Research and analysis

Qualitative assessment of the risk to the UK human population of mpox infection in a canine, feline, mustelid, lagomorph or rodent UK pet

Updated 20 March 2025

About the Human Animal Infections and Risk Surveillance group

This document was prepared by the UK Health Security Agency (UKHSA) on behalf of the joint Human Animal Infections and Risk Surveillance (HAIRS) group.

HAIRS is a multi-agency cross-government horizon scanning and risk assessment group, which acts as a forum to identify and discuss infections with potential for interspecies transfer (particularly zoonotic infections).

Members include representatives from:

• UKHSA
• Department for the Environment, Food and Rural Affairs (Defra)
• Department of Health and Social Care (DHSC)
• Animal and Plant Health Agency (APHA)
• Food Standards Agency (FSA)
• Food Standards Scotland (FSS)
• Public Health Wales
• Welsh Government
• Public Health Scotland
• Scottish Government
• Public Health Agency of Northern Ireland
• Department of Agriculture, Environment and Rural Affairs for Northern Ireland
• Department of Agriculture, Food and the Marine
• Health Service Executive, Republic of Ireland
• Infrastructure and Environment, Government of Jersey
• Isle of Man Government
• States Veterinary Officer, Bailiwick of Guernsey

Information on the risk assessment processes used by the HAIRS group can be found at HAIRS risk assessment process.

Version control

Date of this assessment: 10 March 2025

Version: 3.0

Reasons for the assessment: reports of human-to-human transmission of mpox virus in the UK; concerns for pets in the homes of infected people.

Reason for update: to account for the new epidemiology and spread of clade I mpox.

Completed by: HAIRS members.

Non-HAIRS group experts consulted: Dr. Lorraine McElhinney, Dr. Pip Beard.

Date of initial risk assessment: 22 May 2022, 30 August 2022.

Information on the risk assessment processes used by the HAIRS group can be found online.

Summary

There are 2 clades of monkeypox virus (MPXV):

• clade I (formerly known as Central African or Congo Basin clade), which can be further categorised into clades Ia and Ib
• clade II (formerly known as West African clade), which can be further categorised into clades IIa and IIb, which contain subgroup clusters called lineages

The risk of new introductions of MPXV to the UK depends on the extent of the circulation of the virus in other countries. MPXV transmission may also occur when a person comes into close contact with an infected animal (rodents are believed to be the primary animal reservoir for transmission to humans), or materials contaminated with the virus. MPXV has not been detected in animals in the UK to date.

During a previous mpox incident in the UK in 2018, a pet management process had to be swiftly implemented for one affected household, without conducting a risk assessment a priori.

In May 2022, human-to-human transmission of clade II MPVX was observed in several non-endemic countries, including the UK.

As the numbers of affected households in the UK related to the 2022 outbreak rapidly increased, this warranted a thorough assessment of the risk posed by mammalian pets exposed to MPXV to people with whom they may subsequently have come into contact. Clade II mpox cases continue to be reported globally.

Since 2023, there have been growing outbreaks of clade I MPXV, affecting Central and East African countries. Since August 2024, clade Ib mpox cases in humans have been reported outside of the African Region for the first time. On 14 August 2024, the World Health Organization determined that the upsurge in clade I mpox cases constituted a Public Health Emergency of International Concern. A travel-associated case of clade Ib mpox was detected in the UK on 30 October 2024 and further imported clade Ib mpox cases in the UK have been reported since then. It is possible future incursions of clade I mpox may occur in the UK, which could result in household transmission where pets are present.

This assessment considers the scenario where a mammalian pet is present in the household of a confirmed human mpox case. The transmission risk posed by the human case is to the non-infected human contacts, to other domestic or companion animals (who if infected could possibly then spread infection to non-infected humans in the household), or to in-contact peridomestic or wild rodents. With regard to mammalian pets, it is concluded that the highest risk of transmission is to pet rodents if present - more so than to lagomorphs, canids, felids and mustelids.

It is unlikely (but cannot be ruled out) that an infected rodent pet could subsequently spread infection to peridomestic or wild rodents. As rodents may not show clinical signs of infection, and the incubation period is unknown, testing to detect the presence of antibodies as well as virus would provide more confidence in ruling out infection.

The evidence of susceptibility for non-rodent pets is poor or incomplete, and therefore a precautionary risk management process should be considered.

Based on current evidence for pet rodents of susceptible species in households where there are infected people, placement in secure accommodation within the household (keeping the rodent in a cage where they cannot be accessed by people from outside the household) for a limited quarantine or isolation period (21 days) and testing to exclude infection if animals develop clinical symptoms is recommended. This is particularly important where there are infected human contacts who have had close and prolonged contact with the animal or its bedding and/or litter and where there are clinically susceptible individuals still present in the household. Testing is likely to include swabbing of the animal and sampling of its cage, bedding and/or litter.

Appropriate risk management for laboratory staff handling samples, or vets and animal health professionals handling or taking samples from the pets, should also be established. MPXV is categorised by the Advisory Committee on Dangerous Pathogens (ACDP) as a Hazard Group 3 biological agent meaning that it can cause severe human disease and may be a serious hazard to employees. According to the Health and Safety Executive, veterinary practices should conduct thorough risk assessments, implement effective control measures for hazards like animal handling and veterinary medicines, and ensure staff are properly trained and equipped for safety.

Assessment of the risk of infection from infected animals to the human population in the UK

Probability of infection for general population: Very low.

Probability of infection for individuals interacting with infected pets (notably rodents) and their contaminated environments: Moderate to high.

Impact: Low (for general population) to moderate (for individuals interacting with infected pets (notably rodents) and their contaminated environments).

Level of confidence in assessment of risk

Satisfactory.

Evidence is incomplete for the susceptibility of endemic UK rodent populations to MPXV infection (both clades). There is evidence for non-native rodent susceptibility and limited or no evidence for susceptibility of non-rodent mammalian pets. There is some evidence from previous outbreaks of animal-to-animal transmission or rodent-to-human transmission.

Actions and/or recommendations

Owners should ensure rodent pets of susceptible species in an affected household have access to secure accommodation (keeping the rodent in a cage where they cannot be accessed by people from outside the household), where the animal is maintained for 21 days. If the animal has shown clinical signs in that period, owners should contact their private vet to discuss if a negative (PCR) test should be undertaken for the animal before release from the secure accommodation.

Other mammalian pets should be kept under household isolation as far as possible, avoid direct contact with other animals outside the household and be regularly observed by their owner for clinical signs of infection (fever, skin lesions, respiratory signs). If anything is observed, pet owners should call their private vet for advice.

This risk assessment addresses:

• the overall likelihood that an animal will become infected with MPXV through close direct and prolonged contact in a household with an infected human, and that this could then become a vehicle for further human infections
• the assumption that the naïve animal has already had contact with a known human confirmed case and subsequently became infected, and how this depends on the species of animal, the nature of the animal or human contact, the clinical severity of the human case and/or level of contamination in the environment
• the risk pathways for onward transmission to humans, which could cover direct contact between a naïve human and the infected pet, or an infected pet in contact with wild, peridomestic or domestic rodents or companion animals which then become a source of infection for humans
• this risk assessment does not address human-to-human transmission of MPXV, which is considered in UKHSA’s technical briefings

Step 1. Assessment of the probability of infection in the UK human population

This section of the assessment examines the likelihood of an infectious threat causing infection in the UK human population. Where a new agent is identified there may be insufficient information to carry out a risk assessment and this should be clearly documented. Please read in conjunction with the probability algorithm found at Annexe A.

In this circumstance, we are assuming MPVX infection is already present in a person owning a pet in the UK, and that the pet may become infected, giving rise to more human cases.

Transmission is likely to be via close contact with the infected animal (bites, scratches, respiratory droplets) or contaminated fomites in the household setting. We are considering the susceptibility of the pet species involved, and not the likelihood of the pet becoming infected from the infected human and/or contaminated environment.

Is this a recognised human disease?

Outcome: Yes.

Quality of evidence: Humans: Good. Rodents: Satisfactory. Other species: Poor.

Mpox is a zoonosis that can cause human illness clinically indistinguishable from smallpox (1). It is caused by the monkeypox virus (MPXV), which is an orthopoxvirus that is genetically distinct from other members of the Poxviridae family, including the variola, vaccinia, ectromelia, camelpox, and cowpox viruses. It was first identified as the cause of a pox-like illness in captive monkeys at the State Serum Institute in Copenhagen in 1958 (2).

Mpox is regarded as the most important orthopoxvirus infection in human beings since the eradication of smallpox (3) By contrast with variola virus, however, MPXV has a wide range of hosts (4), which has allowed it to maintain a reservoir in wild animals while sporadically causing human disease (5). It therefore cannot be eradicated by human vaccination alone, although it may be possible to be controlled by targeted vaccination of humans (using a smallpox vaccine, which is approved for use against mpox) and culling animal reservoirs in certain circumstances.

The first human case of mpox was recorded in 1970 in the Democratic Republic of the Congo (DRC) (6), and since then the infection has been reported in a number of African countries, where it is considered endemic. Prior to 2022 most human cases are reported from the DRC and Nigeria, with clusters of cases occasionally being reported in Central African Republic (CAR).

Sporadic cases were also reported in Cameroon, Gabon, Côte d’Ivoire, Liberia, the Republic of the Congo, Sierra Leone, and South Sudan (7 to 12).

There are 2 clades of MPXV:

• clade I (formerly known as Central African or Congo Basin clade), which can be further categorised into clades Ia and Ib
• Clade II (formerly West African clade) which can be further categorised into clades IIa and IIb, which contain subgroup clusters called lineages. Most mpox cases observed in the 2022 outbreak were clade IIb, lineage B.1 MPXV (13)

The case fatality rate (CFR) can vary between less than 1% and 10%, but it is clade dependent with clade II causing lower mortality (5).

Since 2023, there have been growing outbreaks of clade I MPXV, affecting Central and East African countries. Most cases have been reported from the DRC. In March 2023, a cluster of clade I MPXV-associated infections linked to sexual contact was reported in the DRC for the first time (14). Transmission was confirmed amongst male partners, and simultaneously through heterosexual transmission in outbreaks occurring in different geographic areas. In 2024, geographic differences in demographic characteristics and viral genetic diversity suggest multiple transmission modes (for example, zoonotic, household and/or sexual) in different provinces in the DRC. Reports of clade I MPXV transmission through sexual contact have continued, particularly in DRCs South Kivu Province (15). Sequencing of samples from cases in January 2024 identified a highly divergent clade I virus, subsequently designated as clade Ib (16), which is estimated to have emerged around mid-September 2023. This new sublineage predominantly exhibited APOBEC3-type mutations, suggesting viral adaptation due to sustained circulation among humans (17).

Since the end of August 2024, geographical expansion of the clade Ib outbreak has been observed, with community transmission occurring in neighbouring DRC countries including Burundi, Uganda and Rwanda for the first time. Confirmed clade Ib cases have also been reported from Kenya, Zambia and Zimbabwe (18). Outside of the African Region, and as of 17 January 2025, travel associated clade Ib mpox cases have been reported from Germany (19), India (20), Sweden (21), Thailand (22), the United States (23), Canada (24), Belgium (25), Oman (26), Pakistan (26), France (27), China (28) and the UK (29). See below for details.

In 2003, a large outbreak of human cases of clade II mpox was detected in the USA, which was associated with the importation of pet rodents from West Africa. Laboratory testing by the US Centers for Disease Control and Prevention (CDC) showed that 2 African giant pouched rats, 9 dormice and 3 rope squirrels were infected with MPXV.

After importation into the USA, some of the infected animals were housed near prairie dogs at the facilities of an Illinois animal vendor. These prairie dogs were sold as pets before they developed signs of infection. Consequently, there were 47 confirmed and probable human cases (no deaths), and no human-to-human transmission was reported (30).

During the clade II mpox outbreaks, there were 2 suspected cases in pet dogs, one in Brazil and one in France. However, there is still some uncertainty about whether the animals were truly infected or had a contaminated skin lesion (31, 32). Nevertheless, there is evidence for certain animal species being susceptible to infection, including giant pouched rats, chinchillas, squirrels, marmots and prairie dogs (33), therefore this risk assessment focuses more on keeping rodents as companion animals.

Is the disease endemic in humans in the UK?

Outcome: No.

Quality of evidence: Good.

Mpox is not an endemic disease in the UK. Prior to 2022, 7 cases of mpox had been reported (all clade II) in the UK, all of which were, or were linked to, travel associated cases. In 2018, 2 cases of mpox were identified in the UK in individuals who had travelled from Nigeria (31). The cases were epidemiologically unconnected.

A third case was diagnosed with mpox, following contact with contaminated bed linen. The case was a healthcare worker involved in the care of one of the previous cases (32). In 2019, an individual in England was confirmed to have mpox after recently travelling from Nigeria.

In May 2021, a case of mpox was identified in Wales, also with a travel history from Nigeria. In this incident, 2 family members were subsequently identified as having mpox and all 3 cases recovered (33).

On 7 May 2022, the UK Health Security Agency (UKHSA) announced a confirmed case of mpox in an individual with a travel history to Nigeria (34). The case developed a rash on 29 April 2022 and arrived in the UK on 4 May 2022, having departed Nigeria on 3 May 2022. Extensive contact tracing was undertaken to identify and follow-up exposed contacts of the case in healthcare settings, the community and the international flight. The clade was not specified.

On 14 May 2022, 2 mpox cases were identified in London who were not linked to the case reported on the 7 May 2022 (34). The clade was not specified.

Four new cases were identified on the 16 May 2002, 3 in London and 1 case in the North East of England (34). None of these cases had known links to those reported on the 7 and 14 May 2022 and there was no link to travel to a country where mpox was considered endemic.

Genomic sequencing confirmed the cases were infected with the clade II of the virus (34), and these cases were considered the starting point of the UK’s 2022 outbreak, which predominantly affected gay, bisexual and men who have sex with men. Up to 31 December 2022, 3,732 clade IIb mpox cases were reported in the UK. Of these, 3,553 cases were reported in England, 34 in Northern Ireland, 97 in Scotland and 48 were in Wales. Clade IIb mpox cases have continued to be reported in the UK during 2023 and 2024, albeit at low levels. In 2023 and 2024, 429 clade IIb mpox cases were reported in the UK, of which a high proportion are considered travel associated (35).

On 30 October 2024, an imported case of clade Ib mpox was reported in England, in an individual who had recently travelled to countries in Africa experiencing clade Ib mpox cases. Three additional cases were reported amongst household contacts of the first case (29). This is considered the first secondary transmission of clade Ib mpox outside of the Africa region. Further imported cases of clade Ib mpox have since been reported in the UK (29).

Is the disease endemic in animals within the UK?

Outcome: No.

Quality of evidence: Good.

There have been no detections of MPXV in wild, domestic or peridomestic animals within the UK.

Are there routes of introduction into animals in the UK?

Outcome: Yes.

Quality of evidence: Satisfactory.

The risk of new introductions of MPXV to the UK depends on the extent of the circulation of the virus in other countries.

Given the geographical expansion of countries now reporting confirmed cases of mpox (notably clades Ib and IIb) and community transmission in some of these countries – the extent of which is under investigation – then new travel-associated cases in the UK cannot be excluded.

The risk to the UK public would come from a human case of mpox being imported into the UK, which is dependent on the number of travellers expected from affected countries and direct, rapid travel routes, or from the importation of an infected animal reservoir.

The movement of primates or rodents for commercial reasons or as pets into Great Britain is regulated by the Rabies Import Order (The Rabies (Importation of Dogs, Cats and Other Mammals) Order 1974), and the Rabies (Importation of Dogs, Cats and Other Mammals) Order (Northern Ireland) 1977, which would require all animals to undergo 4 months quarantine (3 months in Scotland) in a rabies-approved quarantine kennel after entry, unless prepared for pet travel (for example, have been microchipped, have a pet passport or health certificate, are vaccinated against rabies) or a derogation is applied (such as for approved establishments like zoos).

Commercial movements from Europe and their large exotic pet markets may be undertaken under licence and do not require a health certificate. Quarantine establishment kennels are not necessarily rodent ingress proof, but are designed to prevent the escape or deliberate release of animals and to manage transmission of rabies between those animals present. The illegal trade in such ‘exotic’ pets is difficult to quantify but seizures are made at the UK border, and these animals are moved to approved quarantine establishments.

There are evidence gaps around the infectious period or incubation period in animals, but the indirect transmission pathways via contaminated bedding or animal cages should not be discounted, given the persistence of pox viruses in the environment in general.

Are effective control measures in place to mitigate against these routes of introduction?

Outcome: Humans: Yes. Rodents and non-rodent mammalian animals: No.

Quality of evidence: Satisfactory.

Human-to-human transmission may occur through contact with clothing or linens (such as bedding or towels) used by an infected person, direct contact with mpox skin lesions or scabs (including during sexual and intimate contact), or through contact with bodily fluids such as saliva, nasal secretions or mucus of an infected person (5). Although evidence is limited, it may be possible that clade I MPXV may transmit between individuals through close and prolonged face-to-face contact such as talking, breathing, coughing, or sneezing if they have lesions in their throats (36).

Preventing direct contact is therefore the most appropriate control measure. Human cases can be treated and ring vaccination (using smallpox vaccine) of contacts can be applied. After infection, and once the scabs have dried up, the patient is no longer infectious and there is a strong immune response.

Effective decontamination of the environment frequented by a person with mpox is also necessary (37). Whilst the virus (enveloped DNA virus) is highly resistant in the environment to temperature, it can be destroyed with detergents.

In the UK there are established processes for the isolation of clade I mpox cases, rapid diagnostics, and infection prevention and control within healthcare settings aimed at mitigating the risk of further transmission (38).

MPXV transmission may also occur when a person comes into close contact with an infected animal (rodents are believed to be the primary animal reservoir for transmission to humans), or materials contaminated with the virus. MPXV has not been detected in animals in the UK to date.

While there are no health certificates required unless the animals are destined for approved or confined establishments, there are border checks which do sometimes identify illicit or illegal trade and where this occurs, the animals are removed to quarantine. The checks are not intended to identify sub clinical or asymptomatic infection; rather they are to check compliance with import certification. If infection is present in small mammals which are imported as part of the exotic pet trade from the European Union (EU), infected animals are unlikely to be identified via this route.

Otherwise, there are no harmonised health certificates for the commercial import of rodents into the EU from third countries, and MPX is not notifiable under the EU Animal Health Law Commission Implementing Regulation EU/2018/1882.

Once imported into the EU, animals would not be subject to quarantine on arrival in the UK, if the commercial documents are all in order. If they are declared as originating in a third country, then the animals may be subject to quarantine, depending on the country of origin and the place of destination. Exotic pet trade fairs are commonplace in the EU.

Therefore, susceptible rodent pets that were in direct close contact with an infected human should be isolated for a period equivalent to the human maximum incubation period of 21 days. Veterinary management of animal patients involves symptomatic treatment and supportive care, as required. While it is not clear what the clinical signs might be, it is expected that skin lesions, fever and respiratory signs should be monitored.

Do environmental conditions in the UK support the natural reservoirs or vectors of disease?

Outcome: Yes.

Quality of evidence: Satisfactory.

Various animal species have been identified as susceptible to MPXV. Rodents are considered natural reservoirs of infection, including rope squirrels, African ground squirrels, tree squirrels, Gambian pouched rats, and African dormice (39). Other natural reservoirs include non-human primates, such as sooty mangabeys (40) and chimpanzees (41). Other wild animals are also known to be susceptible, such as prairie dogs, chinchillas, marmots and groundhogs, but they are not present in an endemic country (34, 42).

Uncertainty remains concerning the natural history of MPXV and further studies are needed to identify the exact reservoirs and how virus circulation is maintained in nature. However, there is laboratory evidence of susceptibility for the red squirrel, Sciurus vulgaris (43) and for certain wild derived strains of Mus musculus, the house mouse.

Although there is no evidence of susceptibility of common endemic wildlife species in the UK to MPXV, rodents (including voles, dormice, rats, mice, and squirrels) as well as lagomorphs (rabbits and hares) and hedgehogs could all be considered potential reservoirs, based on field and laboratory observations (43, 44).

Investigating small animals such as rabbits, ground squirrels, prairie dogs, cotton rats, white rats, golden hamsters and guinea pigs as animal models for MPXV demonstrated varying levels of susceptibility depending on route of inoculation and age of the animal (46, 47).

Lack of clinical signs in infected adult white rats and white rabbits supports the theory that the clinical outcome will depend on the route of inoculation or age and immune status of the animals (45). This, coupled with potential for viral shedding and limited data on pathogenesis, provides low confidence in diagnostic predictive values using different sampling matrices or in the incubation period.

In 1979, a large-scale survey of animals (representing at least 43 species) in the DRC detected evidence of positive serology for Orthopoxviruses among non-human primates, as well as evidence of at least one species of terrestrial rodent, mainly squirrels, exhibiting presumed MPXV-specific reactivity (47). This was consistent with findings that about 12% of persons presumed to have been infected by contact with animals had recent contact with squirrels (48).

None of the domestic animals tested – 120 sheep and goats, 67 cats – exhibited serological evidence of Orthopoxvirus infection (49). In 1985, the isolation of MPXV from a captured, symptomatic squirrel (Funisciurus anerythrus) was made (47).

The only other instance of virus isolation from a wild animal was in 2012 from a juvenile sooty mangaby (Cercocebus atys) from Côte d’Ivoire (49).

The only other instances of virus isolation from a wild animal was in 2012 from a juvenile sooty mangabey (Cercocebus atys) from Côte d’Ivoire (40) and in a troop of chimpanzees (Pan troglodytes) in Côte d’Ivoire in 2017 (41).

Nearly all sub-species of the common house mouse, Mus musculus, are resistant to challenge with MPXV when adult animals with functional immune systems are used (46), (50).

One example of an exception to this is the castaneous (CAST) subspecies of the house mouse, Mus musculus castaneus, an in-bred wild strain used in experimental work, due to intrinsic low levels of IFN-γ and TNF-α responses and overall fewer NK cells and CD4+ and CD8+ T cells (51).

Outbreaks among captive animals on display or kept as pets reveal further evidence for the involvement of animals. During the clade II outbreak in 2022, infection was suspected in a dog in France (52) and a dog in Brazil (53), likely as a result of human-to-animal transmission following direct contact while the humans were symptomatic (though there is still some uncertainty about whether the animals were truly infected or had a contaminated skin lesion (54, 55)). The Brazilian dog showed mucocutaneous lesions which tested positive on PCR. These are the first documented cases of suspected human to animal transmission of MPXV, though there is still very high uncertainty about the susceptibility of common companion animals to mpox (55).

Historically, 2 New World giant anteaters (Myrmecophaga tridactyla) were infected with MPXV at the Rotterdam zoo outbreak in 1964, during which individuals from 7 different species of non-human primates became ill and in some cases died (56).

While anteaters are not considered to play a role in the natural lifecycle of MPXV, it is possible that transmission hosts need not be natural, maintenance hosts of the virus. Captive animals seem particularly vulnerable to the epizootic spread of MPXV, whether due to crowding, species mixing, or physiological stress, a fact underscored by 2 outbreaks at primate sanctuaries in Cameroon (57).

Under experimental conditions, susceptibility of rabbits to MPXV has been shown (58) and infection of an African hedgehog was confirmed in the 2003 USA outbreak (59). The susceptibility of wild or pet/captive Mustelidae to MPXV is unknown.

In 2003, in the USA, MPXV was introduced to several mid-western states through a consignment of African rodents (origin Ghana) destined for the pet trade (60). Local surveillance at the site of animal carcass disposal did not detect evidence of the virus in feral or wild rodent populations but infection did spread to domestic prairie dogs kept as pets in households.

Three genera of African rodent, Graphiurus, Cricetomys and Funisciurus (African dormice, giant pouched rat, rope squirrel, respectively) were implicated as vehicles of virus introduction during the initial importation event (58, 61).

Studies performed subsequently to assess the competence of each species to serve as natural reservoirs of the virus demonstrated that, in general, though none showed ‘tolerance’ (for example, virus amplification and shedding in the absence of evident disease), each was capable of being infected and of shedding viable virus for extended periods of time through varied routes (62 to 66).

There is no evidence to suggest there would be differences between clade I and clade II in terms of animal susceptibility.

Poxviruses, including MPXV, are very stable in the environment and therefore exposure of wild or pet rodents to household rubbish contaminated with mpox by infected humans, and subsequent risk of infection, cannot be excluded. Wildlife involvement was ruled out by wildlife surveillance around the cases in the USA in 2003, and surveillance around outbreaks in Nigeria have not found infected wild trapped rodents, but more research is needed in this area. An effective isolation period should therefore take into account the date from when the household has been decontaminated or the pet removed from the environment.

Will there be human exposure?

Outcome: General population: No. For individuals interacting with infected pets (notably rodents) and their contaminated environments: Yes.

Quality of evidence: Good.

MPXV enters the body through broken skin (even if the wound is not visible), respiratory tract, or the mucous membranes (eyes, nose, or mouth).

Animal-to-human transmission may occur when a person comes into close contact with the saliva, blood or other bodily fluids of an infected animal. If clinical signs, such as pustules and skin lesions are present, the process of desquamation can lead to environmental contamination.

Exposures may include being bitten or scratched by an infected animal, preparation of infected wild animal carcasses for consumption, or contact with a contaminated environment frequented by an infected animal (such as contaminated animal bedding, feeding bowls, water bottles).

Pet owners of fancy rats and other domestically kept rodents are usually in close contact with their pets, and their environments (for example housing, bedding, feeding materials). Based on transmission pathways of Hanta- (67) and Borna-viruses (68), there are known risk pathways for transmission, including cleaning cages.

During the 2003 outbreak in the USA, 37 people were infected as a result of contact with infected pet prairie dogs, which had contracted infection from contact with imported African rodents in a pet shop (69).

MPXV is an ACDP Category 3 pathogen, meaning it can cause severe human disease and may be a serious hazard to those handling and processing samples (for example healthcare workers, laboratory staff) if appropriate personal protective equipment is not worn.

Human-to-human transmission occurs through direct contact with body fluids or lesion material (including during sexual contact, kissing, cuddling or other skin-to-skin contact), indirect contact with clothing or linens (such as bedding or towels) used by an infected person and/or possibly through large respiratory droplets if lesions are present in their throat (these respiratory droplets generally cannot travel more than a few feet, and so prolonged face-to-face contact is required).

Are humans highly susceptible?

Outcome: For unvaccinated individuals: Yes.

Quality of evidence: Good.

Mpox is usually a self-limiting disease with symptoms lasting from 2 to 4 weeks. The illness is often mild and most of those infected will recover without treatment. Underlying immune deficiencies may lead to worse outcomes. Cases of severe disease can occur more commonly among children and are related to the extent of virus exposure, patient health status and nature of complications. Clade I MPXV is known to cause more severe disease than other MPXV clades and a case fatality rate of up to 10% in unvaccinated individuals has been reported during previous outbreaks (70, 71).

Analysis of case data during the 2022 global clade IIb outbreak indicates that the MVA-BN (Imvanex/JYNNEOS) vaccine (licensed for use in Canada, the USA, EU, UK and Switzerland) was effective in preventing mpox disease. In England, the estimated vaccine effectiveness against symptomatic mpox at least 14 days after a single dose was 78% (95% CI 54 to 89) among an at risk-population (72). Additionally, Berry et al. showed that delaying the second dose of MVA-BN vaccine provided more durable protection (73).

People vaccinated against smallpox in childhood may experience a milder disease. People younger than 40 to 50 years of age (depending on the country) may be more susceptible to mpox due to cessation of smallpox vaccination campaigns globally after eradication of the disease (routine smallpox vaccination ended in the UK in 1971 (74). Following the 2022 global clade IIb outbreak, gay, bisexual and other men who have sex with men who were eligible for vaccination are likely to have the highest levels of immunity to MPXV in the UK, due to the targeting of the vaccination strategy for protection against mpox. Outside of this target population, there is no data available to suggest that the general UK population would not be susceptible to MPXV.

The extent to which pre- or asymptomatic infection may occur is uncertain.

Is this disease highly infectious in humans?

Outcome: Yes/no.

Quality of evidence: Satisfactory.

People vaccinated against smallpox in childhood may experience a milder disease. Immunity in those who were vaccinated against smallpox would confer cross protection, but this population is declining in most countries. Following the 2022 global clade IIb outbreak, gay, bisexual and other men who have sex with men who were eligible for vaccination are likely to have the highest levels of immunity to MPXV in the UK, due to the targeting of the vaccination strategy for protection against mpox.

Generally, pox viruses do not have high reproductive rates and thus may not be considered highly infectious. Close contact with an infected human or animal is required for transmission to take place.

Infectiousness may be considered higher for individuals partaking in activities which would result in close skin contact or exposure to infectious air droplets and/or bodily fluids or material from desquamation (75).

Outcome of probability assessment of MPXV infection in the UK human population

The probability of human infection with MPXV in the general UK population is considered very low.

For naive individuals interacting with infected pets (notably rodents) and their contaminated environments, the probability would be considered moderate to high.

Step 2. Assessment of the impact on human health

The scale of harm caused by the infectious threat in terms of morbidity and mortality: this depends on spread, severity, availability of interventions and context.

Please read in conjunction with the impact algorithm found at Annexe B.

Is there human-to-human spread of this pathogen?

Outcome: Yes.

Quality of evidence: Good.

Human-to-human transmission of MPXV may occur through contact with clothing or linens (such as bedding or towels) used by an infected person, direct contact with mpox skin lesions or scabs (including during sexual or intimate contact such as kissing, cuddling or other skin-to-skin contact) and/or contact with bodily fluids such as saliva, nasal secretions or mucus of an infected person.

Human-to-human transmission may also occur through large respiratory droplets, which generally cannot travel more than a few feet, and so prolonged face-to-face contact with an infected person is required. Individuals that may have direct skin contact with an infected individual may have a greater exposure risk to mpox infection.

Is the UK human population susceptible?

Outcome: Yes.

Quality of evidence: Good.

See above evidence.

Does it cause severe disease in humans?

Outcome: Yes/no.

Quality of evidence: Satisfactory.

Mpox is usually a self-limiting disease with symptoms lasting from 2 to 4 weeks. The illness is often mild and most of those infected will recover without treatment. Disease usually begins with fever, myalgia, fatigue and a headache (76).

Within 1 to 5 days after the appearance of fever, a rash develops, often beginning on the face then spreading to other parts of the body. Lesions can also affect the mouth, genitals and anus. The rash progresses through different stages before finally forming a scab which later falls off.

An individual is considered contagious until all the scabs have fallen off and there is intact skin underneath. The scabs may also contain infectious virus material.

Severe cases occur more commonly among children (6) and are related to the extent of virus exposure, patient health status and the nature of complications. In endemic countries, complications include secondary infections, bronchopneumonia, sepsis, encephalitis, and infection of the cornea impeding vision (77).

Underlying immune deficiencies may also lead to worse outcomes. Disease severity is also dependent on the MPXV clade an individual is infected with.

Historically, clade I MPVX has caused more severe disease (CFR up to 10%) and may be more transmissible compared to clade II (CFR approximately 1%) (78, 79). There is some evidence that the severity of clade Ib infection is between that of clade I and clade II (80, 81).

Is it highly infectious to humans?

Outcome: Yes/no.

Quality of evidence: Satisfactory.

See above evidence.

Would a significant number of people be affected from zoonotic exposures?

Outcome: No.

Quality of evidence: Good.

Within the UK, well established and robust public health interventions are implemented in response to cases of mpox infection. This involves the isolation and treatment (if required) of suspected and confirmed mpox cases, and where appropriate extensive contact tracing designed at preventing further transmission.

Ring vaccination of humans, using the modified vaccinia Ankara (MVA-BN) (Imvanex/JYNNEOS) smallpox vaccine, has also been used in the UK in response to mpox incidents (82).

There is no requirement for pet rodents to be registered in the UK. Predicted numbers of pet rodents in the UK is based mainly on sales data for pet food and is estimated at around 1.9 million households (as opposed to 12 million dogs and 11 million for cats) (83). There is no reliable data for imports of ‘exotic pets’.

As most pet rodents are kept in cages within the household, and may be handled frequently, the level of exposure to owners is likely to be high, but less so for visitors or household members who are not comfortable with handling small mammals. Therefore, the level of exposure at the population level is considered low.

Contact with peridomestic rodents (house mice predominantly, but rats are commonly found in urban settings) cannot be excluded for any household with pet rodents. Therefore, there would be a potential exposure route for peridomestic rodents, but these animals are even less likely to have close direct contact with a human. Nevertheless, the transmission pathways for wild animals to humans have not been fully elucidated and contact with contaminated surfaces cannot be ruled out.

Are effective interventions (preventative or therapeutic) available?

Outcome: Yes.

Quality of evidence: Good.

There are no vaccines or treatments that have been developed specifically for mpox. Clinical care for mpox is mainly supportive. Patients should be offered fluids and food to maintain adequate nutritional status and secondary bacterial infections should be prevented and treated (6).

Specific antiviral medications such as Tecovirimat and Cidofovir have been used in the treatment of mpox, particularly for severe cases or individuals at higher risk of complications. However, whilst Tecovirimat has been shown to have in vitro activity against mpox, there is currently no randomised control trial data to support its use. There are also genomic and phenotypic data to suggest the emergence of resistant phenotypes for clade IIb MPXV 84).

Analysis of case data during the 2022 global clade IIb outbreak indicates that the MVA-BN (Imvanex/JYNNEOS ) vaccine was effective in preventing mpox disease. Whilst most MVA-BN vaccine studies are associated with clade IIb MPXV, it is presumed that available vaccines will provide cross-protection against clade I MPXV (85). A major plank of the basis of licensing was primate protection studies, which were undertaken using clade I viruses. There is no data on effectiveness of MVA-BN vaccine for clade I MPXV, but previous studies in the DRC in people who received replicating smallpox vaccination and T-cell epitope mapping between clade I and clade IIb suggests that there should be some cross-reactivity and protection (86, 87).

Appropriate isolation of suspected and confirmed mpox cases is essential for preventing transmission. In the UK there are established processes for the isolation of clade I mpox cases, rapid diagnostics, and infection prevention and control within healthcare settings aimed at mitigating the risk of further transmission (38).

Mpox pustule scabs are also infectious and care must be taken to avoid infection through handling contaminated clothing or linen (such as bedding or towels) that has been used by an infected person (irrespective of clade). Individuals cleaning or decontaminating rooms that a patient with mpox has spent significant time in should wear appropriate personal protective equipment to avoid direct contact with contaminated material during the decontamination process (37).

Isolation of pets to prevent further contacts with uninfected people should be applied to non-rodent pet animals as a precaution, and provided the welfare of the animal is not compromised. However, where there are rodent pets present, the evidence base is stronger that they can contribute to MPXV spread amongst rodents and to people in direct contact (75).

Rodent pets that have been exposed to the virus in a contaminated household should not be handled directly and should be prevented from contact with any wild or peridomestic rodents. Isolation in secure accommodation of such pets (for example, remaining confined to their cage and the use of appropriate PPE during necessary cleaning and care) should be advised by the private veterinary surgeon and guidance from APHA.

Outcome of impact assessment of MPXV infection in the UK human population

The impact of mpox infection in a canine, feline, mustelid, lagomorph or rodent UK pet on human health in the UK is considered low to moderate.

This is based on the assumption that disease is already present in the human population and there is no evidence to suggest with such limited pet to human contact of such small numbers, this would drive the evolution of mpox to strains with a greater pathogenicity.

Annexe A. Assessment of the probability of infection in the UK population algorithm

Accessible text version of Annexe A

Outcomes are specified by a ☑ (tick) beside the appropriate answer.

Question 1. Is this a recognised human disease?

Yes: go to question 3 ☑

No: go to question 4.

Question 2. Is this a zoonosis or is there zoonotic potential?

Yes: go to question 3.

No: the probability of infection in UK population is very low.

Question 3. Is this disease endemic in humans in the UK?

Yes: go to question 7.

No: go to question 4 ☑

Question 4. Is this disease endemic in animals in the UK?

Yes: go to question 8.

No: go to question 5 ☑

Question 5. Are there routes of introduction into animals in the UK?

Yes: go to question 6 ☑

No: the probability of infection in UK population is very low.

Question 6. Are effective measures in place to mitigate against these?

Yes: the probability of infection in UK population is very low.

No: go to question 7 ☑

Question 7. Do environmental conditions in the UK support the natural vectors of disease?

Yes: go to question 8 ☑

No: the probability of infection in UK population is very low.

Question 8. Will there be human exposure?

Yes: individuals interacting with infected pets (notably rodents) go to question 9 ☑

No: the probability of infection in general UK population is very low ☑

Question 9. Are humans highly susceptible?

Yes: go to question 10 ☑

No: the probability of infection in UK population is low.

Question 10. Is this disease highly infectious in humans?

Yes: the probability of infection in individuals interacting with infected pets (notably rodents) is high. ☑

No: the probability of infection in individuals interacting with infected pets (notably rodents) is moderate. ☑

Annexe B. Assessment of the impact on human health algorithm

This question has been added to differentiate between those infections causing severe disease in a handful of people and those causing severe disease in larger numbers of people. ‘Significant’ is not quantified in the algorithm but has been left open for discussion and definition within the context of the risk being assessed.

Accessible text version of Annexe B

Outcomes are specified by a ☑ (tick) beside the appropriate answer.

Question 1. Is there human-to-human spread?

Yes: go to question 4 ☑

No: go to question 2.

Question 2. Is there zoonotic or vector borne spread?

Yes: go to question 3.

No: the impact on human health in the UK is very low.

Question 3. For zoonoses or vector-borne disease, is the animal host or vector present in the UK?

Yes (animal host): go to question 4.

No (vector): impact on human health in the UK is very low.

Question 4. Is the human population susceptible?

Yes: go to question 5 ☑

No: the impact on human health in the UK is very low.

Question 5. Does it cause severe disease in humans?

Yes (immunocompromised individuals): go to question 8 ☑

No: go to question 6 ☑

Question 6. Is it highly infectious to humans?

Yes: go to question 9 ☑

No: go to question 7 ☑

Question 7. Are effective interventions available?

Yes: the impact on human health in the UK is very low ☑

No: the impact on human health in the UK is low

Question 8. Would a significant number of people be affected?

Yes: go to question 10.

No: go to question 9 ☑

Question 9. Are effective interventions available?

Yes. For individuals in contact with an infected pet, effective interventions such as reducing exposure to the pet or its bedding, and preventing the pet coming into contact with other animals by isolating the pet may prevent onward transmission. As it is likely the pet will be in the household of an infected person, vaccination of the humans present may also have been used to prevent spread. There may be no other uninfected people in contact. The impact on human health in the UK is low.

No. Effective interventions may not be available for a small number of people. Clinical signs may not be present in the pet and there may be unknown peridomestic animals present in the household. People in contact with the infected animals outside the household may not have been vaccinated or been made aware of the contact with an infected person or subclinical infection of the animal. The impact on human health in the UK is moderate.

Question 10. Is it highly infectious to humans?

Yes: go to question 12.

No: go to question 11.

Question 11. Are effective interventions available?

Yes: the impact on human health in the UK is moderate.

No: the impact on human health in the UK is high.

Question 12. Are effective interventions available?

Yes: the impact on human health in the UK is high.

No: the impact on human health in the UK is very high.

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