Equine Vesicular Stomatitis Study Guide

Overview and Clinical Importance

Vesicular stomatitis (VS) is a contagious viral disease caused by vesicular stomatitis virus (VSV), primarily affecting horses, cattle, and swine in the Western Hemisphere. VS is characterized by vesicular lesions affecting the oral mucosa, tongue, coronary bands, and other mucocutaneous areas. It is a reportable disease of significant economic and regulatory importance due to its clinical similarity to foot-and-mouth disease.

Etiology and Pathophysiology

Viral Characteristics

Vesicular stomatitis virus (VSV) belongs to the family Rhabdoviridae, genus Vesiculovirus. The virus is an enveloped, single-stranded RNA virus with a characteristic bullet-shaped virion measuring approximately 180 nm long and 75 nm wide.

Pathophysiology

VSV enters the body through breaks in mucosa or skin, commonly caused by rough forage or arthropod bites. Localized viral infection of epithelial cells leads to intraepithelial edema and vesicle formation, which rapidly rupture to form ulcerative lesions.

Epidemiology and Transmission

Geographic Distribution

VSV is limited to the Western Hemisphere. Endemic areas include southern Mexico, Central America, and northern South America. In the United States, sporadic outbreaks occur primarily in southwestern states (Colorado, New Mexico, Texas, Wyoming) during warmer months.

Transmission Mechanisms

Primary transmission: Arthropod vectors including black flies (Simulium vittatum), sand flies (Lutzomyia shannoni), and biting midges (Culicoides spp.)

Secondary transmission: Direct contact with lesion exudate, contaminated equipment, and fomites during active disease

Clinical Signs and Lesion Distribution

Incubation Period and Initial Signs

Incubation period: 2-8 days post-exposure with initial fever (often subsided by examination)

First clinical sign: Excessive salivation (ptyalism), drooling, or frothing at the mouth due to painful oral lesions

Characteristic Lesion Distribution

Diagnosis and Laboratory Testing

Clinical Diagnosis

Initial diagnosis is based on recognition of characteristic vesicular lesions in susceptible species during appropriate seasons (May-October). Clinical signs alone are insufficient for definitive diagnosis due to similarity with other vesicular diseases.

Laboratory Confirmation

Reporting Requirements

Vesicular stomatitis is a reportable disease in most areas including the United States. Veterinarians must immediately notify state and federal animal health officials of suspected cases. Samples are submitted to NVSL (Ames, Iowa) for equine cases or to approved National Animal Health Laboratory Network laboratories during outbreaks.

Differential Diagnosis

Treatment and Management

Treatment Protocols

No specific antiviral treatment exists for vesicular stomatitis. Management focuses on supportive care and prevention of secondary complications.

Prognosis

The prognosis for equine vesicular stomatitis is generally excellent. The disease is self-limiting, resolving within 10-14 days in most cases. Complications are rare but may include secondary bacterial infections, severe weight loss in debilitated animals, or laminitis from coronary band lesions.

Prevention and Control Measures

Vector Control

Primary prevention focuses on reducing exposure to arthropod vectors:

• House animals during peak vector activity (dawn and dusk)
• Use insect repellents and insecticide-treated ear tags
• Eliminate standing water and vector breeding sites
• Install physical barriers like screens in barns

Quarantine and Biosecurity

Upon confirmation of vesicular stomatitis, premises are placed under state quarantine for minimum 14 days from onset of lesions in the last affected animal.

• Isolate affected animals immediately
• Restrict animal movement to/from affected facilities
• Disinfect equipment, vehicles, and surfaces
• Use individual feed/water buckets and grooming equipment

Vaccination Status

No vaccines are currently licensed for vesicular stomatitis in the United States due to the sporadic nature of outbreaks and excellent recovery rate. Vaccines are available in some Latin American countries where the disease is endemic.

Zoonotic Considerations and Public Health

Human Infection Risk

Vesicular stomatitis is zoonotic and can be transmitted to humans through direct contact with lesion exudate, saliva, or contaminated materials. Human infections are most common among:

• Veterinarians and veterinary staff
• Laboratory workers handling virus
• Livestock handlers and farm workers

Clinical Signs in Humans

Incubation period: 1-6 days in humans

Most common presentation: Influenza-like illness lasting 3-5 days including fever, headache, myalgia, malaise, and fatigue

Rare presentations: Vesicular lesions on lips, oral mucosa, or nose; severe cases may include encephalitis (extremely rare)

Personal Protective Equipment

MANDATORY PPE when handling suspected or confirmed VSV cases:

• Disposable gloves (nitrile or latex)
• Eye protection (safety glasses or goggles)
• Face masks when performing procedures
• Protective clothing or coveralls
• Proper hand hygiene with antiseptic soap

Essential Points for NAVLE Success

• Vesicular stomatitis is a reportable viral disease affecting horses, cattle, and swine
• Horse involvement differentiates VS from foot-and-mouth disease (horses resistant to FMD)
• Characteristic lesion pattern: oral mucosa + coronary bands + other mucocutaneous sites
• Transmitted by arthropod vectors (black flies, sand flies, biting midges)
• Seasonal disease (May-October) in southwestern United States
• Self-limiting disease with excellent prognosis (10-14 day recovery)
• Treatment is supportive; no specific antiviral therapy
• Zoonotic potential - PPE required when handling affected animals
• Immediate reporting to authorities is legally mandated
• 14-day quarantine minimum after last affected animal recovers