Vesicular stomatitis confirmed in California; State Veterinarian’s Office asks Colorado veterinarians to be alert

Vesicular stomatitis confirmed in California; State Veterinarian’s Office asks Colorado veterinarians to be alert

The following message was distributed by the Colorado State Veterinarian’s Office on May 23, 2023.

On May 17, the National Veterinary Services Laboratories in Ames, Iowa, confirmed a finding of vesicular stomatitis New Jersey virus (VSNJV) on an equine premises in San Diego County, California.  One horse, an 11-year-old Quarter Horse mare, on the premises met confirmed vesicular stomatitis virus (VSV) index case definition with compatible clinical signs and virus isolation positive results for VSNJV on swabs from oral lesions.  Additionally, three other equine premises in San Diego County, California, have now met subsequent confirmed case definition with compatible clinical signs and real-time RT-PCR detection for VSNJV.  This is the 2023 VSV index case for the United States and 3 subsequent VSV cases for California.

Known competent vectors for transmission of VSV include black flies, sand flies, and biting midges (Culicoides spp.). The initial epidemiological investigations on all 4 VSV-confirmed positive premises in San Diego County, California, indicate that incursion of VSV-infected insect vectors is the likely source of infection in these herds. Biosecurity measures and vector mitigation on the affected premises have been instituted to reduce within-herd spread of the virus. The animals are being monitored and all VSV-positive premises will remain under state quarantine until 14 days from the onset of lesions in the last affected animal on the premises.

Please see the USDA APHIS Veterinary Services website to read the current situation report.

What Colorado veterinarians need to know

While there have been no cases of VSV in Colorado this year, the cases in California indicate that we could see cases in Colorado during the upcoming insect vector season.

At this time in Colorado, all suspect VSV cases in horses and livestock must be investigated by state or federal animal health officials until Colorado has an index VSV case. The CSU Veterinary Diagnostic Laboratory will not be activated until NVSL has confirmed an index VSV case in Colorado and after activation can only perform equine VSV testing.  CDA VSV Information  

Any vesicular disease of livestock and horses is reportable to the State Veterinarian’s Office in Colorado. Report any cases that have clinical signs suggestive of Vesicular Stomatitis Virus (VSV) immediately by calling 303-869-9130.  If it is after hours, the office voice message will indicate which staff veterinarian is on call.

Veterinarians may also contact the state or federal field veterinarian in your area.

Vesicular stomatitis background

Colorado most recently experienced its largest VSV outbreak in 2019 resulting in nearly 700 quarantines and movement restrictions involving horses and cattle across the state.  The goal in the management of the disease is to accomplish effective control while minimizing the negative economic impacts to livestock owners.

Vesicular stomatitis is a viral disease that primarily affects horses and cattle and rarely in swine, sheep, goats, llamas, and alpacas.  The transmission of VSV is not completely understood, but includes insect vectors such as black flies, sand flies, and biting midges.

The incubation period ranges from 2-8 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.

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.

Tips for livestock and horse owners

  • Strict fly control is an important factor to inhibit the transmission of the disease.
  • Avoid transferring feeding equipment, cleaning tools, or health care equipment from other herds.
  • Colorado fairs, livestock exhibitions, and rodeos may institute new entry requirements based on the extent and severity of the VSV outbreak.
    • If you are participating in an event, please contact the event organizers prior to travel to determine if entry requirements may have changed.
    • A certificate of veterinary inspection (health certificate) issued within 2-5 days prior to an event can be beneficial in reducing risks.
  • If moving livestock interstate, contact the destination state for entry requirements. Each state’s requirements around VSV can be different and subject to change during an outbreak.
  • If moving livestock internationally, contact the USDA APHIS VS Colorado office at 303-231-5385 to determine if there are any movement restrictions or testing requirements for VSV.

Additional resources:
CDA Vesicular Stomatitis Information
USDA APHIS Veterinary Services National VSV Update