SEVERE monkeypox patients may be infectious for up to ten weeks, scientists fear.
An investigation of previous patients who had the disease found one man tested positive more than 70 days after he first showed symptoms.
It comes as cases of the virus reach 71 in the UK, and health officials have urged people to stay alert to symptoms.
Signs of the disease in the early stages include fever, headache, chills, back and muscle aches.
A rash may develop between one and five days later, which at first looks like chickenpox before turning into blisters that scab over.
People can catch the virus from others by touching their scabs or lesions, having close physical contact, touching contaminated objects or being exposed to respiratory droplets.
Patients are contagious until their scabs fall off, the UK Health and Security Agency (UKHSA) says, and the scabs themselves can contain viral material.
However, the latest study, published in The Lancet Infectious Diseases, suggests people may be infectious long after their rash has settled.
Researchers looked at seven cases of monkeypox in the UK between 2018 and 2021.
One of the patients, an unnamed man in his 40s, caught monkeypox in Nigeria before being hospitalised in the UK.
He was in hospital for 39 days before doctors said he had recovered, and he was sent home.
But six weeks later, when he had sex for the first time since his bout of illness, the tell-tale monkeypox rash returned.
The man also had swollen lymph nodes, which are a sign of infection.
At hospital, a test that swabs the throat revealed the man was positive for monkeypox.
The findings suggest that the man was infectious, given that he had the rash again.
Study author Dr Hugh Adler, from the Liverpool School of Tropical Medicine, said: “It remains positive in the throat and blood for the length of the illness and maybe even longer after the rash is resolved.
“We don’t know that this means these patients are more infectious or infectious for longer, but it does inform us of the biology of disease.”
It is not clear if the man would have been contagious in the six-week period between hospital discharge, and his “relapse” after having sex.
Dr Adler said researchers were “surprised” that monkeypox could be detected in the throat and blood for that length of time, MailOnline reported.
A relapse such as this has not been reported before, the paper authors wrote.
But they noted they were “unaware of any reports of monkeypox virus detection in seminal fluid”.
Other people in the study were positive on respiratory PCR tests for between seven and 17 days.
All made a full recovery and none suffered severe complications.
The World Health Organization says symptoms of monkeypox usually start from six to 13 days after infection, but can range from five to 40 days.
A person is not contagious during this so-called incubation period.
They are able to spread the virus once they are showing symptoms, including the rash.
Health officials have so far said that patients with monkeypox in the current outbreak have typically had a mild illness.