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Wednesday, September 22, 2021

Cancer research from nature’s bandits

Since March 2010, necropsies have revealed raccoons with a significant similarity. These specimens, studied by the scientists at the UC Davis School of Veterinary Medicine and UC Davis-led California Animal Health and Food Safety Laboratory (CAHFS), all had tumors. Raccoons, with their short lives, are not known for getting tumors so it was rare to find cancer in multiple cases as the cause of death.

Through study of the tumors, researchers discovered a new virus that is believed to be the cause of these tumors. This newly described virus was named raccoon polyomavirus. Polyomaviruses are known to cause cancer under lab conditions, but since cancer usually takes time to form, little is known about their effects in natural environments.

Besides the raccoon polyomavirus virus, Linlin Li, a doctor at the Blood Systems Research Institute, also identified other animal viruses including dog kobuvirus, dog sapovirus, dog bocavirus, dog circovirus, bovine astrovirus and gray fox amdovirus.

These viruses affect many parts of the animal, including multiple parts of the intestinal tract.
“Raccoons have short life spans and generally speaking cancer is a disease more likely with age,” said Patty Pesavento, associate professor of anatomic pathology at UC Davis. “In humans the exposure to polyomavirus precedes cancer by decades. We’re not sure whether this is a transformative event caused by the virus or whether these raccoons are in some way immunocompromised (have weakened immune systems) or exposed to anthropogenic (human-made) pollutants.”

The majority of these raccoons were found in the North Coast and one in Oregon. Eleven so far were found in Northern California, including Marin and Yolo County.

“The tumor types described in these raccoons, which are tumors of the olfactory system, have never been reported in this species,” said Federico Giannitti, a researcher at the UC Davis School of Veterinary Medicine. “We can consider this a new species of emerging disease.”

However, this does not mean that it is restricted to just this area.

“Raccoons are not necropsied unless they are seen with nervous signs (signs of rabies) and there is a chance of human exposure. Necropsy with diagnostic testing is expensive and funding has to be available for disease surveillance in wildlife, which it is not in many states,” said Leslie W. Woods, professor of clinical anatomic pathology at UC Davis. “Some of the raccoons with neurologic disease are sent to veterinary diagnostic labs, and those get a full necropsy, including rabies testing. There may be many more tumors out there, but surveillance is spotty and infrequent.”

There could be other cases that simply were not fully studied due to these reasons, but it is thought that this virus remains in the West Coast.

Of course, concern arises if this is a disease capable of spreading to other species, especially humans, but according to Pesavento, this spread is doubtful.

“[It’s] very difficult to say ‘at all’ when it comes to natural disease. Viruses are very clever,” she said.

Further studies will be needed to see the connection between the virus and the formation of tumors.
Luckily, raccoons are ideal to study in this case since they have short life spans, about 2 to 3 years, which means they can provide a good model for studying the virus. Also, more research will be needed to see if humans had a part in propagating the new virus. Since raccoons exist in habitats very close to us, our actions can easily influence their lives.

These studies could be a great part of our steps toward a better understanding of cancer and how it forms.
“We finally got the complete genome of the [racoon polyomavirus], which was the basis of the following study,” Li said.

KELLY MITCHELL can be reached at science@theaggie.org.

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