London School of Hygiene & Tropical Medicine

A single case of Clade Ib mpox has been detected in the UK, the UK Health Security Agency (UKHSA) has confirmed.

Mpox is an infectious disease with similar but less severe symptoms to smallpox. There are broadly two clades or families of the mpox virus, referred to as Clade I and Clade II. Clade II predominantly circulates in West Africa and caused the large outbreak in 2022. In Central Africa, Clade Ia and Ib are currently circulating.

Both clades cause broadly similar illnesses including generalised fever, muscle aches and headaches. A distinctive symptom includes a rash with blisters or ulcers, which can start at the point where you came into contact with the virus but can then spread around the body. In general, Clade I appears to be more severe than Clade II.

A large outbreak of the Clade Ib mpox virus is currently impacting communities in the Democratic Republic of the Congo (DRC). The outbreak has resulted in smaller outbreaks in other countries in the region, including Kenya and Rwanda, and several cases have been detected outside of Africa in countries such as Sweden, Germany, India and now the UK.

According to the UKHSA’s statement, the person currently being treated in the UK had recently travelled to affected countries. It is important to note that while there have been cases outside Africa they have not led to widespread outbreaks within those countries.

Experts urge continued support for the countries most affected by mpox outbreaks, with the release of adequate funding or vaccination to support the experienced teams within DRC who can manage the outbreak there with the right support from the global community.

Michael Marks, Professor of Medicine at the London School of Hygiene & Tropical Medicine (LSHTM) and Honorary Consultant in Infectious Diseases at the Hospital for Tropical Diseases, University College London Hospital, said:

“The mpox virus itself isn’t that transmissible as it relies predominantly on direct skin-to-skin contact with a person who is currently unwell with mpox. By contrast, the COVID-19 virus transmits through the air and a lot of transmission occurs from individuals who have mild symptoms or are asymptomatic, which is why it can spread so widely. By comparison the mpox virus is much less transmissible.

“Wherever there are a large number of cases occurring in a part of the world people are traveling to and from, there is always some risk of a small number of mpox cases being introduced into other countries. We need to make a distinction between the risk of one or two cases being imported into other parts of the world, as we’re currently seeing, versus this leading to onwards transmission and widespread outbreaks in that country.

“Sweden has not had further cases arising from its imported case and in the UK, the risk that there will be lots of other cases arising from this imported case is again low. So, although there is, and I anticipate will continue to be, a large number of cases occurring in Africa, the likelihood overall that there will be an epidemic on the scale of the COVID-19 pandemic is extremely low.

“Although the clade I mpox viruses appear to cause slightly more serious illness, overall, outcomes for most people are good and patients typically have a mild or self-limiting illness from which they will fully recover. The healthcare system in the UK is ready to respond to mpox cases and has excellent access to infectious diseases teams, specialist care and vaccines.

“The priority must continue to be on supporting the countries most affected with the release of adequate funding or vaccination to control this mpox outbreak. The teams in DRC are very experienced, and with the right resources, they can handle it. But what’s required is vaccine access.”