Since the emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes the coronavirus disease 2019 (COVID-19), there have been numerous reports of pets becoming infected. Both dogs and cats have been observed to exhibit symptoms of infection.
A new study by researchers at the University of Technology Sydney, the University of Sydney, the Icahn School of Medicine at Mount Sinai, New York, and the Universidad de Chile shows that infected cats have shorter shedding of SARS-CoV-2 RNA compared to their human owners. The results highlight a need for large-scale epidemiological analysis of the SARS-CoV-2 infection dynamics to develop preventive measures in both humans and their pets.
The coronavirus pandemic stemmed from a localized outbreak in Wuhan City, China, where its first cases appeared in December 2019. From there, the SARS-CoV-2 has continued to spread across the globe, infecting over 48 million people. Early in the pandemic, scientists tied cross-species transmission between humans and an unknown animal reservoir to the spread of the virus.
As the pandemic evolved, scientists have found a growing body of proof that the virus can infect companion animals or pets, as well as other animal species.
So far, there have been cases reported to the World Organization for Animal Health (OIE) and the United States Department of Agriculture. These include 14 cases among dogs in the United States (US), Japan, and Hong Kong, and 25 cases in cats in Hong Kong, the US, Germany, Belgium, Russia, Spain and the United Kingdom.
Apart from domesticated animals or pets, some cases in farmed animals and zoo animals were also reported. Cases of SARS-CoV-2 in farmed milk were reported in the Netherlands, the US, Spain and Denmark. Tigers and lions have also been infected in a New York zoo.
In some studies, dogs have been experimentally infected with SARS-CoV-2 and showed low viral loads. This could mean that they do not transmit the virus to other dogs. Among domesticated animals, it was shown that mustelids and felids are more vulnerable to coronavirus infection than canines.
In the current study, which appeared on the preprint server medRxiv*, the team conducted active surveillance in Santiago City, Chile, starting in May to determine the possibility of infection in companion animals in households where people tested positive for SARS-CoV-2.
The team described the infection in a household of two human adults and three cats using real-time reverse transcription-polymerase chain reaction (RT-PCR) tests and enzyme-linked immunosorbent assay (ELISA) tests, viral sequencing, and viral isolation.
RNA detection of SARS-CoV-2. The horizontal axis represents the sampling date. Nasal swabs (circle), fecal samples (diamond), and sputum (triangle) samples are colored per individual. Negative samples are illustrated as Ct 41 (below the dotted line). Arrows with the corresponding caption colors indicate the day of symptom onset and the date of the SARS-CoV-2 diagnosis of humans.
What the study found
To assess the infection of the humans and cats, the team conducted clinical observations for symptoms of COVID-19 and performed serological testing (which looks for the presence of antibodies in the blood).
The humans were infected first, and after several of the cats consecutively developed respiratory symptoms and tested positive. All cats excreted detectable SARS-CoV-2 RNA for a shorter duration than humans, and the viral sequences confirmed the human to cat transmission.
The study’s findings highlight that SARS-CoV-2 can be transmitted between humans and cats living in the same household. The virus can spread to animals by direct or indirect contact with contaminated surfaces or airborne particles.
The study’s findings of positive SARS-CoV-2 RNA detection in nasal samples and fecal samples in the three cats support recommendations to prevent close contact with pets when someone in the family is infected with COVID-19.
“The findings presented here show that cats seemingly have different and shorter patterns of excretion for SARS-CoV-2 RNA compared to humans. These results highlight a need for large-scale epidemiological analysis of SARS-CoV-2 infection dynamics to support the establishment of preventive measures in real-life human-animal relationships,” the team recommended.
The spread of COVID-19 into animals also shows how vast the transmission of the virus can be. To date, there are over 48 million cases of COVID-19 across the globe. Of these, 1.22 million have already died due to the infection.
The United States reports the highest number of cases, topping over 9.48 million. India and Brazil trail behind with over 8.31 million and 5.59 million cases, respectively.
Since lockdown measures were lifted in most countries, it is important to continue implementing infection control measures to prevent skyrocketing cases. Health experts still reiterate the importance of regular hand hygiene, social distancing, and universal masking.
medRxiv 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.