Vesicular Stomatitis (VS) Outbreak Updates

Flies on horse's face carriers of vesicular stomatitis.
Flies on horse's face carriers of vesicular stomatitis. Carien Schippers

Newsdate: Thursday, September 28, 2023 – 11:30 am
Location: LEXINGTON, Kentucky

With the outbreak of VS in California, Dr. Katie Flynn, Senior Staff Veterinarian-Equine Health & Biosecurity, saw a specific need to have a learning module focused on recognizing VS symptoms. This is intended to safeguard horse health and the continuous operation of competitions.

Vesicular stomatitis virus clinical signs on horse's lips, tongue and nose.

Vesicular stomatitis virus clinical signs on horse's lips, tongue and nose.

Vesicular stomatitis is a viral disease of horses and other animals and the infection results in blisters, crusts, and ulceration of the lips, muzzle, nose, tongue, ears, sheath, teats, and/or coronary band.
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The module is available to anyone interested in learning more about VS and obtaining insights into identifying suspect lesions on horses.
This module will provide the following:
    •    An overview of the vesicular stomatitis virus
    •    An outline of requirements for USEF-licensed competitions with horses from VS-affected area(s)
    •    An explanation of the USEF competition arrival examination protocols
    •    Picture examples of VS lesions
    •    An outline of the role of a technician and veterinarian for identifying and rejecting VS-suspect horses
Eligibility for appointment as a “designated individual” under the VS policy can be attained by completing the module and a quiz.

California- Riverside (9/7), San Luis Obispo (9/5), Santa Barbara (9/24), Ventura (9/11)NOTE: Counties are removed from this list 30 days after the last premsises in the county has been released from quarantine. The date in parenthesis is the date of quarantine release for the last VS quarantined premises in that county. Counties with no dates listed have at least one premises remaining under quarantine .

For the complete USDA Vesicular Stomatitis Situation Report Last Modified: Sep 22, 2023: visit

Vesicular stomatitis (VS) is a viral disease of horses and other animals. Infection results in vesicles (blisters), crusts, and ulceration of the lips, muzzle, nose, tongue, ears, sheath, teats, and/or coronary band. Transmission is predominantly by black flies, sand flies, and biting midges. The virus is in the active lesion, thus animals with active lesions can transmit the virus by direct contact, shared feed/water sources, and other carriers contaminated by infective lesions, vesicular fluid, and/or saliva. The lesions are self-limiting and typically resolve within 14 days. Humans can be infected from exposure to this virus and have mild flu-like symptoms.
USEF supports continuing competitions in VS Affected States and competitions which include horses from VS Affected States provided the biosecurity measures listed below are implemented.
As we have learned over the last few years, we live in a world of equine infectious disease events which are outside of our control. Thus, we must make adjustments to best support competitions while protecting our equine athletes through the implementation of necessary biosecurity measures.

Critical Control Measures For ALL USEF licensed Competitions– Reporting of Vesicular Lesions
    •    All competitions to institute immediate mandatory reporting of horses with vesicular lesions to competition management.
    •    All competitions to require immediate isolation of horses with vesicular lesions or temperatures over 101.5°F.
    •    All competitions to immediately report any horses with vesicular lesions to State Veterinarian’s office in the state in which the event is held AND to the USEF Equine Health and Biosecurity Veterinarian Dr. Katie Flynn ( or 859-225-6991)
Changes in USEF Vesicular Stomatitis Requirements Effective September 1, 2023

U.S. Equestrian continues to work with state and federal animal health officials as well as subject matter experts on the Vesicular Stomatitis outbreak in California.

Based on these discussions with experts, the current case data, the slowing of virus spread in California and the successful implementation of control measures at equine events, the USEF is making the changes to the protocols.

It is important competitors and competition staff continue to monitor the health of our equine athletes on the competition grounds. Failure to quickly identify lesioned horses and the resultant spread of the virus on the events grounds poses great risks to the future of our events. Ultimately, failure to take these biosecurity measures could lead to the cancellation of USEF competitions.

See complete article with all Vesicular Stomatitis Requirements .

Press release by US Equestrian

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