A U.K. veterinarian has possibly linked common face flies to the spread of sarcoids, one of the most commonly encountered equine neoplasias (tumors), and it is conceivable that the risk of spreading sarcoids could be minimized through horse management techniques. The research also further supports that bovine papillomaviruses (BPV) are involved in causing equine sarcoids in horses.

Jeremy Kemp-Symonds, MRCVS, a PhD student at the Animal Health Trust in Newmarket presented study results during the clinical research sessions at the 46th Congress of the British Equine Veterinary Association, held in Edinburgh, Scotland, Sept. 12-15, 2007.

"Despite being very common, there's a great deal that we don't understand about equine sarcoid," said Kemp-Symonds. "It appears to have a viral etiology, but an unresolved mode of transmission." He noted that fly vectors are mentioned often in the scientific literature about sarcoids, and he said there are numerous anecdotal reports of sarcoids developing at sites of previous injury and trauma. He also said it is common for horses to get sarcoids in the perigenital region, where flies often sit.

According to Kemp-Symonds, Musca autumnalis face flies feed on lachrymal (tearduct), oral, and nasal discharges, and wound secretions. "M. autumnalis is closely associated with predilection sites for sarcoids, and it's an important vector of veterinary diseases," he added. The researchers collected and froze more than 500 M. autumnalis flies infesting six sarcoid-affected Thoroughbred or Thoroughbred-cross horses from the Wye Valley area (encompassing the border of England and Wales). They ran a type of DNA assay called a polymerase chain reaction test on the flies and on tissue from sarcoid-infected horses.

"Ninety-eight percent were coming back positive for BPV-1 and BPV-2 (bovine papillomaviruses)," he said. These papillomaviruses are commonly accepted to be the causative agent of the equine sarcoid. "When we looked at the tissue samples, we got no amplification from any of the control tissue (tissue without sarcoids)." The BPV types were very similar, which is suggested of locally active subtypes of BPV.

These results also suggest that M. autumnalis could be a mechanical vector of both BPV-1 and BPV-2.

Additionally, if the potential exists for sarcoids to be spread through wounds, he suggested there might be "some iatrogenic involvement in these cases," meaning that sarcoids could be induced inadvertently by a veterinarian or by medical treatment or diagnostic procedures. 

"You can try and minimize fly infestations, especially animals with open wounds, and post-surgical cases," he said. Control measures include equine housing, insecticides, repellents, and traps.

"My suspicion is there is horse-to-horse transmission," he said. "These horses were geographically very isolated from horses where there were cattle with BPV. When you look at the habits of flies, they tend not to fly great distances to go from one meal to another. About 3 km is as far as they go. So it's easy to fly from a sarcoid-infected horse to a horse with open wounds.

"Any fly potentially could do it," he concluded.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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