Covid is common in pet cats and dogs whose owners have the disease, research suggests, reports BBC.
Swabs were taken from 310 pets in 196 households where a human infection had been detected.
Six cats and seven dogs returned a positive PCR result, while 54 animals tested positive for virus antibodies.
"If you have Covid, you should avoid contact with your cat or dog, just as you would do with other people," Dr Els Broens, from Utrecht University, said.
"The main concern is not the animals' health but the potential risk that pets could act as a reservoir of the virus and reintroduce it into the human population."
The authors of the study said no evidence of pet-to-owner transmission had been recorded to date but it would be difficult to detect while the virus was still spreading easily between humans.
Most infected pets tend to be asymptomatic or display mild Covid symptoms.
Researchers from Utrecht University sent a mobile veterinary clinic to households in the Netherlands that had tested positive for Covid at some point in the past 200 days.
Swabs were taken from their pet cats and dogs to test for evidence of a current infection, while blood samples were also tested for antibodies suggesting a past exposure to Covid.
The results were presented at the European Congress of Clinical Microbiology and Infectious Diseases:
• 4.2% showed evidence of a current infection
• 17.4% tested positive for antibodies
Follow-up tests showed all the PCR-positive (polymerase chain reaction) animals cleared the infection and went on to develop antibodies.
The researchers say the most likely route of virus transmission is from human to animal, rather than the other way round.
"We can't say there is a 0% risk of owners catching Covid from their pets," Veterinary Microbiological Diagnostic Centre Dr Broens said.
"At the moment, the pandemic is still being driven by human-to-human infections, so we just wouldn't detect it."
Vets in Russia have started vaccinating some animals against the disease.
But Dr Broens said: "I don't see the scientific evidence for that now.
"It seems unlikely that pets play a role in the pandemic."
A separate study run by the University of Guelph in Ontario, Canada, found cats that slept on their owner's bed seemed to be at particular risk of infection.
A total of 48 cats and 54 dogs from 77 households were tested for Covid antibodies and their owners asked about their interaction with their pets.
About 67% of the owned cats and 43% of the owned dogs tested positive, compared with 9% of dogs and cats from an animal shelter and 3% of stray cats in the area.
A quarter of the pets displayed a symptom of the disease, from loss of appetite to difficulty breathing.
And although most cases were mild, three were severe.
The study's authors said cats' biology may make them more susceptible to Covid.
Cats are also more likely to sleep near their owner's face than dogs, increasing their exposure to any infection.
'Robustly conducted'
Cambridge University veterinary medicine department head Prof James Wood said the two studies added to other evidence suggesting a substantial proportion of cats and dogs may catch the virus from their owners.
"The Dutch study is robustly conducted and shows that around 20% of exposed pets may be infected and that they eventually clear the infection just as most humans do," he said.
"Most reports are that this infection appears to be asymptomatic.
"It also seems that the virus does not normally transmit from dogs and cats to either other animals or their owners."