The United States (U.S.) Centres for Disease Control and Prevention raised its monkeypox alert level on Monday and recommended travellers wear masks.
Although he cautioned that monkeypox was not on the same level of concern as COVID-19.
Monkeypox presented as flu-like symptoms before patients develop a painful rash and lesions and swollen lymph nodes.
The incubation period between exposure and when symptoms first appear can be anywhere from five to 21 days, according to the World Health Organisation.
The CDC said cases have been reported on every continent aside from Antarctica.
“Some cases were reported among men who have sex with men.
“Some cases were also reported in people who live in the same household as an infected person,” the CDC said.
Experts said a number of sexually transmitted infections present similar symptoms and the real number of infections could be higher.
The agency reported 31 confirmed cases in the U.S. as of Monday afternoon.
The first reported cases in Washington, D.C., came on Sunday.