The World Health Organisation warned people with the virus to keep away from their pets after the case in France, reported in The Lancet.
A Paris gay couple who had been infected with the virus reported lesions on their Italian greyhound dog 12 days after their own symptoms began.
The dog had been sleeping in the same bed as its owners and genetic tests showed it was the same strain of the virus carried by their owner, the French researchers concluded.
“Whether domesticated cats and dogs could be a vector for monkeypox virus is unknown,” the researchers said, meaning it is not known whether they can pass it on to humans or other animals.
Monkeypox infection among domesticated animals, such as dogs and cats, has never been reported before, though previous cases have been reported in primates, squirrels and chinchillas in the wild.
The researchers added: “Our findings should prompt debate on the need to isolate pets from monkeypox virus-positive individuals. We call for further investigation on secondary transmissions via pets.”
Dr Rosamund Lewis, technical lead on the monkeypox response at the WHO, said: “We believe it is the first instance of a canine being infected, however, this has been a theoretical risk – you may see that a number of public health agencies have advised those who contract monkeypox to make every effort to isolate from their pets because of this hypothetical risk.”
She added that it was also important to consider “contamination of animals outside the household, for example, for those accessing garbage and things like that.”
Case numbers and how monkeypox spreads
There have been more than 34,448 confirmed cases of Monkeypox in 82 countries so far in 2022, with 3,017 in the UK alone.
The virus can be spread through close contact, and cases in Europe and the US are overwhelmingly spreading among gay, bisexual and queer men (men who have sex with men), with the infection being passed on mainly through close contact in interconnected sexual networks.
The virus can be extremely painful and serious, with around one in 10 cases requiring hospital care, though only a few deaths have been attributed to the outbreak.
Dr Mike Ryan, director of the WHO’s Health Emergencies programme, said: “In this particular case, transmission to a dog in a closed domestic setting, (with) one animal infected, is not unusual, it’s not unexpected.
“But what we don’t want to see happen is disease moving from one species to the next, and then remaining in that species (and) moving around within a new species because that’s when the virus can adapt, and then adapting to that new species (the virus) is incentivized to evolve as such.”
Dr Sylvie Briand, director of global infectious hazard preparedness at the WHO, added: “It’s the first time, so it means that dogs can be infected, but it doesn’t mean that the dog can transmit the disease and infect other dogs, nor does it mean that the dog can re-infect human if it is infected.”
Dr Tedros Adhanom Ghebreyesus, the WHO’s director general, also told the press briefing: “More than 35,000 cases of Monkeypox have now been reported to WHO, from 92 countries and territories, with 12 deaths.
“Almost 7,500 cases were reported last week, a 20 per cent increase over the previous week, which was also 20 per cent more than the week before.
“Almost all cases are being reported from Europe and the Americas among men who have sex with men, underscoring the importance for all countries to design and deliver services and information tailored to these communities that protect health, human rights and dignity.
“However, for the moment, supplies of vaccines, and data about their effectiveness, are limited, although we are starting to receive data from some countries.”