I got a lot of media questions about hantavirus after the recent cluster of human cases was identified associated with a cruise ship, but those questions were primarily focused on basic facts about virus itself and its general epidemiology. As things have dragged on, there are now more questions about hantavirus and companion animals – not because there are any major issues with pets and this virus, but more likely just because people are getting bored with the usual talking points and are looking for other content.

That said, there are some interesting aspects to consider when it comes to hantavirus and dogs and cats. Pets can be exposed to hantavirus just like people, through contact with reservoir species (i.e. rodents), or their feces, urine or saliva. Cats and dogs are technically at higher risk of exposure in many ways, since they are more likely to have close contact with rodents and to be sniffing around contaminated areas.

I want to start with the key point that the issues with hantavirus in pets are near negligible. I’m going to talk about some areas we should think about with emerging or unusual disease events out of an abundance of caution, not because there’s a major concern with this specific event. So please don’t freak out. Finding that sweet spot between awareness and panic is tough with infectious diseases.

This post will focus on issues to consider specific to the cruise ship cluster. I’ll try to cover some of the more general considerations with hantavirus and pets in another post.

Key point: Despite evidence of human-to-human transmission of this particular hantavirus strain (Andes virus) on the ship, such transmission is still rare. If human-to-human transmission is rare, human-to-pet transmission should be at least as rare, if not even rarer.

Issues with pets and emerging diseases in general revolve around three main concerns:

1. Pets getting sick (concern for pet health and potential for them to be sources of infection)
2. Pets getting infected but not sick (no concern for pet health, but bigger to other animals and people to have infectious but apparently healthy animals around us)
3. Pets acting as vectors of a pathogen whereby they are not infected but can move the virus from place to place (e.g. virus contamination of their haircoats)

We don’t know that any of these are an issue, and they are probably of no concern with this cluster. Infections in dogs and cats are already very rare, and even if infected, the transmission risk from a pet would be very low. But this is also an opportunity to take some basic and practical prevention measures when the risk isn’t well known.

I haven’t seen any reports of dogs being on the ship (e.g. service animals). That removes the highest risk situation with regard to transmission. That leaves us with pets owned by people who have left the ship. Those who have been released from the cruise ship are being monitored, and in some situations tested. Different countries are taking different approaches, but it seems like voluntary quarantine is being used in many places. That focuses primarily on keeping potentially exposed people away from other people. The question I always have with household quarantine is “what about the pets?” This question seems pretty simple, and has come up in the context of various diseases, but rarely do we get an answer.

• If someone is quarantining in a household, we need to know if they have pets, and if there is a risk to/from the pet for the disease in question. If there is, or if we can’t say there’s no risk, we should treat the animal like a person, i.e. try to keep the quarantined person away from the pet as well. That helps ensure they don’t infect or contaminate the animal, both for the animal’s health and to avoid the risk the pet might then pose to other animals or people.

With other infectious diseases (not likely applicable here), there can also be concerns about the animal acting as a mechanical vector that can lead to indirect transmission, similar to a contaminated surface or object. As I’m writing this, Alice (my cat) is perched next to me. If I have a respiratory virus and touch my face, and then her, I may contaminate her haircoat. If she then visits someone else in the house they pet her a short time later, that could transfer virus to them, even though Alice wasn’t infected. The worst case scenario is I contaminate or infect Alice, and then she goes outside and infects another animal. Then maybe I’ve released the virus into the broader community, or the wildlife population. This was something we were trying to get across when voluntary isolation was used when SARS-CoV-1 emerged in the early 2000s, and then again with SARS-CoV-2 during the COVID-19 pandemic (rarely with any success).

Again, the issues with this hantavirus cluster specifically are very limited and there’s probably no concern:

• The odds of a person that is quarantining being infected are really low.
• The odds of an infected person infecting an animal are even lower.
• The odds of a person being infected, infecting their animal and that animal getting sick or transmitting the virus to someone else approach zero.

So, why are we even talking about it? Good question. We probably know enough about Andes virus to just say “don’t worry.” However, our knowledge of the potential role of pets in a lot of diseases is pretty low, and we can take simple steps to reduce that risk.

My emphasis here is we should default to assuming there could be cross-species transmission issues and apply basic control measures accordingly, unless/until we determine that there’s no need, rather than waiting until we see a problem and then reacting. With Andes virus, a rapid risk assessment could be done to determine the likely risk and the relative certainty of risk, to determine whether or not it is necessary to tell people to isolate from animals too. Despite all our past experiences and recognition of the scope of susceptible species for many emerging diseases, we are still reactionary when it comes to risks to and from animals.

• Do I want people to worry about their pets if they’ve been exposed? No.
• Do I want exposed persons to isolate from their pets? Maybe. If they are isolating from people, it makes sense to isolate from their pets. However, if that’s not practical or if the pet is the person’s key emotional support through quarantine, I’d have them quarantine together.
• Do I want people to fear animals that might have been in contact with an exposed person? No. We’ve seen over-reactions like this in the past.

The issues with hantavirus and most pets are near negligible, but it’s another reminder that the difference between “humans” and “animals” is in our brains. To a virus, we are all just animals of different species, and we all have the potential to be a nice susceptible host.