Health officials are concerned over rising cases of monkeypox in North America and Europe, as the disease is usually endemic in parts of Africa.

More than 40 verified cases of monkeypox were detected in Spain and Portugal, with Canada being the latest country to say that it is investigating dozens of suspected cases.

Most people recover from the virus in several weeks, and fatalities are rare. Thousands of people were infected in Central and Western Africa in recent years, but cases are rare in Europe and North America. The WHO said it was investigating that many of the reported cases involved gay or bisexual individuals.

Monkeypox has not previously been characterized as a sexually transmitted disease, a US Central for Disease Control and Prevention statement said on Wednesday that "anyone, regardless of sexual orientation, can spread monkeypox through contact with body fluids, monkeypox sores, or shared items (such as clothing and bedding) that have been contaminated with fluids or sores of a person with monkeypox." The statement further added that household disinfectants can kill the virus on surfaces.

Since May 6, Britain has confirmed nine cases, and the US verified its first case on Wednesday in Massachusetts. The man tested positive for the virus after he visited Canada.

"We really need to better understand the extent of monkeypox in endemic countries... to really understand how much is circulating and the risk that it poses for people who are living there, as well as the risk of exportation," infectious disease epidemiologist Dr. Maria Van Kerkhove said at a WHO press conference on Tuesday on global health issues.

Monkeypox is a rare viral disease transmitted to humans from animals, with 1% to 10% lethality. Among people, the disease is not spread easily, but it may have complications. It predominantly occurs in Central and West Africa and causes swelling of the lymph nodes and a widespread rash on the body.