The recent outbreak of monkeypox is unusual but is still containable, according to the World Health Organization.

"It's not something we've seen over the last few years," said Sylvie Briand, director of the WHO's epidemic and pandemic preparedness and prevention department Tuesday. She said it's still containable and that countries can cut the chain of transmission by raising awareness and getting people to recognize the symptoms early.

The illness itself begins like many acute viral diseases — with high fever, muscle pain and swollen lymph nodes. Those symptoms can be followed by a skin rash often starting in the face before spreading elsewhere and sometimes growing into fluid-containing pustules that form a scab. The illness usually lasts two to four weeks.

Monkeypox, which has been afflicting developing countries for years, has spread across Europe and the U.S. in recent days, leading to a total of 131 confirmed cases to date and 106 suspected cases under investigation across 19 nations, according to Briand.

The virus belongs to the Orthopoxvirus genus, which includes the variola virus, the cause of smallpox; the vaccinia virus, which is used in the smallpox vaccine; and cowpox virus. Monkeypox is less contagious than smallpox and the symptoms are milder. A large proportion of cases have been among men who have sex with men, and many have occurred within sexual networks, though anyone can contract the disease regardless of sexual orientation.

The unusual spread means the WHO is looking into whether the virus mutated or whether a change in human behavior and contact after the pandemic has contributed to the spread. Initial studies indicate the virus hasn't mutated, Briand said. The WHO is waiting for more data on the subject.

While a number of medical countermeasures exist, such as treatments and vaccines, some of the new shots are in limited quantity and some are not fully licensed to be put on the market, Briand said.

The Centers for Disease Control and Prevention has told gay and bisexual men that monkeypox appears to be spreading in the community globally, CNBC reported, citing official John Brooks.

"There's one pandemic we're still in the middle of, and another emerging zoonosis that once again breached the species barrier is now transmitting in multiple countries," said Mike Ryan, head of the WHO's health emergencies program. "It's a containable event nonetheless."

The spread hasn't been confined to men. Some women have gotten infected, and the disease can be spread through vaginal fluids.