Health authorities are on alert for the spread of monkeypox, a rare viral disease first reported in the Democratic Republic of Congo in the 1970s, after new cases emerged in Europe, and the United States confirmed its first infection.

Portugal said on Wednesday it had identified five cases of monkeypox, Spain said it was testing 23 potential cases, and the US state of Massachusetts announced it had found a case in a man who recently travelled to Canada.

The United Kingdom was the first to confirm a case of monkeypox earlier this month. It has now detected seven cases and is working with the World Health Organization (WHO) to investigate the virus’s spread after being unable to make a link between the initial case, in a man who had travelled from Nigeria, and the more recent ones.

Health authorities suspect some of the infections may have occurred through sexual contact – in this instance among gay or bisexual men – with four of the UK cases identified among people who visited sexual health clinics after developing the rash associated with monkeypox.

“No source of infection has yet been confirmed for either the family or GBMSM clusters,” the WHO said in a statement in Wednesday. “Based on currently available information, infection seems to have been locally acquired in the United Kingdom. The extent of local transmission is unclear at this stage and there is the possibility of identification of further cases.”

Monkeypox, which is similar to human smallpox, typically begins with a flu-like illness and swelling of the lymph nodes, followed by a rash on the face and body. Most people recover from the illness, which is endemic in parts of central and western Africa and usually the result of close contact with infected animals, within a few weeks, but it can be fatal.

The five Portuguese patients, out of 20 suspected cases, are all in a stable condition, according to the country’s health authorities. They are all men who live in the region of Lisbon and the Tagus Valley, they added.

Health authorities in Madrid said the cases discovered in Spain appeared to be linked to sexual contact.

“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,” they said in a statement, without giving further details.

“All of them are young adult males and most of them are men who have sexual relations with other men, but not all of them,” Elena Andradas, head of public health in the Madrid region, told Cadena Ser radio.

US health officials said the Massachusetts man who developed monkeypox went to Canada to see friends at the end of April and returned home in early May. He is currently being treated in hospital.

Jennifer McQuiston from the US Centers for Disease Control and Prevention (CDC) said while it was the only case the CDC was aware of, “I do think we are preparing for the possibility of more cases”.

The agency is in contact with its counterparts in the UK and Canada as part of the investigation, but McQuiston said no link had been established so far.

There are two types of monkeypox virus: the West African clade and Congo Basin (Central African) clade. The case-fatality ratio for the West African clade has been documented to be about 1 percent, and up to 10 percent for patients with the Congo Basin clade.

The WHO said that while smallpox vaccination has been effective against monkeypox, the end of mass vaccination programmes for smallpox meant people under the age of 40 or 50 no longer had that protection.

The UK has previously reported cases of monkeypox – all linked to travel to Nigeria – as has the US. An outbreak there in 2003 was traced to pet prairie dogs that had been housed with small animals imported from Ghana that were found to have the virus. (Courtesy Al Jazeera)

•Photo: Monkeypox is endemic in west and central Africa with cases outside those areas linked to travel. However, cases reported in the UK, Spain and Portugal appear to have spread through sexual contact

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