Even a single lesion may also signal infection from the monkeypox virus, especially if the individual has had a new sexual partner recently, according to officials at the UK Health Security Agency (UKHSA).

After the World Health Organisation (WHO) declared the infection disease as a public health emergency of international concern, the UKHSA updated the case definition for monkeypox. This will help both individuals and clinical professionals identify monkeypox symptoms, the agency noted.

In a statement, the UKHSA said the symptom list has been expanded to include a single lesion or lesions on the genitals, anus and surrounding area, and lesions in the mouth. The new list also added anal or rectal pain and bleeding, known as proctitis, especially if the individual has had a new sexual partner recently.

The majority of people with monkeypox can safely manage their symptoms at home and there have been no deaths in the UK. Most people experience mild disease but it can cause a significant illness in some, requiring hospitalisation, including severe pain.

"We continue to see new diagnoses of monkeypox, passed on primarily through close or sexual contact," said Meera Chand, Director of Clinical and Emerging Infections at UKHSA, in the statement.

"We have updated our case definitions to reflect the clinical presentations that have been seen during this outbreak. It is important to recognise that just one or two genital or anal lesions or lesions in the mouth can be signs of monkeypox, especially if you have had a new sexual partner," she added.

In addition to these, high fever, chills, headache, exhaustion, muscle aches (myalgia), joint pain (arthralgia), backache, and swollen lymph nodes (lymphadenopathy) also signal a possible infection. There is still a need to be cautious and stay alert for symptoms, the UKHSA said. Chand advised people with monkeypox symptoms to "stay at home and contact local sexual health service for advice".