A recent study published in Research in veterinary sciences assessed the possible association of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) burden in owners infected with SARS-CoV-2 in their pet dogs.
Although SARS-CoV-2 is a human infection, studies have reported its cases even in domestic animal species, including dogs and cats. From Morais et al. found that SARS-CoV-2 infection in dogs with or without clinical symptoms was associated with close interaction with the owner (eg, kissing dogs or sleeping in the same bed). However, dogs are not as susceptible to infection even when exposed to humans infected with SARS-CoV-2.
About the study
As part of the multicenter study, researchers in the current study assessed the potential association of owner viral load with SARS-CoV-2 in dogs. They examined 20 SARS-CoV-2-positive pet owners from 13 families in Curitiba, Brazil, between October 2020 and June 2021. These dog owners tested SARS-CoV-2-positive by quantitative chain reaction reverse transcription-polymerase (RT-qPCR) assay.
The team gave an epidemiological questionnaire to all dog owners. A certified veterinarian collected oropharyngeal and rectal swabs from all dogs. He also took their blood samples for serological testing on day zero of the study and after seven days.
The researchers used a pre-specified probe-based genotyping system developed by Vogels et al. for further investigation of SARS-CoV-2 positive canine outbreaks. This helped them distinguish between infections with B.1.1.7, B.1.351, P.1, wild-type, and other lineages of SARS-CoV-2 using a dropout pattern for the spike (S) Δ69–70 and open reading frame 1a (Orf1a) Δ3675–3677 deletions as a result. In addition, the team used a magnetic bead enzyme immunoassay (ELISA) to check for the presence of immunoglobulin G (IgG) antibodies against SARS-CoV-2, nucleocapsid (N) and S proteins in RT-qPCR-positive dogs.
The team used dog blood samples obtained before the pandemic as a negative control. They established the threshold by calculating the mean of the pre-pandemic samples plus 3x the standard deviation. Finally, they used Fisher’s exact test to verify the association between positive and negative SARS-CoV-2 results in dogs and qualitative variables of the epidemiological questionnaire; and the Mann-Whitney test to compare these results. These tests considered a two-way significance level (α) of 5%.
The study presented the first five reports of natural SARS-CoV-2 infection in dogs notified to the Brazilian Ministry of Agriculture and the World Organization for Animal Health. Close contact with infected owners increased the likelihood of infection in dogs, especially with owners with a higher SARS-CoV-2 load. Most infections in pets were asymptomatic or resolved on their own, as shown in previous studies. However, in a rare case, a dog died because it had a pre-existing serious chronic respiratory disease. In other rare cases, dogs with no clinical history have also died, indicating that the outcome of SARS-CoV-2 infection varies widely in dogs, much like humans, and warrants investigation.
The cycle threshold (CJ) values reflecting viral load varied with the time of sample collection. Although SARS-CoV-2 ribonucleic acid (RNA) was detectable in dogs for up to 31 days after the first positive test, viruses can be detected weeks or months after symptoms resolve and remain undetected. infectious. Additionally, studies are yet to establish the role of the owner and the routes of transmission of infection from pets over time.
Lower susceptibility of dogs to SARS-CoV-2 infection explains why SARS-CoV-2 negative dogs of SARS-CoV-2 positive owners had lower CJ values. Even experimentally infected dogs showed no nasal and oral virus shedding, with transient presence in feces. Seronegative dogs from SARS-CoV-2 positive owners with lower CJ the values could also be due to an early serum collection of seven days instead of 14 days. Generally, seroconversion in dogs is late, with titers between 1:40 and 1:80 against receptor binding domain (RBD) and S antigens at 14 days post infection in experimentally infected dogs. Despite the low number of samples, the detection of SARS-CoV-2 in dogs was statistically significant. Additionally, humans infected with SARS-CoV-2 had clinical signs, such as runny nose, cough or diarrhea, and higher viral load (low CJ values).
The study results raise awareness of the risk of infection between humans and dogs, especially when they have closer interactions without protection. People infected with COVID-19, especially in multi-resident households, should take the same preventive precautions with their dogs during self-isolation. It is important to note that dogs with mild clinical signs can be infected with SARS-CoV-2.
Furthermore, the study highlighted the need for a One Health approach for a better understanding of the epidemiology, prevention and control of SARS-CoV-2 transmission among different species. Researchers should pursue multidisciplinary and comparative research to understand SARS-CoV-2 transmission and prevent future pandemics, especially the role of humans and animals in environmental sharing.