Vesicular stomatitis (VS) is a viral disease that primarily affects livestock, including horses, cattle, and swine. The disease is caused by the Vesicular Stomatitis Virus (VSV), a member of the Rhabdoviridae family, which is recognized for its characteristic bullet shape. Vesicular stomatitis is classified as a zoonotic disease, meaning it is transmissible from animals to humans, though human cases are generally infrequent and occur mainly in individuals working closely with infected animals. While concerning for animal commerce due to quarantines and trade restrictions, the infection in humans is typically mild and self-limiting.
The Primary Disease in Livestock
The disease in animals is marked by the formation of fluid-filled blisters, known as vesicles, which are the source of the virus’s name. These painful lesions typically develop on the tongue, inside the mouth, on the muzzle, the coronary band just above the hooves, and sometimes on the teats of dairy cattle. The vesicles soon rupture, leaving behind raw, ulcerated areas that cause animals to drool excessively or refuse to eat and drink due to the discomfort.
In horses, the lesions in the mouth and on the coronary band can lead to lameness and difficulty eating, which results in weight loss. For cattle, lesions on the teats can open the way for secondary bacterial infections like mastitis, causing a severe drop in milk production and significant economic losses for farmers. A major concern for regulatory officials is that the clinical signs of vesicular stomatitis are virtually indistinguishable from Foot-and-Mouth Disease (FMD) in cattle and swine. Because FMD is a highly contagious disease foreign to many countries, a suspected VS case requires immediate reporting and regulatory action, including quarantine and laboratory testing, until FMD is ruled out.
How Vesicular Stomatitis Spreads to People
The transmission of Vesicular Stomatitis to humans involves two primary routes: direct contact and vector-borne spread. Direct infection most commonly occurs when people handle livestock that are showing clinical signs of the disease, such as ruptured blisters or excessive saliva. The virus enters the human body through breaks in the skin, such as cuts or abrasions, or through contact with mucous membranes of the eyes, nose, or mouth.
The virus is also considered an arbovirus, meaning it can be transmitted by arthropod vectors. Biting insects, particularly sand flies and black flies, have been identified as capable of transmitting the virus, especially during warmer months when outbreaks are most common. The virus may also be spread indirectly through contaminated objects, known as fomites, such as equipment, water troughs, or feed.
Clinical Signs of Human Infection
When a person contracts the virus, the symptoms generally resemble a mild, acute influenza-like illness. The incubation period is typically short, ranging from two to eight days after exposure. Infected individuals often experience a sudden onset of symptoms, including fever, headache, muscle aches, and a general feeling of discomfort and weakness.
The severity of these flu-like symptoms can vary, sometimes including chills, nausea, or retrosternal chest pain. Less commonly, some individuals may develop small, blister-like lesions, or vesicles, on the lips, nose, or inside the mouth, similar to the sores seen in animals. The disease is self-limiting, meaning it resolves on its own without specific medical treatment, and most people recover fully within four to seven days. While severe complications like encephalitis are extremely rare, they have been reported, primarily in specific serotypes or in immunocompromised individuals.
Preventing Human Exposure
Preventing human infection relies heavily on implementing strict hygiene and personal protective measures, particularly for individuals who work with livestock. Veterinarians and animal handlers should use Personal Protective Equipment (PPE), including disposable gloves, eye protection, and protective clothing, when examining or treating animals with suspected lesions. Handwashing with soap and water should be performed frequently, especially immediately after any contact with animals, their secretions, or contaminated equipment.
Insect control measures are also an important part of prevention, given the role of biting flies in the transmission cycle. This involves eliminating or reducing insect breeding areas and using approved insecticides on animals and around premises. Prompt reporting of suspected animal cases to state or federal animal health officials, such as the USDA, is important to initiate quarantine procedures. Quarantining affected premises helps contain the outbreak, minimizing the chance of human exposure to the virus.