Other Names
- Vesicular stomatitis virus (VSV) infection
- Vesicular stomatitis (VS)
What is Vesicular Stomatitis in Horses?
Equine vesicular stomatitis (VS) is a viral disease caused by the Vesicular Stomatitis Virus (VSV), a member of the Rhabdoviridae family. It causes painful blister-like lesions (vesicles) on the mouth, lips, tongue, and occasionally on the coronary bands, teats, and sheath. The disease is notifiable in many countries — including the UK — because its clinical signs are indistinguishable from those of Foot and Mouth Disease (FMD), a devastating disease of cloven-hooved livestock, requiring laboratory confirmation to rule out FMD whenever vesicular disease is suspected.
VSV affects horses, donkeys, mules, cattle, pigs, and occasionally humans, making it a zoonotic concern. Outbreaks occur predominantly in the Americas — particularly the western United States and parts of Central and South America — and are strongly seasonal, appearing in summer and early autumn when insect vector populations peak. The disease is rare in Europe and the UK but must be considered in horses returning from endemic regions.
What Causes Vesicular Stomatitis in Horses?
VSV exists as two main serotypes — VSV-Indiana and VSV-New Jersey — both of which can cause clinical disease in horses. The virus is transmitted primarily through biting insects:
- Black flies (Simulium spp.): Major vector in North America, particularly during outbreaks
- Sand flies (Phlebotomus spp.)
- Biting midges (Culicoides spp.)
The virus can also spread through:
- Direct animal-to-animal contact with oral secretions or fluid from vesicles
- Contaminated equipment, feed bunks, water troughs, and tack
- Handlers who have been in contact with infected animals
The incubation period is 2–8 days. VSV can remain viable in the environment for several days under favourable conditions.
Signs and Symptoms of Vesicular Stomatitis in Horses
Clinical signs typically begin with fever and progressing to vesicular lesion formation:
- Fever: 38.9–40.6°C, often the first sign, appearing 1–3 days before visible lesions
- Excessive salivation (ptyalism): Drooling is often conspicuous and an early warning sign
- Vesicles and erosions: Fluid-filled blisters develop on the lips, tongue, gums, hard palate, and around the nostrils. These rapidly rupture, leaving painful erosions and ulcerations.
- Reduced feed and water intake: Oral pain makes eating and drinking very uncomfortable; weight loss can occur with prolonged inappetence.
- Coronary band lesions: Some horses develop vesicles at the coronary band, which can cause lameness as they rupture and ulcerate
- Teat lesions: In mares that are nursing, vesicles may form on the teats, causing pain and reluctance to allow the foal to nurse
- Sheath lesions: Occasional vesicles on the sheath and prepuce in males
- Loss of condition: Due to reduced feed intake and discomfort
The condition usually runs its course in 1–2 weeks in most horses, with vesicles healing once they rupture and re-epithelialise. However, secondary bacterial infections can complicate recovery.
Diagnosis
Vesicular stomatitis must be reported and is a differential diagnosis for FMD whenever vesicular lesions are found. Do not attempt to manage this condition as a routine oral problem without veterinary input.
- Notifiable disease reporting: In the UK and EU, any suspicion of VS or FMD must be reported to the relevant government veterinary authority (APHA in the UK) immediately. Movement restrictions and quarantine will be imposed pending laboratory results.
- Virus isolation: Samples from intact vesicle fluid, vesicle epithelium, or the margins of erosions submitted to approved laboratories for virus isolation and identification confirm VS and differentiate from FMD.
- PCR testing: Rapid PCR assays for VSV are available and provide faster results than virus isolation.
- Serology: Complement fixation tests or virus neutralisation tests can demonstrate rising antibody titres between acute and convalescent samples.
Treatment of Vesicular Stomatitis in Horses
There is no specific antiviral treatment for VSV. Management is supportive:
- Pain management: NSAIDs (phenylbutazone or flunixin meglumine) to manage oral pain, reduce fever, and encourage eating and drinking. Adequate pain relief is important to prevent secondary weight loss from inappetence.
- Oral care: Rinse the mouth with dilute antiseptic solutions (dilute chlorhexidine or iodine) to keep lesions clean and reduce secondary bacterial colonisation.
- Soft or liquid feed: Offer soaked hay, mashes, or grass to make eating more comfortable during the period of oral lesion activity. Ensure clean, fresh water is readily available.
- Wound care for coronary band lesions: Clean and dress any coronary band erosions to prevent secondary bacterial infection. Minimise movement on hard ground if lameness is present.
- Antibiotics: Systemic or topical antibiotics may be prescribed if secondary bacterial infection is confirmed or strongly suspected.
- Quarantine: Affected horses should be isolated from other livestock. Implement strict biosecurity protocols — separate feeding and watering equipment, dedicated overclothing for attendants, footbaths at stable entrances.
- Insect control: Reduce insect access to affected and in-contact horses through stabling at dusk and dawn, fly rugs and masks, and insect repellents.
Prevention of Vesicular Stomatitis in Horses
There is no licensed vaccine for VSV available in the UK or most European countries. Prevention focuses on:
- Biosecurity for travelling horses: If horses are travelling to or from endemic regions (USA, Mexico, Central America), be aware of the disease and observe appropriate post-travel monitoring. Do not import horses from active outbreak areas without veterinary clearance.
- Insect control: Comprehensive fly and biting insect control measures reduce the risk of vector transmission. This is most relevant in endemic areas during the summer insect season. Stable horses at dusk and dawn when black fly activity peaks.
- Equipment hygiene: Disinfect shared tack, bits, feed buckets, and other equipment regularly. Do not share equipment between horses without decontamination.
- Reducing animal-to-animal contact: Separate new arrivals and monitor for signs of illness for at least 2 weeks before introducing them to the resident herd.
Zoonotic Risk
VSV is a zoonotic pathogen — it can infect humans, primarily through direct contact with vesicle fluid, saliva, or nasal secretions from infected animals. In humans, VSV typically causes a flu-like illness with vesicles on the hands, mouth, or around the lips. The disease in humans is usually self-limiting and not serious, though immunocompromised individuals may be more severely affected. Wear gloves when handling any horse with vesicular lesions. Report any human illness following contact with suspected VS cases to your GP.
Prognosis
The prognosis for equine vesicular stomatitis is generally good. Most horses recover fully within 2–3 weeks once lesions heal. Serious complications are uncommon in otherwise healthy horses. Secondary bacterial infections of oral lesions or coronary band wounds can prolong recovery. Horses with coronary band lesions may show temporary lameness that resolves as the wounds heal. There are no long-term sequelae in most recovered horses. Economic and operational impact — particularly the enforced quarantine and movement restrictions — may be the most significant practical consequence for affected premises.
When to Call the Vet
Contact your vet immediately if you observe:
- Vesicles or blisters in or around the mouth of any horse, donkey, or mule
- Lesions on the coronary bands with or without lameness
- Excessive salivation combined with reduced appetite
- Fever combined with the above signs
Do not wait for signs to develop further before calling — vesicular stomatitis is a notifiable disease, and rapid reporting and isolation are legally required and ethically important to prevent spread to other livestock.
Frequently Asked Questions
Is vesicular stomatitis the same as Foot and Mouth Disease?
No, but it can look identical clinically. VSV and FMD are caused by completely different viruses — FMD only affects cloven-hooved animals (not horses primarily), while VSV affects horses, cattle, and pigs. Horses are not susceptible to FMD virus, but because the lesions look the same, any suspicion of vesicular disease in any livestock species requires laboratory testing to confirm the diagnosis. In the UK, this is managed as a notifiable disease investigation.
Can horses get vesicular stomatitis in the UK?
It is rare but possible — primarily a risk for horses returning from endemic areas (USA, Mexico, Central and South America) or via contaminated equipment. Insect vector requirements mean outbreaks in the UK climate are unlikely but cannot be completely ruled out. Any horse returning from the Americas should be monitored for signs consistent with VS for at least 14 days after return.
How is VSV spread to humans?
Transmission to humans occurs through direct contact with an infected animal’s saliva, vesicle fluid, or nasal secretions — typically when handling affected horses without appropriate protective equipment. The virus can enter through cuts or abrasions on the hands, or through mucous membranes. Wearing gloves and practising thorough hand hygiene when handling any horse with vesicular lesions effectively eliminates the risk of human infection in most cases.
How long are horses contagious with vesicular stomatitis?
Horses are contagious while they have active vesicular lesions — typically for 7–14 days. Shedding of virus in saliva and nasal secretions begins a few days before lesions are visible. Horses should remain in quarantine until all lesions have fully healed and they have been cleared by the relevant veterinary authority. Premises may also face movement restrictions for several weeks after the last case resolves.