Vesicular Stomatitis

By Garrett Metcalf, DVM

There are four vesicular diseases that can cause illness in various livestock species. Some of the vesicular disease can cause some very serious consequences to the animal and to the industry, hence why these diseases are monitored very closely by veterinarians at federal, state and local levels. Some of these vesicular diseases are classified as foreign animal diseases meaning that we do not have them in the United States and we want to keep it that way. Vesicular Stomatitis (VS) is the only vesicular disease currently in the United States that can affect mostly horses but also cattle, pigs, alpacas, llamas, sheep, goats and even humans. Because all vesicular disease look similar and are indistinguishable without testing makes it important for monitoring and tracking. If one of the other three vesicular disease was to be introduced into the United States we would not know it quickly enough if it wasn’t for tracking of VS.

Vesicular diseases are caused by viruses that make similar blister like lesions on various parts of the body making them indistinguishable. The other three diseases are Foot –and-Mouth, Swine Vesicular Disease and Vesicular Exanthema of Swine. None of them sound very scary but they can have serious impact on the livestock industry and the economy if there was to be an outbreak of these disease. Since VS is here in the United States it is necessary to monitor the spread, prevent spread and test those animals that show signs to make sure it is VS and not one of the other three diseases. Luckily horses are not affected by the other three vesicular diseases but it is still important for monitoring and control of VS to protect other species that are susceptible to other forms of vesicular diseases.

Clinical Signs in Horses

VS causes blister like lesions in the mouth, tongue, ears, around the feet, udders and sheath as well. Horses that are infected will have symptoms of fever, lethargy, not eating, lameness and drooling from the mouth because of the irritation and inflammation caused by the virus. Horses may be rubbing their muzzle or mouth on objects. The clinical signs and lesions are enough to raise suspicion and warrant testing.  The incubation period is approximately 2-8 days from the time they get exposed to the time they show the disease. One of the most obvious signs is the drooling and frothing from the mouth. The lesions or blisters will contain the virus and is the source to spread to other animals or people that come in contact with vesicular fluid.  

Transmission and Testing –

VS is most commonly transmitted by flies that like to collect around the face and mouth of horses. The most common species to transmit VS are black flies, sand flies and midges. The disease can also spread by contact with objects shared between animals such as water buckets, tack, halters, grooming equipment and other shared surfaces where vesicular fluid from the wounds came in contact. Transmission is more common during warmer parts of the year and has a seasonal cycle. The spread of the disease is sporadic and has brought into question how it is spread but for the most part seems to be through an insect vector.

Laboratory testing is required to either isolate the virus from the lesions or test for antibodies in the blood of an infected horse.  After reporting the suspected case to state/federal officials, the testing samples are collected and submitted to confirm if the disease is VS.

Treatment –

With most viral disease in animals or humans supportive care is the key to get them through it. The oral lesions can be the most detrimental to the horse causing reluctance to eat or drink leading to dehydration and starvation. Feeding a soft diet of feeds and chopped hay or green grass can help them to continue to get nutrition. Controlling pain and inflammation with anti-inflammatory drugs is important to keep horses comfortable and willing to eat. Pain management is also important with coronary band lesions that cause lameness and possible laminitis. Bacterial infections from ulcerative lesions can be a concern especially with persistent fevers and drainage from the wounds necessitating antibiotics for secondary bacterial infections.

Thankfully the disease is self limiting and typical runs its course in 14 days. The morbidity is high around 90% and the mortality is low. The disease is a reportable disease and requires isolation, biosecurity and quarantining measures to prevent the spread of the disease to other horses. The guidelines and protocols are put into place by state veterinarians once a suspected case is reported to them. A quick rule to follow to prevent the spread of this disease is to isolate sick horses, care and treat for the sick last and use good insect control measures. Using protective equipment is important to prevent the spread to other horses and to protect any persons handling infected horses from transmitting the disease. Symptoms in people are flu-like symptoms, fever and rarely oral lesions.

Prevention –

There is no vaccine for VS so the only method of protecting your horse is to prevent exposure to VS infected horses. It is recommended to isolate new horses that come into the herd or onto property when other horses are present.  During outbreaks of VS, certificate of veterinary inspection (CVI) is used to help prevent the spread of the disease in large groupings of horses or events and movement of horses to and from other states. Currently the CVI is only issued for 5 days when horses come from a county that has a confirmed case of VS. States to state requirements are different so it is important to talk to your local veterinarian before traveling to other states and the requirements of the CVI in that state or county.

VS is an important disease for horses owners to be aware of especially during times of outbreak like we are experience in Oklahoma currently. Fortunately the disease is self limiting and with supportive care has a low mortality rate. It’s important if a horse is suspected to have signs or symptoms of VS to isolate the horse from other horses and contact your veterinarian for examination to determine if testing is indicated.

Read more in the September issue of Oklahoma Farm & Ranch.