LONDON, May 19 (Reuters) - A handful of cases of monkeypox have now been reported or are suspected in Britain, Portugal, Spain and the United States.

The UK cases have been reported as the West African strain.

The United States has also reported one case.

Transmission this time is puzzling experts, because a number of the cases in the United Kingdom - nine as of May 18 - have no known connection with each other.

"My working theory would be that there's a lot of it about in west and central Africa, travel has resumed, and that's why we are seeing more cases," said Whitworth.

But it also protects against monkeypox, and so the winding down of vaccination campaigns has led to a jump in monkeypox cases in areas where the disease is endemic, according to Anne Rimoin, an epidemiology professor at UCLA in California.