MONKEYPOX patients could be infectious for up to four weeks, experts say, as the virus is recorded in 11 countries.
Dr Amesh Adalja, an infectious disease experts at John Hopkins University, issued the stark warning as Europe grapples with an monkeypox outbreak.
People who catch the virus will first suffer from a fever before rashes and skin lesions break out on the face and body.
It's when skin lesions appear that the disease becomes highly infectious.
"It can take a few weeks for the skin lesions to disappear," he told .
"People are contagious until their active skin lesions have dissipated."
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Dr Michael Head, a global health expert at Southhampton University in England, backed up Dr Amesh's assertion.
"Based on previous monkeypox outbreaks and guidance from [UK health authorities] and WHO, the infectious period (i.e. when the virus can be transmitted to another person) can be comparable to the time period where the rash and blisters are present," he said.
"This may be for two weeks, and may be longer.
"Specifically here in this outbreak, we’re learning more about the cases and their presentations, and so many basic questions about their epidemiology are still to be clarified.
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"However, if onward transmission can indeed take place over a longer period of time, early identification of any possible cases is going to be vital in efforts to break those chains of transmission and contain the outbreak."
It comes as cases of monkeypox doubled in the UK in just a week - as a further 11 infections have been detected.
The US, Canada and Spain are among 11 countries to register confirmed cases.
To combat the 'unprecedented' outbreak, ministers have stockpiled doses of the vaccine, as cases hit 20.
Monkeypox is a rare disease with most cases being found in Africa.
But there are currently outbreaks in Britain, Portugal, and parts of Europe.
Medics have urged people to be on the look out for signs, which can include fever, headaches, swellings, aches, chills and exhaustion.
A rash can develop, often beginning on the face, which then spreads to other parts of the body including the genitals.
It spreads between humans only through close contact.
According to the World Health Organisation (), monkeypox virus is similar to human smallpox and while it is much milder, it can be fatal.
Professor Kevin Fenton London’s Public Health Director said: "At this point, we’re asking everybody to be aware of the signs and symptoms which include rashes around the mouth, as well as around the genital area."
Health Secretary Sajid Javid today announced he had updated the G7 on the situation in the UK.
In a tweet this afternoon, he said the UK Health Security Agency (UKHSA) had identified a further 11 cases - brining the total to 20.
He added: "Most cases are mild, and I can confirm we have procured further doses of vaccines that are effective against monkeypox."
Globally, 127 cases have been reported in 11 countries, according to John Brownstein, professor of medicine at the Harvard Medical School in the US, who is keeping track of cases.
Professor of International Public Health at the London School of Hygiene and Tropical Medicine Jimmy Whitworth said cases need to be identified, isolated and treated.
He said that there is a 'need to engage with the at-risk community of gay and bisexual men to ensure they know about the presence of this infection and report any sign and symptoms to health facilities'.
What are the 7 signs of monkeypox you need to know
People infected with monkeypox will usually start to experience symptoms five to 21 days after initial infection.
The NHS says the first symptoms are:
- a high temperature
- a headache
- muscle aches
- backache
- swollen glands
- shivering (chills)
- exhaustion
They added that a rash usually appears one to five days after the symptoms.
While monkeypox is not considered to be a sexually transmitted infection, it can be passed on between direct contact from sex.
At present, health chiefs are urging men who are gay and bisexual to be aware of any unusual rashes or lesions.
It's believed the Government has accepted more cases will be found over the coming days.
Earlier this week it was revealed that the latest infected Brits live in London and the South East.
It's thought two new infections, which were detected yesterday, were picked up in the UK.
Neither of the patients had travel links to countries where the virus is at an endemic stage.
Dr Susan Hopkins, Chief Medical Adviser at the UK Health Security Agency (UKHSA) said that the spread in countries across Europe confirms concerns that there could be a spread in communities.
While experts have said the overall risk remains low, Javid has ordered the UKHSA to take a belt and braces approach and secure a further 20,000 doses.
The Health Secretary had previously secured 5,000 vials of the monkeypox jab last year to ensure Britain was prepared.
A Whitehall source said: "Sajid directed procurement of the relevant vaccine months ago as a precautionary measure but we are making sure we are further ahead of the curve by taking decisive action to secure even more of the vaccine.
"We aren’t too worried at this point but will be keeping a very close eye on the situation. It’s better to be safe than sorry."
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The illness is usually mild and most people recover in two to four weeks.
The NHS says you will usually need to stay in a specialised hospital so the infection doesn't spread and your symptoms can be treated.
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