Camelidae and Cervidae Vesicular Stomatitis Study Guide

Overview and Clinical Importance

Vesicular stomatitis (VS) is a viral, vector-borne disease affecting multiple livestock species in the Americas. While primarily affecting horses and cattle, New World camelids (llamas and alpacas) are susceptible species with documented cases. Cervids (deer species) demonstrate serological evidence of exposure but rarely develop clinical disease in natural settings.

VS is caused by vesicular stomatitis virus (VSV), a bullet-shaped rhabdovirus in the genus Vesiculovirus. Two serotypes affect livestock in North America: New Jersey (VSV-NJ) and Indiana (VSV-IN).

Etiology and Pathophysiology

Viral Characteristics

Vesicular stomatitis virus belongs to the family Rhabdoviridae, genus Vesiculovirus. The virus is enveloped, bullet-shaped, and contains a single-stranded, negative-sense RNA genome approximately 180 nm long and 75 nm wide.

The viral genome contains five genes encoding: nucleocapsid protein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G), and large polymerase protein (L).

VSV Serotypes and Characteristics

Epidemiology

Geographic Distribution: VSV is endemic in Central America, South America, and parts of Mexico. In the United States, outbreaks occur sporadically every 2-10 years, primarily in western and southwestern states.

Seasonal Pattern: Outbreaks typically occur during warmer months (May through October) when insect vectors are active. Disease activity ends with freezing temperatures that kill vector populations.

Reservoir Hosts: No definitive reservoir host has been identified. Many wildlife species show serologic evidence of exposure, including cervids, but their role in viral maintenance remains unclear.

Transmission

Primary Vector Transmission:

• Black flies (Simuliidae) - most important vectors in southwestern US
• Sand flies (Phlebotominae) - important in endemic regions
• Biting midges (Ceratopogonidae) - competent vectors

Direct Transmission:

• Contact with vesicular fluid from active lesions
• Contaminated feed and water sources
• Shared equipment and milking procedures (dairy cattle)

Species Susceptibility and Clinical Signs

Camelidae (Llamas and Alpacas)

New World camelids (llamas and alpacas) are naturally susceptible to vesicular stomatitis virus. They are the third most commonly affected species after horses and cattle in US outbreaks.

Clinical Presentation in Camelids

Incubation Period: 2-8 days following exposure, often preceded by fever.

Early Signs:

• Excessive salivation (ptyalism) - often the first noticed sign
• Reluctance to eat or decreased appetite
• Fever (typically resolves before other signs become apparent)

Vesicular Lesions:

• Oral cavity: Vesicles on lips, gums, tongue, and dental pad that rapidly rupture
• Muzzle and nostrils: Crusting lesions and erosions
• Coronary band: Erosive lesions that may cause lameness
• Other sites: Ventral abdomen, ears, sheath, or vulva

Clinical Progression in Camelids

Cervidae (Deer Species)

Cervids including white-tailed deer, mule deer, elk, and other species show serological evidence of VSV exposure but rarely develop clinical disease in natural settings.

Clinical Status in Cervids

Natural Infections: No confirmed clinical cases of vesicular stomatitis have been reported in wild cervids in the United States, despite experimental susceptibility.

Serologic Evidence: Antibodies to VSV have been detected in multiple cervid species including deer, pronghorn antelope, and bighorn sheep, indicating exposure without clinical disease.

Potential Role: Cervids may serve as sentinels for virus circulation in the environment or as subclinical amplifying hosts, but their exact role in the epidemiology remains undefined.

Differential Diagnosis

Critical Importance: Vesicular stomatitis is clinically indistinguishable from foot-and-mouth disease (FMD) in ruminants. Prompt and accurate diagnosis is essential to prevent catastrophic trade restrictions and economic losses.

Primary Differentials by Species

Diagnosis

Sample Collection

Vesicular stomatitis is a reportable disease. Contact state or federal animal health officials immediately for suspected cases. Samples must be collected by trained personnel.

Preferred Samples:

• Vesicular fluid from intact vesicles (best option but rarely available)
• Epithelial flaps from fresh vesicles or erosions
• Swabs from fresh lesions (use viral transport media)
• Paired serum samples (acute and convalescent, 14-21 days apart)

Laboratory Testing

Treatment and Management

Treatment Approach

No specific antiviral treatment is available for vesicular stomatitis. Management focuses on supportive care, pain relief, and prevention of secondary complications.

Supportive Care by System

Prognosis

Excellent for uncomplicated cases: Most animals recover completely within 10-21 days. Mortality is rare and typically associated with secondary complications.

Factors Affecting Recovery:

• Age and body condition at onset
• Severity and location of lesions
• Development of secondary bacterial infections
• Adequacy of supportive care and nutrition

Prevention and Control

Vector Control

Insect management is the primary prevention strategy since no vaccines are commercially available for vesicular stomatitis.

Environmental Management:

• Eliminate standing water sources where possible
• Maintain distance from irrigation ditches, creeks, and rivers
• House animals indoors during peak insect activity (dawn and dusk)
• Install fans in barns and stalls to discourage flying insects

Topical Protection:

• Insecticide-treated ear tags for large animals
• EPA-approved insect repellents for targeted application
• Protective fly sheets and masks for high-risk periods

Biosecurity Measures

Movement Restrictions: Quarantine affected premises until 14 days after all lesions have healed and no new cases occur.

Equipment Disinfection:

• Clean and disinfect all equipment between animals
• Use 1% sodium hypochlorite (bleach) or commercial virucides
• Separate feed and water sources for affected animals

Personnel Protection: VSV is zoonotic. Use personal protective equipment when handling lesioned animals.

Regulatory Considerations

Reporting Requirements

Vesicular stomatitis is a federally reportable disease in the United States. Any suspected case must be reported immediately to:

• State veterinarian or animal health official
• USDA Area Veterinarian in Charge (AVIC)
• Federal emergency hotline: 1-866-536-7593

Economic Impact

VS outbreaks result in significant economic losses due to quarantines, movement restrictions, and trade impacts. The 2019-2020 outbreak affected over 1,100 premises across 8 states.

Exam Focus: Remember the regulatory pyramid: VS = Veterinarian → State Veterinarian → USDA. Immediate reporting is critical because VS mimics FMD. Know that horses can get VS but NOT FMD - this is the key distinguishing clinical feature.