EXPLAINER | Why monkeypox cases are rising in Europe

An outbreak of monkeypox in the United Kingdom, Portugal and Spain is a cause of concern as the disease, which mostly occurs in west and central Africa, has very occasionally spread elsewhere. Here's what we know

A handful of cases of monkeypox have now been reported or are suspected in the United Kingdom, Portugal and Spain.

The outbreaks are raising alarm because the disease mostly occurs in west and central Africa, and only very occasionally spreads elsewhere.

Here's what scientists know so far.

Monkeypox is a virus that causes fever symptoms as well as a distinctive bumpy rash. It is usually mild, although there are two main strains: the Congo strain, which is more severe with up to 10% mortality and the West African strain, which has a fatality rate of more like 1% of cases. The UK cases have been reported as the West African strain.

"Historically, there have been very few cases exported. It has only happened eight times in the past before this year," said Jimmy Whitworth, a professor of international public health at the London School of Hygiene and Tropical Medicine, who said it was "highly unusual".

Portugal has logged five confirmed cases, and Spain is testing 23 potential cases. Neither country has reported cases before.

The virus spreads through close contact, both in spillovers from animal hosts and, less commonly, between humans. It was first found in monkeys in 1958, hence the name, although rodents are now seen as the main source of transmission.