Papillomavirus suspected in formation of equine genital tumors

Equine genital cancer, the second-leading cause of cancer in horses, may be triggered by a newly identified papillomavirus, known as EcPV-2.

Europe-based researchers say the virus may be instrumental in the development of equine genital epithelial tumors.

Help on the horizon: New research shows that equine squamous cell carcinoma may be a virus-induced tumor and that someday a vaccine to prevent the offending virus, papillomavirus, may help prevent this form of cancer.

"Based on our current knowledge, it seems very likely that equine squamous cell carcinoma (SCC) is a virus-induced tumor. However, further investigations are warranted to fully confirm this suspected association of EcPV-2 with SCC," says Sabine Brandt, DVM, one of the study's collaborators, based at the University of Veterinary Medicine in Vienna, Austria.

The research and its implications

Investigators—led by study author Tim Scase, BSc, BVM&S, PhD, MRCVS, Dipl. ACVP, a veterinary pathologist and director of Bridge Pathology Ltd., a diagnostic immunohistochemistry laboratory in the United Kingdom—examined tissue samples from genital tumors in male and female horses. Horses involved in the study came from Australia, the United Kingdom and Austria. The work culminated in the study, "Equus caballus papillomavirus-2 (EcPV-2): an infectious cause for equine genital cancer?" which was published in the November 2010 Equine Veterinary Journal.

In the study, EcPV-2 was detected in the majority of cancerous tissue samples assessed; conversely, it was not found in any healthy tissue samples. This came as a surprise to the research team.

"We almost never found EcPV-2 in healthy horses (in the meantime we tested almost 100 healthy animals) and only rarely found the virus in ocular SCC—the few positive ocular lesions were metastases," Brandt says. This is in contrast to a previous study cited by Brandt (Vandenstraeten et al., 2010, Veterinary Microbiology) that found EcPV-2 in half of the samples taken from unaffected horses, a finding that she says needs to be addressed.

The findings may lead to a new generation of a vaccine to prevent the disease in horses, according to the researchers. Creation of a vaccine would parallel work being done on the human side, where vaccinating against tumor-causing papillomavirus species is a preventive measure under way to address cervical cancer.

In the meantime, Brandt says early diagnosis by veterinarians is important for successful treatment of horses. "The smaller the lesion, the earlier its stage, the better the prognosis. Small, precancerous lesions contain smaller amounts of viruses, and their treatment is less painful, time- and cost-intensive," she says.

When treating horses, Brandt says that veterinarians may consider the option of antivirals as adjuvant therapy to reduce the risk of tumor recurrence after excision. Routinely cleaning the horses' external genitalia is a disease-prevention measure and helps disclose lesions during veterinary examination. When addressing acute genital SCC, she says to keep the horse in a living space separate from other horses to prevent the spread of virus.

Linking associations

In the wake of the study findings, the next goal, Brandt says, is to establish a pathological association between the virus and disease.

"This means that we will particularly study the physical state of the virus, try to isolate viral particles, conduct infection studies in equine epithelial cells in vitro and investigate the effect of viral infection on these cells—whether the virus transforms these cells (makes tumor cells out of them)," she says.

Further, researchers may also pursue development of new prophylactic and therapeutic approaches if EcPV-2 is found to be liable for SCC-type cell transformation, according to Brandt, who declined to elaborate on any specifics for the new approaches.

Skernivitz is a freelance writer in Cleveland, Ohio.