CoV-2 variant.
The findings indicated that SARS-CoV-2-infected dogs and cats do not usually develop an illness resembling COVID-19 in humans. The frequency and intensity of human and pet contact influenced the risk of COVID-19 in pets.
Thus, basic-level hygiene measures must be followed during interactions with dogs and cats during COVID-19 to prevent mutual SARS-CoV-2 infections.