Spain and Portugal have detected over 40 suspected cases of monkeypox, a rare disease, with the majority of the cases occurring in the Madrid and Lisbon areas.

The World Health Organization is working with the government to investigate the outbreak after the British health authorities said they had detected seven cases so far this month.

Some of these infections may be transmitted through sexual contact among gay or bisexual men, which would be a new development in understanding how the virus is transmitted.

In a statement, health authorities in the Madrid region said they had detected 23 possible cases of monkeypox and all of them were believed to have been transmitted through sexual activity.

In general, its transmission is via respiratory drops but the characteristics of the 23 suspected infections point to it being passed on through bodily fluids during sex relations, according to a statement.

Elena Andradas, head of public health in the Madrid region, said that most of them are men who have sexual relations with other men, but not all of them.

There are 20 suspected cases of monkeypox in the Lisbon region, according to the health ministry.

The majority of the cases were young males who had ulcerated skin.

The symptoms of monkeypox in humans include a rash on the face, a high temperature, muscle ache, and chills. The majority of people recover from the illness in a few weeks.

Close contact with animals such as rodents and monkeys is the most common method of transmission. In rare cases, it has been fatal.

The UK Health Security Agency said on Monday that it had detected four new cases after three cases in May.

The four additional cases were all men who have sex with men.

The first of the three confirmed cases was linked to travel from Nigeria, raising fears of community spread of the virus.

Agence France-Presse