Fly control is vital to prevent VSV |

Fly control is vital to prevent VSV

After an initial confirmed case in Weld County, the Vesicular Stomatitis quarantines now include 15 premises in Weld, Larimer and La Plata counties. Colorado is the third state with confirmed cases of the virus, behind Texas and New Mexico.

Horses on eight separate premises in Weld County are currently under quarantine, in addition to a quarantine on five properties in Larimer County, and two in La Plata County after the National Veterinary Services Laboratory first reported positive results on July 3. The initial Colorado disease investigation was completed by a field veterinarian from the State Veterinarian’s Office at the Colorado Department of Agriculture.

Colorado State Veterinarian Dr. Keith Roehr said the virus causes oral blisters and sores that can be painful, causing difficulty in eating and drinking.

According to the Department of Agriculture, the Weld County epidemiological investigation indicates an incursion of VSV-infected insect vectors is the likely source of infection.

Biosecurity measures and vector mitigation have been instituted on both locations to reduce the potential spread of the virus. The animals are being monitored daily and the index premises will remain under state quarantine until at least 14 days from the onset of lesions in the last affected animal on the premises. There are no USDA approved vaccines for VSV.

According to a press release issued by the Department of Agriculture, vesicular stomatitis is a viral disease that primarily affects horses and cattle, and occasionally swine, sheep, goats, llamas and alpacas. The transmission process of VSV is not completely understood, but includes insect vectors such as black flies, sand flies and biting midges.

The incubation period ranges from two to eight days. Clinical signs include vesicles, erosions and sloughing of the skin on the muzzle, tongue, teats and coronary bands. Often excessive salivation is the first sign of disease, along with a reluctance to eat or drink. Lameness and weight loss may follow.

Roehr said fly control is vital in preventing exposure to VSV.

“Good fly control centers mostly around manure management and doing other things like removing suitable fly reproduction habitat from moist areas, feed or hay that’s wet and doesn’t dry out,” he said. “It’s a little different than mosquitos, it’s not standing water necessarily but flies like moist environments and manure to increase in numbers.”

Using fly sprays on individual horses help protect the horse but he said they do little to reduce the fly population and must be applied frequently.

Organizers of equine events, he said, may elect to either require the standard certificate of veterinary inspection for intrastate travel but others may require that a veterinarian examine the horse three to five days prior to arrival at the event, issuing a timed certificate of veterinary inspection.

“What that does is allows the veterinarian to do a thorough examination of the mouth, tongue, and coronary band around the hoof and check to see that the horse doesn’t have clinical signs,” he said.

The design of this is to allow horses with a certificate of veterinary inspection written in the short time period prior to an event, owners could be waved into the event to stall, without an on-site inspection. Without the timed certificate of veterinary inspection, it is Roehr’s recommendation that the equine event have a licensed veterinarian on site to oversee the process of mouthing horses arriving. The logistics, he said, is difficult at an event with a high number of horses.

There is no treatment for the virus itself but horse owners can provide supportive care, based on the level at which the horse is affected.

Humans may become infected when handling affected animals, but this is a rare event. To avoid human exposure, individuals should use personal protective measures when handling affected animals. ❖

— Gabel is an assistant editor and reporter for The Fence Post. She can be reached at or (970) 392-4410.

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