What are the two different strains of monkeypox? Types of disease explained - and which is circulating in UK

Monkeypox cases are continuing to rise in the UK, with more than 470 cases now identified.

But what are the two different strains of monkeypox and which one has been found in the UK?

Here’s what you need to know.

What are the two different strains of monkeypox?

According to the World Health Organization (WHO), there are two distinct genetic clades (types) of the monkeypox virus. These are the central African (Congo Basin) clade and the west African clade.

The WHO said: “The Congo Basin clade has historically caused more severe disease and was thought to be more transmissible.

“The geographical division between the two clades has so far been in Cameroon, the only country where both virus clades have been found.”

Dr Mike Skinner, reader in virology at Imperial College London, said the genomic sequences of the two strains were first obtained and compared in 2005, which gave clues as to why the West African strain is milder.

He said the central African (Congo) strain has mortality in Africa of up to 10%, but the West African strain is milder, with mortality in Africa of 1 to 2%.

Martin Michaelis, professor of molecular medicine at the University of Kent, added: “As far as we know, the current British cases have been caused by monkeypox viruses from the less deadly West African clade.”

However, Prof Michaelis said the mortality rates were determined in African countries with limited health care capacities so we will therefore “have to learn how deadly monkeypox is in a high income country like the UK with an advanced health care system and intensive care facility”.

How did the outbreak start and how has it spread?

Dr Skinner said the UK has had “sporadic, international, travel-related cases” of monkeypox since an apparent increase in numbers in West Africa in 2017.

He said the first cases identified earlier this year seem to be similar, but the latest cases identified in May - both here and abroad - are in clusters and predominantly with no travel history to West Africa.

Dr Skinner added: “They seem to be linked in having extensive, close and intimate network contacts - in this case by being members of the men who have sex with men community.

“Public health officials are looking for links between the clusters, nationally and internationally, as well as for earlier and hopefully index cases - although it is assumed their origin is West Africa, they may represent multiple introductions.”