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When I first saw headlines going around about a canine cancer that’s passed through sniffing one another’s private parts, I was alarmed. My dogs, like all dogs, love sniffing other dogs in the most intimate of ways.

Why haven’t I heard of this before? Have you?

As it turns out, it’s not common where I live in the United States, nor is it particularly deadly. While it’s not something we need to panic about, it’s always good to know the facts when it comes to protecting our dogs.

Contagious Dog Cancer – What Is It, Exactly?

Cancer is not contagious. Usually.

You might have heard of human papillomavirus (HPV) a virus in humans that’s passed through sexual contact. It’s the one that’s prevented with the Gardisil vaccine.

HPV in humans usually clears without symptoms, but in some people it causes bouts of genital warts, and in rare cases the virus causes cells to mutate, leading to cervical, throat, vulvar, and penile cancers. But the virus itself does not cause cancer, it just increases the risk of developing cancer later on.

Canine transmissible venereal tumor (CTVT) in dogs is not caused by a virus. Instead, the actual cancer cells act like a virus, transmitting at points of contact.

Dogs most often get CTVT on their genitals through mating. It’s less likely, but possible, to affect their nose, mouth, or face through licking or sniffing.

Since it’s not caused by a virus, a vaccine does not exist to prevent it. Also interesting to note: as far as I know, there are no similar cancers in humans.

Is CTVT in Dogs Common?

CTVT is common in parts of the world where dogs run free, mate, and interact with little human intervention. Rural areas, places with street dogs, countries with low spay and neuter rates all tend to have high rates of CTVT.

But CTVT is uncommon in the United States and Canada, and other places where most dogs are spayed or neutered and not allowed to roam.

How Can I Protect My Dog From CTVT?

Unless you live in an area where it’s common, you probably don’t have to worry.

Keeping your dog inside, having a fenced-in backyard or keeping your dog on a leash, and preventing them from roaming is smart, not only to reduce the risk of transmissible infections with any stray dogs in your area, but also to keep your dog safe from getting hit by a car, stolen, or lost.

If you visit a dog park regularly, you probably don’t have to worry about your dog sniffing their friends and other frisky behaviors. Unless your dog’s friends are allowed to roam in rural areas, they most likely are not carriers of CTVT.

If your dog is not already spayed or neutered, it might be a good idea to get them fixed. There’s a ton of debate on the best age to do it, and the pros and cons, but reducing their drive to roam for a mate, plus keeping them safe from infections of the reproductive tract are two big pros.

CTVT has risen in the United Kingdom in the past few years, and researchers suspect it’s because more people are adopting their dogs from other countries.

Where Is CTVT Most Prevalant?

If you travel abroad with your dog, yes, you might need to worry about protecting them from CTVT. In the chart below, you can see where the cancer is most prevalent.

CTVT is endemic in 90 countries and it’s seen in more than one percent in the canine population in 30 of them.

If you live in or travel to a region where CTVT is prevalent, take extra care to keep your dog from interacting with free-roaming dogs.

Chart from University of Cambridge Department of Veterinary Medicine / Andrea Strakova

Are Male Dogs More Likely To Develop CTVT?

A lot of the current headlines are saying that male dogs are four times as likely to develop CTVT. This is might be misleading.

Male and female dogs are equally likely to develop CTVT.

The cancer usually affects the genitals, though it causes oral and nasal tumors in a small percentage of cases.

Male dogs tend to lick and sniff other dogs’ genitals more than females do. So, they are four times more likely to develop CTVT, but as a whole, they’re only as likely to develop CTVT genital tumors as females.

Symptoms of CTVT

For male and female dogs with CTVT, early signs usually include licking or chewing at the genitals. The skin may become thickened or otherwise unusual in appearance. There may be swelling, bumpy, textured tumors that may bleed.

How Does CTVT Affect Dogs?

Dogs with CTVT have living cancer cells on their external genitalia that can transplant onto another dog’s body through close contact.

It’s unclear if CTVT is only contagious if the dog has visible tumors or lesions on their genitals. Of course, dogs are curious, so they may even be more likely to investigate a dog with cancerous lesions.

Some good news: Just 0-5% of cases metastasize to other parts of the body.

CTVT responds well to chemotherapy. Almost all cases are treatable, and the cancer generally does not spread.

Lindsay Pevny
Lindsay Pevny lives to help pet parents make the very best choices for their pets by providing actionable, science-based training and care tips and insightful pet product reviews.

She also uses her pet copywriting business to make sure the best pet products and services get found online through catchy copy and fun, informative blog posts. She also provides product description writing services for ecommerce companies.

As a dog mom to Matilda and Cow, she spends most of her days taking long walks and practicing new tricks, and most nights trying to make the best of a very modest portion of her bed.

You'll also find her baking bread and making homemade pizza, laughing, painting and shopping.