As I look back, I can definitely say that one thing that happened in 2010 was that I learned how to spell papillomavirus. I can even pronounce it correctly. And we have a simple acronym--EPV--that is making it much easier for everyone's spelling and pronunciation insecurities.
That's because various strains of the equine virus have been implicated in the lameness problems that I study--in particular, sarcoids and canker. Now, new research from Europe is asking us to consider the role of EPV in reproductive disorders in mares.
The problem of cervical cancer in humans has been considerably reduced in recent years by the development of an efficient and cheap vaccine. Horses also suffer from genital cancer but surprisingly we are only now taking the first steps towards learning what causes the disease.
Work by Sabine Brandt and colleagues at the University of Vienna School of Veterinary Medicine -- together with British pathologist Tim Scase and with Alastair Foote's group from Rossdale's Equine Hospital and Diagnostic Centre in Newmarket -- provides strong evidence that a novel papillomavirus is involved in the equine form of cervical cancer. Their collaboration may pave the way for the development of a cure. The initial results were published in the November 2010 issue of the Equine Veterinary Journal.
Horses are prone to develop genital cancer, especially as they grow older. Male horses are more commonly affected than mares but both sexes suffer from the condition, which is extremely difficult to treat and may result in the animal's death. Because of the similarity of the disease to human genital cancer, it seemed possible that a similar agent might be responsible. Several human genital cancers, including cervical tumours, are known to be caused by a papillomavirus infection, so Brandt and her coworkers used genetic techniques to look for papillomavirus DNA in tissue samples from horses bearing genital squamous cell carcinomas (SCC).
In a statement from the University of Vienna, Brandt conceded that the experiment had the feel of a "magic bullet," although the researchers did have good reasons to suspect the involvement of a virus. Nevertheless, it was extremely satisfying when their hunch proved correct and they succeeded in identifying a novel type of papillomavirus, which they have named Equus caballus papillomavirus-2 (EcPV-2).
EcPV-2 DNA was found in all the genital SCC samples from affected horses in Austria and, independently, in nearly all the samples from such horses in the UK (a single exception may stem from experimental difficulties). The virus has not been detected in any samples from horses without tumours or with other types of cancer.
The scientists have succeeded in isolating and sequencing the entire genome of EcPV-2. Interestingly, the sequence shows that the novel virus is closely related to the two viruses known to be responsible for the majority of genital cancers in humans. This lends further weight to the idea that EcPV-2 might be involved in causing disease in horses.
Taken together, the results provide a strong indication that EcPV-2 causes genital cancer in horses. A final proof would require the demonstration that infecting mucous membranes with the virus eventually leads to the development of cancer and experiments of this kind have -- understandably -- not yet been performed. There is also a need for further studies to examine the frequency of the virus in horse populations. But the initial evidence already seems sufficiently cogent to justify attempts to prepare a vaccine.
Perhaps the work of Brandt and her collaborators may soon lead to the development of preventative measures so that horses -- like humans -- no longer have to suffer from this debilitating and ultimately life-threatening disease.
TO LEARN MORE: T. Scase, S. Brandt, C. Kainzbauer, S. Sykora, S. Bijmholt, K. Hughes, S. Sharpe, A. Foote. Equus caballus papillomavirus-2 (EcPV-2): An infectious cause for equine genital cancer? Equine Veterinary Journal, 2010; 42 (8): 738 DOI: 10.1111/j.2042-3306.2010.00311.x
A Veterinary Microbiology article "EcPV2 DNA in equine squamous cell carcinomas and normal genital and ocular mucosa" by Eva Vanderstraeten, Lies Bogaert, Ignacio G. Bravo and Ann Martens is currently in press.