This virus isn’t horsing around! A review of the US Vesicular Stomatitis Virus (VSV) outbreak, Canadian export restrictions, and the importance of this reportable disease

By Dr. Dana R Dobbs, Field Veterinarian and Marissa Nelson, Animal Health Technician
Washington State Department of Agriculture (WSDA)

Why are so many horses and some cattle “down in the mouth lately?” Unfortunately, Vesicular Stomatitis Virus (VSV) is hitching a ride north from Mexico with its arthropod vectors during ideal, warm conditions. Vesicular stomatitis is a viral disease that primarily affects horses and cattle. It occasionally affects swine, sheep, goats, llamas, alpacas, and people who handle infected animals. VSV is an RNA virus belonging to the family Rhabdoviridae, genus Vesiculovirus. The two serotypes of particular importance in the United States are VSV New Jersey and VSV Indiana, with VSV New Jersey being confirmed during the current outbreak.

Hopefully, this article will shed some light on the current VSV outbreak, its associated Canadian import restrictions, and the importance of this reportable disease.

2023 Vesicular Stomatitis Virus (VSV) outbreak update

On May 17th, 2023, the National Veterinary Services Laboratory (NVSL) confirmed Vesicular Stomatitis Virus (VSV) in San Diego County, California. Texas soon followed suit with their first case on June 15, 2023. Since the first detection, there have been a total of 119 VSV affected premises identified in California and Texas. Forty of those premises were confirmed positive by NVSL, whereas 79 are suspect. In this current outbreak, 116 equine species, 2 bovine species, and 1 rhinoceros have been clinically affected.

As the outbreak continues to evolve, USDA posts regular situation reports and updates, along with other useful information for veterinarians available at: USDA APHIS | Vesicular Stomatitis (VS)

Thankfully, VSV has not been detected in Washington State; however, there have been issues with horses from affected states trying to enter Canada for special events or exhibitions. Unfortunately, some were turned away at the border when suspicious lesions were discovered.

Canadian export suspension for horses, swine and ruminants in VSV affected states

At this time, export of horses, swine, and ruminants into Canada from VSV infected states is suspended. Exceptions may be granted to those animals moved out of VSV-affected states to reside elsewhere for 21 days. Veterinarians should check with these destination states for any special animal health or testing requirements prior to movement. Additionally, USDA must certify these animals prior to export as follows: “All states in which the animal(s) have resided in the past twenty-one (21) days have been free from clinical and epidemiological evidence of vesicular stomatitis during the twenty-one (21) days immediately prior to export to Canada”.

**It is recommended that US origin animals exporting to Canada and Canadian animals returning home avoid passing through VSV affected states. If this isn’t possible, the Canadian Food Inspection Agency (CFIA) will require further declarations prior to entry and should be contacted well in advance.


Canadian horses, swine, and ruminants in the United States on a Canadian health certificate may return from a VSV affected state within three days of the state being declared affected by the disease. These animals must be inspected by a CFIA Port of Entry veterinarian, or the Canadian health certificate will be invalid.

Traveling to Canada from VSV affected states is still possible for events that have been pre-approved by the Canadian Food Inspection Agency (CFIA). This applies only to horses and ruminants traveling to these competitions and exhibitions, and they must have all requisite documentation. The pre-approved events include:

  • Royal Winter Fair
  • Agribition
  • Calgary Stampede
  • Thunderbirds
  • Spruce Meadows
  • Longines Global Tour
  • Denver Stock Show
  • Houston Livestock Show and Rodeo

To qualify for the exemption, an accredited veterinarian must: 1) Request a CFIA import permit, 2) Use the Veterinary Export Health Certification System (VEHCS) to create a health certificate that includes the addendum statements for VSV and other requirements*, 3) Attach test results for EIA (within 6 months of import) and VSV cELISA results (within 7 days of export), 4) Obtain USDA’s endorsement for the export, 5) Combine all these documents together, and make an appointment for inspection by a CFIA veterinarian. The inspector may ask for the documents to be emailed prior to inspection.

In VEHCS, select “other” as the commodity and PDF upload certificate. Fill out the certificate and line out/initial statement #7. The required addendums will be on the following page and must be signed by the accredited veterinarian and endorsing USDA Veterinary Medical Officer.

Additional information regarding Vesicular Stomatitis Virus?


In the Western Hemisphere, VSV circulates annually between livestock and insect vectors in southern Mexico where the virus is considered endemic. During the warmer months, from late Spring or Summer to late Autumn, arthropod vectors may move north into the United States, favoring areas along waterways. Common arthropod vectors include black flies, sand flies and biting midges. However, other insects such as horseflies and mosquitos, have also been implicated. It is possible that wind currents may play a role in the insects being able to travel over long distances.
The virus also may be spread when moving infected horses to events, by direct contact between horses with lesions, and transfer on contaminated clothing, feed containers, equipment, and other fomites.

Clinical signs

Once exposed, clinical signs typically appear within 2-8 days, and owners initially may notice a slight fever and excessive drooling. Lesions often appear as pale, raised areas or blisters on the lips, nostrils, commissures of the mouth, tongue, oral mucosa, coronary band, prepuce, vulva, and teats. The blisters eventually swell and rupture, causing pain, discomfort, and reluctance to eat or drink. Older lesions may appear as crusted erosions or ulcers. In addition, severe weight loss or lameness may occur, depending on where the lesions are located.

Some common “imposters” of VSV may include course feed, grass awns, wood chips, cribbing, toxins from blister beetle ingestion, other infectious diseases, sunburn, and trauma. If there is any doubt, it is best to play it safe and call the State Veterinarian’s for assistance. A picture is worth a thousand words, and it is very helpful when consulting with the USDA Area Veterinarian in Charge (AVIC) to determine if investigation is warranted and establish its priority.


Vesicular stomatitis is usually short lived and self-limiting, lasting between 7-14 days. Treatment is supportive, and softening grain, hay cubes, and providing anti-inflammatories may be useful. Currently, there is no vaccine approved for use in horses within the United States.

Containing the Virus

Once an animal is diagnosed with vesicular stomatitis, the premises will be placed on quarantine for at least 14 days past onset of lesions in the last affected animal. Other susceptible species on site, such as cattle and swine, will also be placed under quarantine. Horses are not susceptible to Foot and Mouth Disease (FMD), and if VSV is ruled out in a horse and other livestock on site begin to show clinical signs, this testing is especially critical.


Horses with clinical signs should be isolated immediately and strict biosecurity practices put in place. Moving them to a smaller, easier to sanitize area can help eliminate further spread of the virus. It is important to care for healthy animals first, and sick animals last. Having specific clothing and boots for this purpose is ideal. Make sure all feed containers and equipment are cleaned regularly and avoid sharing these items.

Having an insect control program that eliminates or reduces insect breeding areas will slow or stop insects from infecting more hosts. Remove any areas of standing water such as kiddie pools, old tires, and consider housing animals inside with screens and fans. Manure management is also an important tool for keeping insect vectors under control.

Always use personal protective equipment, such as gloves, to avoid human exposure.

General biosecurity guidelines for equids are available at: General Biosecurity Guidelines | AAEP

Vesicular Stomatitis in humans

If owners, farm personnel, or veterinary professionals are exposed to VSV, they may experience influenza like symptoms such as fever, muscle aches, headache, fatigue, and occasional lesions. Most of the time this is rare, but avoiding contact with vesicular fluids, saliva, or nasal secretions and use of gloves or other appropriate personal protective equipment (PPE) is recommended.

Reporting suspicious cases

VSV is a reportable disease at both the state and federal levels. If you suspect an animal may have vesicular stomatitis, immediately contact the State Veterinarian’s office. The disease cannot be diagnosed on clinical signs alone and may resemble other diseases of economic importance. Samples must be submitted to NVSL without delay by a Foreign Animal Disease Diagnostician (FADD). Typical samples include swabs or tissue samples from lesions, fluid from vesicles, and blood for serology. Results are typically available within a few days and there is no charge to the owner.

For further questions or concerns, please contact the WSDA State Veterinarian’s office at 360-902-1878, or for more detailed information, including VSV fact sheets, visit USDA’s website at: USDA APHIS | Vesicular Stomatitis (VS)