Men are involved in all the Portuguese cases, most of them young, authorities said. They have skin lesions and are known to be stable. Authorities did not say whether there was any connection between the men’s travel history in Africa or recent events in Britain or elsewhere.
British health authorities said earlier this week that they had identified four cases of monkeypox spreading among gay and bisexual men in London. Spain’s health ministry says it has identified eight suspected cases of monkeypox that need to be confirmed.
The disease belongs to a family of viruses that include chickenpox and smallpox. Most people recover from monkeypox in a matter of weeks.
Dr Ibrahim Sauce Fall, assistant director general of the World Health Organization for Emergency Response, said the spread of monkeypox in the UK needed to be investigated to understand how the disease was being transmitted to men who had sex with other men.
Fall said health officials still need to better understand how the monkeypox spread in general, even in countries where it is endemic.
He noted that while more than 6,000 cases were reported in the Congo and about 3,000 in Nigeria last year, there was still “much to be known about the dynamics of transmission”.
Britain has previously reported three previous cases of monkeypox, two belonging to the same family and a third traveling to Nigeria, where the disease is most common in animals.
The virus is usually transmitted from infected animals, such as rats, to humans, although human-to-human transmission has been reported. In humans, the disease is spread through very close contact with contaminants such as wounds, body fluids, shortness of breath, or bed sheets.
Some British experts say the soon-to-be-concluded monkeypox spread through sexual contact, although outbreaks there suggest that possibility.
“Recent events indicate a potentially innovative way to spread the virus,” said Neil Mabot, a pathologist at the University of Edinburgh.
Keith Neal, an infectious disease specialist at the University of Nottingham, said the infection could not be spread through sexual activity but only through “close contact related to sexual intercourse”.
Monkeypox usually causes fever, runny nose, rash and sores on the mouth or genitals due to smallpox. A vaccine invented against smallpox has been approved for monkeypox, and several anti-virals also appear to be effective.
Contributed by Cheng from London. Joe Wilson contributed from Barcelona, Spain.