The first UK case of a potentially deadly strain of the mpox virus, formerly known as monkeypox, has been detected in London.

Having said this, the risk to the UK population from the Clade Ib mpox strain “remains low”, the UK Health Security Agency (UKHSA) said.

The person involved had been on holiday in Africa and travelled back to the UK on an overnight flight on October 21.

More than 24 hours later, they developed flu-like symptoms and started to develop a rash on October 24 which worsened in the following days.

Potentially deadly strain of Mpox detected in London

On October 27, the person went to an emergency department in London where they were swabbed, tested and sent home to isolate while waiting for the results.

They have now been transferred to the Royal Free Hospital high consequence infectious diseases unit for treatment.

Less than 10 people who are thought to have come into contact with the patient are initially being traced, the UKHSA said.

These are household contacts, although the UKHSA is “still working” on the number of people it may have to contact trace.

What is Mpox and what are the symptoms?

Mpox "is a rare infection most commonly found in parts of central and east Africa", the NHS explains.

Mpox spreads between people when there is close contact and the risk of catching mpox in the UK is low.

The first symptoms of mpox usually take between five and 21 days to appear.

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These include:

  • a high temperature (fever)
  • a headache
  • muscle aches
  • backache
  • swollen glands
  • shivering (chills)
  • exhaustion
  • joint pain

You can find out more about mpox via the NHS website.

As of early September, over 600 deaths from the virus had been reported.

The World Health Organisation (WHO) has declared a public health emergency of international concern because of the rapid spread of the mpox strain.

Professor Susan Hopkins, chief medical adviser at the UKHSA, said: “It is thanks to our surveillance that we have been able to detect this virus.

“This is the first time we have detected this Clade of mpox in the UK, though other cases have been confirmed abroad.

“The risk to the UK population remains low, and we are working rapidly to trace close contacts and reduce the risk of any potential spread.

“In accordance with established protocols, investigations are underway to learn how the individual acquired the infection and to assess whether there are any further associated cases.”

Health and Social Care Secretary Wes Streeting said: “I am extremely grateful to the healthcare professionals who are carrying out incredible work to support and care for the patient affected.

“The overall risk to the UK population currently remains low and the government is working alongside UKHSA and the NHS to protect the public and prevent transmission.

“This includes securing vaccines and equipping healthcare professionals with the guidance and tools they need to respond to cases safely.

“We are also working with our international partners to support affected countries to prevent further outbreaks.”

According to the UKHSA, the UK has an existing stock of mpox vaccines and last month announced further vaccines are being procured.

This strain of mpox is different from mpox Clade II that has been circulating at low levels in the UK since 2022, primarily among gay, bisexual and other men who have sex with men.

The UKHSA said that while the existing evidence suggests mpox Clade Ib causes more severe disease than Clade II, it will continue to monitor it and learn more.

It said it will initially manage Clade Ib as a high consequence infectious disease.