Post Reply - Pets & Pandemics

Information on human-to-pet mpox transmission is still very limited. Two potentially infected animals were reported during the global outbreak in 2022 – a dog in France and a puppy in Brazil. However, there was some debate about whether positive results were from true infection or just contamination of the pet’s skin with viral bits from the infected humans in the same households.

Fortunately, we now have some new information from the US. An ahead-of-print article in Emerging Infectious Diseases (Morgan et al. 2024), describes an investigation in the US between July 2022 and March 2023. They collected skin swabs and blood samples from pets of people with mpox from 21 households. They sampled 24 dogs, 9 cats and 1 rabbit, obtaining a total of 191 swabs from animals and 56 swabs from the animals’ environments (e.g. beds, bedding, toys, bowls). The results were interesting:

• MPXV DNA was identified by PCR from five animals (4 dogs, 1 cat) from 4 households. Two positive dogs were from the same household. That’s an overall positivity rate of 17% in dogs and 11% in cats sampled.
• Multiple positive results were obtained from all of the positive animals. Overall, 12% (22/191) of animal samples were positive.

Breaking it down by body site, positives were from:

• 29% (4/14) of skin lesion samples
• 16% (6/37) of ventral skin/fur (stomach) samples
• 12% (4/33) of dorsal fur (back) samples
• 11% (4/35) of periocular (around the eyes) samples
• 8% (3/36) of anorectal (butt) samples
• 3% (1/36) of oral samples

Researchers also tested for RNase-P as an indicator of human DNA contamination, and all PCR-positive samples were also positive for RNase-P. While that doesn’t mean that the MPXV DNA all came from direct human contamination, it means there was evidence of human contact with the same sites at the same time.

Seven animals had skin lesions, but five of those had skin lesions before the owner got sick, so those cases were likely unrelated. Two pets developed skin lesions after the owner got sick (or at least no one noticed them before that) and both were PCR-negative for MPXV.

Twenty-nine percent (29%) of households had positive animal-associated environmental samples (e.g. dog beds, toys, bowls). All households with positive animals had positive environmental sites, but so did two households without positive animals. Environmental samples are always hard to assess in situations like this, because a positive result could be from contamination from the person or the pet. Environmental samples also don’t tell us risk, since PCR testing will also detect dead virus. It’s more of an indicator of the viral load in the area, and provides some suggestions of contamination routes and what sites might potentially be of concern.

PCR is a really sensitive testing method that can pick up even small bits of dead virus, so the researchers also followed up with viral culture, which is more time consuming, specialized and hazardous, while also being less sensitive – which is why it’s not typically uses it for initial testing. Culture is useful for figuring out if there truly was an active infection, because it only detects live virus. All PCR-positive samples in this study were negative on culture. That’s a bit hard to interpret with confidence.

• It could mean that infection levels were low, since culture isn’t sensitive.
• If sampling was done late in infection (which would be common in studies like this, since researchers can’t usually get into households really quickly, then active infection may have waned by the time of sampling.
• It could be that samples didn’t pick up much virus.
• It could also mean that PCR-positives were from contamination with dead virus.

Testing for MPXV antibodies in the blood was also performed in 20 dogs at the time of the first site visit, and all were negative. More importantly, 22 dogs were tested 3-4 months later and still had no detectable antibodies. That’s more important because initial negative results might just be because the body hadn’t yet produced detectable antibodies to the virus, but by 3-4 months, antibodies should be present if the animal was previously infected. It’s not a complete guarantee that the dogs weren’t infected, since we don’t know how good the antibody test is or how robust antibody production might be if infection was mild and transient. However, it provides more evidence that PCR-positive results could be due to contamination or a very low (and maybe irrelevant) level of transient infection.

Does this mean dogs and cats can or cannot be infected with MPXV by infected owners?

What this shows is that pets are definitely being exposed from their owners (not surprising) and that it’s possible that some are getting infected. However, it’s unclear whether these were true infections, and even if they were true infections, the low viral load and lack of clear mpox lesions would suggest that the transmission risk posed by pets is probably very low to negligible.