Mpox, also known as monkeypox, was first identified by scientists in 1958 when there were outbreaks of a "pox-like" disease in monkeys.
The dog tested positive for monkeypox 12 days after sleeping in the same bed as the owners who were infected with the virus.
The Fresno County Department of Public Health is planning a larger monkeypox vaccine clinic in the next week.
The outbreak has mostly affected men who identify as gay, bisexual or other men who have sex with men, although the CDC has warned it is not a sexually transmitted disease and anyone is at risk of infection.
As monkeypox cases continue to increase, an expert is weighing in on how the virus is spread.
So far, just 430 doses of the monkeypox vaccine have been allocated to Fresno County, but health officials say they've already asked for more.