As the current international monkeypox outbreak in people continues, more consideration is being given to the potential impact on, and subsequently from, animals. Animals are the reservoirs for this virus, although there are lots of gaps in our knowledge of the species monkeypox virus can infect.

The current cases outside of Africa are being spread from human-to-human. Controlling this in people will therefore hopefully contain the outbreak. However, we have to consider the risk of spillback into animals (particularly wild animals) and the potential to establish animal reservoirs of the virus outside of Africa. Based on what we know, the primary concern would be infection of rodents, but we don’t know enough to say which species are of “no” concern when it comes to monkeypox.

Best case scenario:

• This is a weird outbreak caused by a lot of human-to-human transmission, but it will be contained and die out with the current surveillance and control measures.

Worst case scenario:

• Monkeypox is spread from infected people to new animal species outside of Africa, and an animal reservoir is created in countries where the virus has not been present previously. The virus could then be maintained in animals in these countries long term, with periodic spread back to people.

The best case scenario is most likely here, and that’s what we’re hoping for. However, it’s pretty dumb and dangerous to use a hope-based approach to infection control, so we still need to assess the risks of spread to (and then from) animals, and take reasonable precautions to control the risks as needed. In the interim, we should use some common sense measures to reduce the risk of human-to-animal spread. It’s better to use easy control measures early (even if they ultimately are found to be unnecessary) than to look back 6 months from now and say “crap… doing some things a few months ago would have really made a difference.”

Risk assessments are regularly done for emerging threats. I was involved in a couple of Canadian rapid risk assessments for SARS-CoV-2 in animals, and those provided useful information and discussion. The UK has just released their own qualitative assessment of the risk to the UK human population of monkeypox infection in a canine, feline, mustelid, lagomorth or rodent UK pet.  More concisely, I’d call it their “rapid assessment of the risk of spillback of monkeypox into selected domestic species.”

The assessment looks at what are likely the highest risk pet animal groups (rodents and rabbits (lagomorphs) and ferrets (mustelids)) and the most common pets (dogs/cats), but it doesn’t cover all species.  Of note, it doesn’t address pigs (commercial or pet) and there are questions about susceptibility of that species. However, it’s a pretty logical approach overall, particularly when it needs to be done rapidly.  A lot of the assessment and recommnedations are just good, common sense, and use of the precautionary principle in a controlled manner that doesn’t over-react.

Here are some highlights from the assessment:

As the numbers of affected households in the UK related to the current outbreak are rapidly increasing, this warrants a more thorough assessment of the risk posed by mammalian pets exposed to monkeypox virus to people with whom they may come into contact.

• Absolutely. We need to assess this as the outbreak continues and not rely on the somewhat limited data we have from past studies and outbreaks.

For the purposes of the assessment, it is presumed the pet is present in the contaminated household of a confirmed human monkeypox case. The risk posed is therefore to the non-infected human contacts or in-contact peridomestic or wild rodents. It is concluded that the highest risk is posed by the presence of pet rodents, more so than lagomorphs, canids, felids and mustelids.

It is unlikely (but cannot be ruled out) that an infected rodent pet could 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.

• This is a really important statement. Too often (and COVID-19 showed us this yet again), the early response by some groups is to say “there’s no evidence of a concern” and therefore no action required.  However, with an emerging disease, you sometimes have to act before there’s time to collect the evidence. By the time you know definitely that there can be spread to/from animals, it might be too late to control or prevent it.

Based on current evidence, for pet rodents in households where there are infected people, temporary removal from the household for a limited quarantine period (21 days) and testing to exclude infection is recommended, particularly where there are infected human contacts who have had close direct and prolonged contact with the animal or its bedding and/or litter.

• I disagree with this one. It’s good that the risk is being taken seriously. It’s good to consider testing (but we don’t know the sensitivity of testing, so it can’t be used to declare an animal uninfected). But does removing the animal help? It’s great that they clearly said “temporary removal,” so there’s no ambiguity that this might mean people should surrender or euthanize exposed animals. However, I wonder if removal of the pet really helps in a household where there’s been an infected person present, where the animal can be caged and where basic infection control practices aren’t hard to use during a quarantine period.
• Furthermore, does moving the animal create risk somewhere else, where there was no risk before? We had the same questions when SARS-CoV-2 emerged and we quickly settled on keeping pets in their infected households as the best solution.
• Making sure there’s no potential exposure of pet rodents to wild rodents is important, and if there’s a rodent infestation of the house, I’d be more inclined to want to get pet rodents out, to reduce the risk of human-to-pet-to-wild rodent transmission.  But taking care of the rodent infestation itself would also be critical to avoid direct human-to-wild rodent transmission.

Are effective control measures in place to mitigate against these routes of introduction? Outcome: yes – humans; no – rodents and non-rodent mammalian animals.

• This gets into the human control approaches that include smallpox vaccination, as well as lack of control measures in the UK for rodents imported from the EU that might introduce the virus.  So it’s true, but “no” isn’t necessarily what I’d say, since there’s always something we can to do mitigate risk. We have easy measure to reduce the risk, and those focus on restricting contact between infected people and their pets.

Do environmental conditions in the UK support the natural reservoirs or vectors of disease? Outcome: yes. Quality of evidence: satisfactory.

• This is a nice section. It’s long so I won’t copy it here but if you’re interested, check out the link for a good review of species susceptibility info.

I’ve wondered what countries were going to do a rapid risk assessment about spillback (I’ve also asked whether we’re going to do one here in Canada). The good news is that the vast majority of the content from the UK’s report would apply here and elsewhere. We have some differences in the types of wildlife that are present in Canada, but the overall risks, control measures and messages are the same.

Here’s my own assessment:

• the likelihood of spillback into an animal somewhere is moderately high if the outbreak continues for a while. Lots of people infected means lots of pets exposed, and transmission to a susceptible species certainly wouldn’t be shocking.
• the likelihood of infection of wild animals is low.
• the likelihood of establishment of monkeypox virus in a wildlife reservoir in currently non-endemic areas is very low.

But, “very low” isn’t zero, and I’ve definitely been wrong before. So, a bit of basic infection control and common sense can go a long way while we’re collecting more information.