When my wife and I had our second baby last summer, I took a few weeks to help adjust to our growing family. With my 9-5 on hold and a newborn boy in the house, any semblance of a schedule was out the window.

My wife and I queued up a few TV shows we had been too busy to watch and, after the oldest went to sleep each evening, binged on them deep into the night while our newest family member slept intermittently on our laps.  

At about 3 a.m. on one of those late nights, our cat started meowing sternly near the door to our backyard. I went to examine the scene and found a raccoon staring directly back at the cat, calmly and patiently. After about 20 seconds, the raccoon cruised through the backyard and up a large oak tree — out of sight.

I wondered: Were raccoons standing nose-to-nose with my cat routinely in the middle of the night, or had I just witnesses something rare? I had not seen a single raccoon near the house during the previous two years I lived there.

Fortunately, because my job is at the UC Davis One Health Institute, I had an interview scheduled with Professor Patty Pesavento a few weeks after returning to work. I was about to get educated on raccoons.

Serious tumors in raccoon’s nasal cavities

Pesavento is a pathologist at the School of Veterinary Medicine, where she has spent years studying a disease called raccoon polyomavirus, which causes serious tumors in raccoons’ nasal cavities. These generate intense pressure on the brain, resulting in zombie-like behavior and, ultimately, death.

If you were to have asked Pesavento 10 years ago whether cancer was a major concern in wildlife, her answer would have been a flat “no.” But her work with raccoons in recent years has changed that.

To understand what might be happening in these foragers, it’s worth looking at how their environment has changed over time.

Since Levittown, more food waste encourages raccoons

The first planned suburb was Levittown, New York, in 1947, and similar housing developments swept the nation shortly thereafter. Raccoons, which had previously either lived amid the hazards of the city or scraped by on what they could forage in the forest, suddenly had saw their environment transformed by much expanded territory for foraging and abundant human food waste left out for the pickings.

As raccoons wander nightly in suburbia, they repeatedly engage with the products (and germs) of humans, domestic animals and other urban wildlife. Each interaction with a cat bowl or a discarded piece of food represents the potential to share viruses with humans and their pets. 

In many suburban neighborhoods, on a city block raccons match people in population. Not only are they nocturnal, but also they are incredibly smart: Tracking cameras have demonstrated that raccoons often follow nightly routines, built largely around avoiding human schedules. That’s why my own sightings began only when I deviated from my usual schedule with my newborn.

Raccoons with tumors wander during the day

The raccoons that end up in Pesavento’s lab are typically found wandering among people during the day, severely affected by the tumors that have filled their nasal cavities, as you can see in this video. The virus in the tumors, raccoon polyomavirus, is in a family of viruses related to human papillomavirus (HPV), which can cause cervical cancer in women. 

“When we get a raccoon with a tumor, we’re usually months or even a year beyond when they were first exposed to the virus,” says Pesavento. “How it gets into their brains, we have no idea.”

But Pesavento and her collaborators remain on the case. The team has proven a link between raccoon polyomavirus and the tumors, so the next step is to understand as much as they can about the polyomavirus itself. How does it spread from one animal to another? How and when is it shed? How does it live in those cells without being detected by an animal’s inflammatory system?

You can learn more about Pesavento’s raccoon polyomavirus work on the School of Veterinary Medicine’s website. This blog post is adapted from a story in the One Health Institute’s online magazine, Evotis. Subscribe here.

Justin Cox is content marketing manager for the UC Davis One Health Institute and the Karen C. Drayer Wildlife Health Center.