With any new, changing or inadequately investigated infectious disease, we need to first understand the scope of the problem, including the range of species that can be infected. The ongoing human monkeypox outbreak has raised concern about spillback of monkeypox virus into animals from humans since, we don’t know much about susceptible animal species.

A recent paper in Eurosurveillance (Shepherd et al. 2022) describes investigation of monkeypox in animals from UK households with one or more persons infected infected with monkeypox.  Affected pet owners were asked if their animals were sick, and if so, that prompted discussion about whether it might be due to monkeypox or another cause, and whether testing for monkeypox was indicated. That’s an easy way to investigate something like this, but it has a few weaknesses:

• Mild disease might be missed by pet owners. While raging pox-like skin lesions would hopefully be noticed, subtle skin lesions, enlarged lymph nodes or some other potential signs of monkeypox wouldn’t likely be detected by the average pet owner.
• Owners might be fearful of the implications of infection in their animal (e.g. quarantine) and therefore not want to disclose potential issues.

Nonetheless, it’s useful to see the results of this study.

154 animals from households with a person with monkeypox were investigated. That included 42 dogs (including one household with 13 dogs), 26 cats (from 14 households), as well as 5 “rabbits or guinea pigs,” one group of 7 unspecified “mammalian livestock,” one group of 64 poultry, and a smattering of tropical frogs, a snake and one “unspecified” animal. We can largely disregard the poultry, reptile and amphibian data, since there’s not much reason to think those species are of any concern with regard to monkeypox infection.  That leaves us with 80 mammals of different species, none of which showed any evidence of overt disease due to suspected monkeypox infection, despite household exposure to the virus. Good news.

The other big thing that is missed using this methodology is assessment of subclinical infections, i.e. where the animal is infected (and maybe infectious) but is not showing any signs of illness. That’s a particular concern for potential reservoir species.

What can we take home from this study?

The big thing this study suggests is that serious infection with monkeypox virus in pets is unlikely. It doesn’t prove it can’t happen, since the numbers are relatively small, but it shows that transmission to pets and subsequent serious disease is probably uncommon, if it occurs at all.  That’s useful information.

It’s still just one step on our path to understanding more about the potential for human-to-animal (and human-to-animal-back-to-human) transmission, as well the range of species that are susceptible to monkeypox.

While there are limitations to this study that are easy to pick apart, the results are still important and useful, and help us think about next steps. To figure out more, we need more intensive studies with veterinary examination and testing of exposed animals, including larger numbers of animals and diverse species. Getting animals examined and tested isn’t a cheap, easy or fast process (we’ve had a really hard time recruiting for our own monkeypox surveillance efforts), so quick basic studies like this can help fill in some preliminary gaps.