UC DAVIS (US) — Rare brain tumors found in raccoons may be linked to a previously unidentified virus and the findings could lead to a better understanding of how viruses cause cancer in people and other animals.
Necropsies conducted since March 2010 found brain tumors in 10 raccoons from Northern California and Oregon. The common factor, found in all of the tumors, was a newly described virus, dubbed raccoon polyomavirus.
Researchers suspect this virus contributes to tumor formation. Two more raccoons with the tumor and the virus were found in Yolo and Marin counties in California since September 2012, when the article was submitted for publication.
Polyomaviruses, which are prevalent but rarely cause cancer, do not typically cross from one species to another, so the outbreak is not expected to spread to people or other animals.
“Raccoons hardly ever get tumors,” says study author Patricia Pesavento, a pathologist with the School of Veterinary Medicine at the University of California, Davis and author of the study published in the the journal Emerging Infectious Diseases. “That’s why we take notice when we get three tumors, much less 12.”
Polyomaviruses are known to cause cancer under laboratory conditions. Less is known about their ability to cause cancer under natural conditions among people, because cancer often takes decades to develop.
Raccoons, with their short lifespans of two to three years, can provide a model for studying how these viruses spread outside the laboratory, how they cause cancer, and how easily they can jump from species to species.
Of the 12 raccoons affected, 10 were collected from Marin County. Pesavento said this does not mean the virus is limited to that county, or even to Northern California. Marin County is home to WildCare, an animal rescue and rehabilitation center that routinely submits animal remains for diagnostic testing, which might result in a sampling bias.
Other California raccoons were submitted by Lindsay Wildlife Museum in Contra Costa County and Sonoma Wildlife Rescue. Pesavento’s lab is collecting specimens and data from other sources across the country, looking for the virus and for raccoon exposure to it.
More research is needed to understand whether an environmental toxin, genetics, or other explanation is contributing to the cancer. The study shows that raccoons are exposed daily to human waste, garbage, environmental toxins and environmental pathogens, as they travel along sewer and water lines.
“This is just the beginning of a story,” says Pesavento, adding that high rates of cancer among wildlife are found in animals that live in close proximity to humans. “Wildlife live in our fields, our trash cans, our sewer lines, and that’s where we dump things. Humans need to be guardians of the wildlife-human interface, and raccoons are important sentinel animals. They really are exquisitely exposed to our waste. We may be contributing to their susceptibility in ways we haven’t discovered.”
Infectious pathogens, such as viruses, are associated with 15-20 percent of all human cancers worldwide, according to the American Cancer Society. For example, human papillomavirus can lead to cervical cancer. Feline leukemia virus, for which UC Davis developed a vaccine, can cause cancer in cats. UC Davis also continues to study Marek’s disease, a deadly virus in chickens that is providing insight into human cancer.
“This work to investigate natural associations of cancer verifies the importance of our One Health approach to addressing complex biomedical problems, such as viral causes of cancer,” says Michael Lairmore, dean of the School of Veterinary Medicine, of which the UC Davis One Health Institute is a part.
“Understanding how infectious agents may contribute to cancer in animals has provided fundamental new knowledge on the cause of cancer in people.”
Researchers from University of California, San Francisco, Blood Systems Research Institute in San Francisco, and Louisiana State University in New Orleans contributed to the study that was funded through The Bernice Barbour Foundation, the UC Davis Center for Companion Animal Health, and Meadowview Foundation.
Source: UC Davis