Sarcoid-Causing Virus Harbored by Circulating Blood Cells

Aggressive research efforts to discover how the sarcoid-causing bovine papillomaviruses (BPV) are spread either within or between horses have resulted in the identification of BPV genetic material (DNA) in circulating blood cells. This novel finding suggests a possible mechanism by which horses prone to developing sarcoids become latently (invisibly) infected and potentially contribute to the spread of the virus.

Sarcoids are a common form of skin tumor in horses. While non-malignant, these growths can be problematic because they can spread to virtually any location on the body and can compromise the use and welfare of the horse. To date, there is no known cure and the mode of BPV transmission remains undetermined.

Until now, BPV DNA has not been detected in horses circulating blood cells (peripheral blood mononuclear cells--a particular kind of white blood cell). Because DNA from other type of pappillomaviruses has been identified in blood, the study authors re-visited this issue and chose to look for very small amounts of DNA.

The authors developed a highly sensitive polymerase chain reaction (PCR) test capable of detecting very small amounts of BPV DNA in the blood from sarcoid-infected horses. Blood from 66 horses was subsequently tested using this new PCR test.

The PCR test correctly identified the three sarcoid-infected horses, and was negative in the remaining 63 sarcoid-free horses. These results suggest that BPV lies latent in circulating blood cells in infected horses and is a reservoir for infection.

While this mechanism is not likely involved in the spread of infection between horses, it might explain how the virus can be spread in utero from infected mares to their foals and how multiple sarcoids can develop in individual horses.

Further research to further explore the biological and pathological significance of this discovery is ongoing.

The study, "Peripheral blood mononuclear cells represent a reservoir of bovine papillomavirus DNA in sarcoid-affected equines," was published in the June 2008 edition of the Journal of General Virology.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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