The Lancet records that, 12 days after their symptoms began, their four-year-old male Italian greyhound developed lesions and later tested positive for monkeypox via PCR testing.
DNA comparison between the virus found in the dog and in the owners showed a link.
The men reported co-sleeping with their dog but said they had kept their dog isolated after they began to show symptoms, nearly two weeks before the dog's lesions appeared.
In the African nations where monkeypox has been endemic for years the virus is found in rodents and primates.
The virus has also been found in captive primates that came into contact with infected animals and in prairie dogs in the US.
Researchers said evidence in this case led them to believe there has been human-to-animal transmission and added that their findings should "prompt debate on the need to isolate pets from monkeypox virus-positive individuals".
Monkeypox in NZ
A fourth case of monkeypox was detected in New Zealand, in a person who had recently returned to the South Island from overseas.
As with the previous three cases of monkeypox in New Zealand, the Ministry of Health said they regarded the risk of community transmission as low.
A third case of monkeypox was confirmed earlier this month after a person returned from international travel.
That person was also isolating in the South Island.
Two previous cases had been reported in New Zealand in July. By the end of the month, health officials reported they had since recovered.
Ministry public health advice for those with monkeypox is to isolate at home until the scabs from lesions have fallen off.
Monkeypox virus is part of the same family of viruses as variola virus, which causes smallpox.
