The current monkeypox outbreak is just the "tip of the iceberg", the World Health Organization has said, as cases continue to be reported across the UK and Europe.
Officials confirmed 14 more cases of monkeypox in England on Tuesday, bringing the total to 70.
Health officials - including in the UK - have said that while the outbreak is “significant and concerning”, the risk to the wider population remains low.
In the past month, four times as many countries outside of Africa have reported positive cases than in the previous 50 years combined.
So far the UK, Spain, Portugal, Austria, Belgium, Denmark, France, Germany, Italy, the Netherlands, Sweden and Switzerland are among those with recorded cases.
Richard Pebody, the leader of the high-threat pathogen team at WHO Europe, said most of the confirmed cases have not been linked to travel to Africa, suggesting community transmission is taking place.
This in turn suggests there may be large numbers of undetected cases.
It is believed the illness is being spread through unsafe sex as well as other forms of transmission.
Watch: Monkeypox spreads through 'close physical contact', says WHO health official
"So we're only seeing ... the tip of the iceberg," Pebody told Reuters news agency.
Given the pace of the outbreak and lack of clarity around what is driving it, there has been concern that large events and parties this summer could make things much worse.
"I'm not saying to people don't have a good time, don't go to attend these events," Pebody added.
"It's rather around what people do at the parties that matters. So it's about safe sexual behaviour, good hygiene, regular hand washing - all these sorts of things will help to limit the transmission of this virus."
The UK government has stocks of the smallpox vaccine, which is used against Monkeypox and is being offered to very close contacts of those affected.
Those at the highest risk of contracting the disease are being asked to self-isolate at home for 21 days, with others warned to be on the lookout for symptoms.
This week, the World Health Organization said it does not believe that the monkeypox virus has mutated.
A senior executive at the UN agency said on Monday that the infectious disease that has been endemic in west and central Africa has tended not to change.
Over 100 suspected and confirmed cases in a recent outbreak in Europe and North America have not been severe, according to Maria van Kerkhove, the WHO's emerging diseases and zoonoses lead and technical lead on COVID-19.
"This is a containable situation, particularly in Europe", she said. "But we can't take our eye off the ball with what's happening in Africa, in countries where it's endemic."
On Tuesday, the WHO stated that the number of confirmed cases reported outside the countries where it usually spreads had risen to 131 since 7 May.
“The important thing right now is to realise that this outbreak can be contained due to contact tracing and isolation,” said the head of the smallpox secretariat, which is part of the WHO emergencies programme, Rosamund Lewis.
“The cases we are seeing now are primarily in men, not exclusively, but primarily in men, who have self-described as gay, bi-sexual or men who have sex with men," Lewis said.
"We don’t know yet if this is a sexually transmitted infection. What we have described, as described earlier, the skin to skin contact is the primary mode, so it’s entirely possible to contract an infection through skin to skin contact, through very close contact and we have no, we don’t yet have the information as to whether this would be transmitted through body fluids for example.”
Monkeypox is a usually mild viral infection that is endemic in parts of west and central Africa. It spreads chiefly through close contact, and until the recent outbreak has only rarely been seen in other parts of the world. The majority of the recent cases have been reported in Europe.
Symptoms include a fever and a distinctive bumpy rash. The West African strain of monkeypox, which is the one identified in the current outbreak, has a mortality rate of around 1%.