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expert reaction to UK cases of monkeypox

The UK Health Security Agency (UKHSA) has detected a number of monkeypox cases in England.


Comments on the suggestion that the cases acquired the infection via sexual contact as a novel route of transmission:

Professor Kate Baker, Chair in Applied Microbial Genomics, University of Liverpool, said:

“The transmission is likely occurring as a result of the close skin to skin contact that occurs during sex rather than being a truly sexually transmitted infection. This is similar to the sexually transmissible nature of some diarrhoeal pathogens (like Shigella) that are normally faeco-orally transmitted, among men who have sex with men (MSM).”


Dr Michael Skinner, Reader in Virology, Imperial College London, said:

“Although the current cluster of cases is in men who have sex with men, it is probably too early to make conclusions about the mode of transmission or assume that sexual activity was necessary for transmission, unless we have clear epidemiological data and analysis. Typically, we would exclude other causes before jumping to the conclusion that sexual transmission of an infection has occurred.

“Although this is the first time we have seen monkeypox in this group, that may just be because previously the numbers of cases have been low and so specific groups are less likely to have been captured in the statistics.

“By nature, sexual activity involves intimate contact, which one would expect to increase the likelihood of transmission, whatever a person’s sexual orientation and irrespective of the mode of transmission.”


Prof Francois Balloux, Professor of Computational Systems Biology and Director of UCL Genetics Institute, University College London (UCL), said:

“I would urge some caution at this stage before concluding that monkeypox has morphed into a Sexually Transmitted Infection (STI). Monkeypox is not particularly transmissible and the number of cases to date where the route of transmission is known remains relatively small.

“What is known is that monkeypox is transmitted between people in close contact through body fluids, respiratory droplets, lesions or even contaminated materials such as bedding. ‘Sexual contact’ very generally qualifies as ‘close contact’.

“Thus, the recent observations of apparent transmission through sexual contact in the UK do not necessarily imply any recent change in the virus’ route of transmission.”


Prof Keith Neal, Emeritus Professor in the Epidemiology of Infectious Diseases, University of Nottingham, said:

“It may not be actual transmitted by sexual intercourse rather than the close contact associated with sexual intercourse.

“Further work looking at whether the virus is found in semen is required to say truly sexually transmitted.” 


Dr Michael Head, Senior Research Fellow in Global Health, University of Southampton, said:

“We know the monkeypox virus can be transmitted via close contact. There is no evidence that it is a sexually-transmitted virus, such as HIV. It’s more that here the close contact during sexual or intimate activity, including prolonged skin-to-skin contact. may be the key factor during transmission.

“We do see similar with other infections, for example scabies. That is a skin infection transmitted by mites. The clinical presentation is often in the groin, and the disease itself can be transmitted via the close contact of sexual or intimate activity.

“This may indeed be the first time transmission of monkeypox via sexual contact has been documented, although it has not been confirmed to be the case.

“The implications are not so significant, in that we know close contact is required for transmission, and therefore some form of close contact will have happened here. However, the social dynamics around transmission of infectious diseases means this may be useful consideration for the public health teams involved in the contact tracing process.”


Prof Jimmy Whitworth, Professor of International Public Health, London School of Hygiene & Tropical Medicine (LSHTM), said:

“The most likely mode of spread in this cluster is through close contact: touching skin or bedding, or shared utensils. There is no need to postulate actual sexual transmission through genital or oral secretions. This type of transmission between sexual partners is well documented for other infections such as shigella, giardia and pubic lice.”


Prof Neil Mabbott, Personal Chair in Immunopathology, The Roslin Institute&  Royal (Dick) School of Veterinary Sciences, University of Edinburgh, said:

“Transmission of monkeypox virus infection in humans by sexual contact has not previously been documented, and the recent cases suggest a potentially novel means of spread.  However, transmission of pox viruses via sexual contact is not unprecedented.  The pox virus responsible for the usually benign disease molluscum contagiosum can spread between people during sexual contact1.  Very close contact with an infected individual is required for the spread of the monkeypox virus.  Thus it is plausible that sexual contact with the virus from an infected individual may enable infection to occur through broken skin, mucous membranes, respiratory droplets, infected body fluids or even contact with contaminated linen.” 



Prof Paul Hunter, Professor in Medicine, The Norwich School of Medicine, University of East Anglia, said:

“Transmission of Monkeypox from one person to another can occur by skin contact with the pocks of an infected individual and this is an important pathway, often though unnoticed breaks in the skin. So, it would not be surprising that sex which does tend to require close person to person skin contact over a quite wide area of the body would also enable transmission of Monkeypox. Whether or not that is genital to genital contact or through other contact is not clear to me, though if pocks occur in the genital area than such sexual transmission is likely. “ 


Wider comments:

Dr Michael Skinner, Reader in Virology, Imperial College London, said:

“The name ‘Monkeypox’ is a misnomer. It’s primarily a disease (mostly sub-clinical) of small African animals including rodents (there are two different strains, in the Congo Basin & West Africa). Like humans, monkeys sometimes acquire infection from the small animals. It’s a poxvirus, in the same family as variola virus, which caused smallpox before it was eradicated globally in 1980. Vaccinia virus, used as the vaccine to eradicate smallpox, is also in the same family and vaccination against smallpox also protects against monkeypox.

“Virologists recognise two strains of monkeypox virus. The Congo strain is more severe (up to 10% mortality) and probably more transmissible in humans than the West African strain, the source of these latest cases, for which mortality is estimated at about 1%. Most UK cases of monkeypox are likely to be the West African strain due to the UK receiving more travelers from this region than the Congo. 

“Monkeypox seems to require close contact to spread, we’ve seen infection of close family or household members and carers in hospitals, which might also include intimate contact

“Depending on the stage of infection, close range respiratory or droplet transmission can probably occur. Direct contact with lesions will probably transmit the virus, which might enter by the mouth. When the lesions have healed, the scabs (which might carry infectious virus) can be shed as dust, which could be inhaled.

“Sporadic cases in the UK are likely to be imported occasionally by travel. It important that potential cases are identified, isolated and their contacts traced. Transmission does rely on close contact so the wider population is not at any significant risk. The UK and other countries have seen small numbers of sporadic travel-related cases in recent years. It will be important to identify the primary case of the latest cluster, whom one would assume has a relevant travel history.

“The general public have no need for concern, but clinicians and public health authorities need to be on alert to spot infected cases early to limit transmission.

“Two factors probably contribute to the cases we have seen over recent years. One is that the cessation of smallpox vaccination after the global eradication of variola virus in 1980 means that levels of cross-reactive immunity to monkeypox have now waned or disappeared, so that people can now be infected with monkeypox virus.

“The second is the possibility that the distribution of the virus in West African wildlife has altered in some way, possibly increasing or broadening, so that humans are more likely to be infected. Investigating this possibility would require extensive testing of wildlife in the field (something that field virologists in China have sadly been criticised for by some quarters).”


Prof Paul Hunter, Professor in Medicine, The Norwich School of Medicine, University of East Anglia, said:

“I have one paper that includes Monkeypox when we were looking at impact of fake news but not worked on the disease itself1.

“Monkey pox is a pox virus of the same family as Smallpox and it causes an illness that can look similar to smallpox when the rash develops, though it is less transmissible. Globally most cases are associated with Africa. The mortality rate is somewhere between 1 and 10% depending on the strain (the UK cases have a milder strain). It is thought that most infections are acquired from infected animals either pets or food animals. Most evidence is that the virus tends to be associated with rodents and in Zaire squirrels.

“There was a sizable outbreak of Monkeypox in 2003 in the US that was associated with contact with Prairie dogs that had themselves been in contact with small mammals imported from Ghana. I am not aware of any deaths with this outbreak.

“The infection is primarily spread through physical contact with either an infected animal or person and gains entry to the body through breaks in the skin or through the conjunctive of the eye.

“It had been thought that person to person transmission was quite low <10% for household contacts. However, in a recent outbreak in the Democratic Republic of Congo there was sustained person to person transmission2 with a household attack rate of up to 50%. It is now known that there appear to be two main types of the virus. One “Congo Basin” type which causes more disease, higher death rates and more transmissible from person to person.  The other is the “West African” type which is less transmissible and causes less severe disease and fewer deaths3.

“There is no effective treatment and most cases will recover by themselves. It does appear that smallpox vaccine is also effective against Monkeypox, though of course not many of the UK population will have had smallpox vaccine during the past five decades. In my view the earlier low reported transmission rates even in the Congo could be because of more recent smallpox the 1980s in Africa whereas very few people have had this vaccination in recent decades.

“Because these cases are being reported as the West African type it is unlikely that we will see particularly severe disease or that we would see sustained community transmission in the UK.”

  1. Brainard J, Hunter PR. Misinformation making a disease outbreak worse: outcomes compared for influenza, monkeypox, and norovirus. Simulation. 2020 Apr;96(4):365-74.
  2. Nolen LD, Osadebe L, Katomba J, Likofata J, Mukadi D, Monroe B, Doty J, Hughes CM, Kabamba J, Malekani J, Bomponda PL. Extended human-to-human transmission during a monkeypox outbreak in the Democratic Republic of the Congo. Emerging infectious diseases. 2016 Jun;22(6):1014
  3. Beer EM, Rao VB. A systematic review of the epidemiology of human monkeypox outbreaks and implications for outbreak strategy. PLoS neglected tropical diseases. 2019 Oct 16;13(10):e0007791.


Dr Simon Clarke, Associate Professor in Cellular Microbiology, University of Reading, said:

“Monkeypox was first discovered in monkeys in the 1950s but by 1970 it had spread to humans.  It’s also found in other wild animals like some rodents, so monkeys may not be the main natural reservoir for the virus.  Transmission to humans is presumed to be due to eating infected animals. 

“Monkeypox is caused by a virus which is very similar to smallpox and the characteristic lesions on the skin look similar.  Illness usually lasts 2-4 weeks and it’s been estimated that the West Africa strain, which the UK cases have, has a mortality rate of about 1%. There is also a strain found in the Congo region which can be fatal in as many as 10% of cases, but the UK cases do not have this strain.

“There is currently a monkeypox vaccine under development, but smallpox vaccine and treatments could be deployed to control any monkeypox outbreak, but we don’t know how successful that might be because it’s never been tried.

“Humans can become infected by contact with an infected animal, human or materials which are contaminated with the virus.  Virus enters the body through breaks in the skin, some of which may not be visible and by eyes, mouth nose or other parts of the respiratory tract, which is thought to be the primary source or person-to-person contact.”


Prof Jimmy Whitworth, Professor of International Public Health, London School of Hygiene & Tropical Medicine (LSHTM), said:

“This outbreak of monkeypox is unprecedented in the UK and has provoked urgent public health action. There is a need to engage with the at-risk community of gay and bisexual men to ensure they know about the presence of this infection and report any sign and symptoms to health facilities. Cases need to be identified, isolated and treated, either in hospital or at home, depending on severity and circumstances. Close contacts need to be identified and monitored for signs of infection. Monkeypox is not very transmissible and with these measures the outbreak can be quickly brought under control.

“Monkeypox is a viral infection usually seen in forested areas in west and central Africa. It is spread by small mammals and can affect people living in rural areas who come into contact with them. It will have been brought to the UK recently by a traveller from west or central Africa who was incubating the infection. It spreads by close contact, either through touching the person, or items such as bedding or shared utensils. It can cause serious illness, although most people recover fully within a few weeks. Treatment is generally supportive as there are no specific drugs available. However a vaccine is available that can be given to prevent the development of disease.


Dr Michael Head, Senior Research Fellow in Global Health, University of Southampton, said:

“We do see occasional imported cases of monkeypox into the UK, and have previously seen human-to-human transmission. Case numbers remain very small, as it’s a hard virus to transmit between humans. It needs very close contact, for example skin to skin contact with an individual who is infectious with a monkeypox rash. Between these new cases, there will have been that close contact.

“There’s currently gaps in our knowledge, and the contact tracing and public health investigation being carried out by UKHSA will no doubt reveal more in due course, for example about how pattern of transmission. However, it would be very unusual to see anything more than a handful of cases in any outbreak, and we won’t be seeing covid-style levels of transmission.

“Whilst part of a different family of viruses, a pragmatic comparison might be to suggest that this virus behaves in a similar fashion to Lassa Fever, where we saw a few cases here in the UK earlier in 2022, tragically with an associated death; however, the outbreak did not spread more widely.

“Monkeypox can be a serious infection, with mortality rates from this type of monkeypox virus having been around 1% in other outbreaks. These are often in lower-income settings with limited access to healthcare. Here, the risks to the wider UK public are extremely low, and we do have healthcare facilities that specialize in treating these tropical infections. However, with tropical medicine, these imported cases do indicate a wider burden of disease elsewhere in the world. It may be that in a post-pandemic environment, we should be giving more consideration to understanding the local and global implications of Lassa, monkeypox, Ebola and other rare but serious pathogens.”

Ref – exporting of monkeypox cases paper, includes mention of UK human to human transmission –



Declared interests

Dr Mike Skinner: “No conflicts to declare.”

Prof Jimmy Whitworth: “My wife is employed by UKHSA.”

None others received.

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