A dog has contracted monkey pox from one of its owners, indicating the risk of the virus infecting domestic and wild animals

A dog in Paris has contracted monkeypox from one of its owners, who were both infected with the virus, according to a scientific paper published on Aug. 10, 2022. This is the first case of a dog contracting the monkeypox virus through direct contact with skin lesions on a human.

I am a veterinary pathologist and virologist who has been working with smallpox viruses for over 20 years. I study how these viruses evade the immune system and work on modifying poxviruses to prevent infection and treat other diseases, including cancer.

With the spread of monkeypox in humans around the world, my colleagues and I are beginning to worry about the increased risk of monkeypox spreading from human to animal. If monkeypox spreads to animal species in the US and Europe, the virus could become endemic in these places – where it was absent in the past – resulting in more frequent outbreaks. The report of the infected dog shows that there is a good chance that these fears will become reality.

A microscope image of a bunch of blue circles in a brown-stained cell.
The monkeypox virus — the blue circles in this image of an infected cell — is a smallpox virus similar to smallpox and cowpox and can easily infect many different species.
NIAID/Wikimedia Commons, CC BY

A kind-jumping virus

Monkeypox is a smallpox virus in the same family as variola – the virus that causes smallpox – and cowpox viruses and likely evolved in animals before spreading to humans. Monkeypox causes painful lesions in both humans and animals and can be fatal in rare cases. Researchers have found monkeypox virus in several species of wild rodents, squirrels and primates in Africa, where the virus is endemic. Monkeypox doesn’t need to mutate or evolve at all to infect many different species. It can easily spread from animals to humans and back again.

While quite a bit of research has been done on monkeypox, much more has been done on cowpox, a similar zoonotic smallpox virus endemic to Europe. Over the years, there have been several reports of cowpox infections spreading from animals to humans in Europe.

From people to animals

Until recently, most monkeypox infections occurred in specific areas of Africa, where some animal species act as reservoirs for the virus. These outbreaks are usually contained quickly by isolating the infected and vaccinating people around the infected person. However, the current situation is very different.

With nearly 40,000 cases worldwide as of August 17, 2022 — and more than 12,500 cases in the US alone — monkeypox is now widespread among the human population. The risk of one person transmitting the virus to an animal — especially a wild animal — is small, but the more people infected, the higher the chance. It’s a numbers game.

There are a number of ways viruses can be passed from animals to humans — called spillover — and from humans back to animals — called spillback. Since monkeypox is most easily spread through direct skin-to-skin contact, it is slightly more difficult to transmit between species than COVID-19, but certainly possible.

The case of the dog in Paris provides a clear example of how cuddling or being close to a pet can spread the virus. Previous studies on smallpox viruses such as monkey pox have shown that they can remain active in the stool. This means there is a risk of wild animals, most likely rodents, catching human waste.

A gray rat.
There are a number of species that harbor monkeypox in Africa, such as this Gambian rat. Monkeypox can spread from humans to many other animals, including dogs and probably cats and other types of rodents.
Louisvarley/Wikimedia Commons, CC BY-SA

The monkeypox virus is also present in saliva. While more research needs to be done, it’s possible for an infected person to throw away food that would then be eaten by a rodent.

The chances of any of these events happening are extremely low. But I and other virologists worry that as more people become infected, there’s a greater risk of rodents or other animals coming into contact with urine, feces or saliva contaminated with the virus.

Finally, there is a risk that people will give monkeypox to a pet, who will then pass it on to other animals. A case study in Germany described a cowpox outbreak that was caused when someone took an infected cat to a veterinary clinic and four other cats were subsequently infected. It is possible that an infected pet can somehow spread the virus to wild animals.

How to help

One of the main reasons the World Health Organization was able to eradicate smallpox is that it only infects humans, so there were no animal reservoirs that could reintroduce the virus to human populations.

Monkeypox is zoonotic and already has several animal reservoirs, although these are currently limited to Africa. But if monkeypox gets into wildlife populations in the US, Europe or other locations, there will always be potential for animals to spread it back to humans. With this in mind, there are a number of things people can do to reduce the risks related to animals.

As with any infectious disease, you should be informed about the signs and symptoms of monkeypox and how it is transmitted. If you suspect you have the virus, contact a doctor and isolate yourself from other people.

As a veterinarian, I strongly encourage anyone with monkey pox to protect your pets. The Paris case shows that dogs can become infected through contact with their owners, and it is likely that many other species, including cats, are also susceptible. If you have monkey pox, try to have other people take care of your animals as long as the lesions are present. And if you think your pet has a monkeypox infection, contact a vet so they can test for the lesion and provide care if needed.

Although Monkeypox has been declared a public health emergency, it is unlikely to affect most people directly. Taking precautions can protect you and your pets and will hopefully prevent monkeypox from spreading to the wild in the US as well.

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