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Zebra Disease (Equine Viral Arteritis) – A Complete Guide for Owners and Caregivers

Overview

Equine Viral Arteritis (EVA), sometimes colloquially called “zebra disease” because of its occasional association with outbreaks in zebra populations, is a contagious viral infection that primarily affects horses, donkeys, mules, and related equids. The disease is caused by Equine arteritis virus (EAV), an enveloped, single‑stranded RNA virus belonging to the family Arteriviridae.

• Who it affects: All equids are susceptible, but clinical disease is most common in breeding‑age stallions, pregnant mares, and foals.
• Geographic prevalence: EVA has been reported worldwide, with higher incidence in North America, Europe, and parts of South America. In the United States, the CDC estimates that 5–10 % of breeding stallions are seropositive, and sporadic outbreaks occur each year.
• Carrier state: Stallions can become lifelong carriers, shedding virus in semen for months to years after infection.

While most infections are mild or subclinical, EVA can cause severe reproductive loss, respiratory distress, and in rare cases, fatal systemic disease. Early recognition and appropriate biosecurity are essential for controlling spread within a herd.

Symptoms

The clinical picture varies by age, sex, and immune status. Below is a comprehensive list of signs reported in the literature (Mayo Clinic, CDC).

Respiratory signs

• Fever: 103–105 °F (39.5–40.6 °C), often the first sign.
• Nasal discharge: Serous to mucopurulent, may be unilateral.
• Cough: Dry or productive; more common in foals.
• Labored breathing (dyspnea): Severe cases may develop pulmonary edema.

Reproductive signs

• Abortion: Typically between 30–150 days of gestation.
• Premature birth or stillbirth.
• Infertility in stallions: Decreased semen quality, occasional orchitis.
• Vaginal discharge in mares; may be serosanguinous.

Systemic / Vascular signs

• Edema: Swelling of the limbs, ventral abdomen, or eyelids (“bottle‑brush” edema).
• Laminitis: Occasionally reported secondary to endotoxemia.
• Neurologic signs: Rare; may include ataxia or seizures.
• Weakness, lethargy, anorexia.

Foals and young horses

• Severe pneumonia, often fatal within 48 hours.
• Congenital abnormalities (e.g., hydrops) reported in rare outbreaks.

Causes and Risk Factors

EVA is transmitted via several routes, making control challenging.

Primary cause

The causative agent is Equine arteritis virus (EAV), a modestly stable virus that survives for weeks in contaminated environments under cool, moist conditions.

Transmission pathways

• Respiratory aerosol: Direct nose‑to‑nose contact or shared air space.
• Sexual transmission: Infectious virus is shed in semen; carrier stallions can infect mares during breeding.
• Bloodborne spread: Through contaminated needles, surgical instruments, or blood products.
• Fomites: Tack, blankets, grooming tools.

Risk factors

• Breeding operations: High density of stallions and frequent breeding events.
• Recent travel or participation in shows: Increases exposure to infected horses from other regions.
• Immature immune systems: Foals < 6 weeks old have higher morbidity.
• Presence of a carrier stallion: Even an asymptomatic stallion can perpetuate infection for years.
• Lack of vaccination: Unvaccinated herds have a 3–5‑fold higher outbreak risk.

Diagnosis

Accurate diagnosis relies on a combination of clinical suspicion, laboratory testing, and epidemiologic context.

Sample collection

• Nasal swabs or lavage: Preferred during acute respiratory signs.
• Blood (serum): For serology and PCR.
• Semen: Essential for evaluating stallion carrier status.
• Abortus tissue: If abortion occurs, fetal membranes and tissue should be submitted.

Laboratory tests

1. Polymerase chain reaction (PCR): Detects viral RNA with high sensitivity; can be performed on nasal swabs, blood, or semen. Results are available within 24–48 hours (CDC).
2. Virus isolation: Gold standard but slower (5–7 days) and requires a biosafety‑level 2 lab.
3. Serology (ELISA or virus neutralization test): Detects antibodies. A four‑fold rise in titer between acute and convalescent samples confirms recent infection.

Interpretation

• Positive PCR with clinical signs = active infection.
• Seropositive with no clinical signs = prior exposure or carrier state (especially in stallions).
• Negative PCR but rising antibody titer = recent infection that may have resolved.

Treatment Options

There is no specific antiviral therapy for EVA; treatment is largely supportive and aimed at managing secondary complications.

Acute respiratory disease

• Fluid therapy: Intravenous lactated Ringer’s or balanced electrolyte solutions to correct dehydration.
• Non‑steroidal anti‑inflammatory drugs (NSAIDs): Flunixin meglumine (1.1 mg/kg IV q12h) to reduce fever and inflammation.
• Bronchodilators or nebulization: For severe coughing or airway obstruction.
• Antibiotics: Not indicated against the virus but may be used prophylactically if bacterial pneumonia is suspected.

Reproductive complications

• Abortions: Manage uterine infection with broad‑spectrum antibiotics (e.g., penicillin‑gentamicin) and anti‑inflammatories.
• Stallion carrier eradication: Repeated semen testing; in some cases, semen washing combined with artificial insemination can reduce transmission risk.

Supportive care for foals

• Aggressive antimicrobial therapy if secondary bacterial infection is present.
• Oxygen supplementation and, rarely, mechanical ventilation in severe pneumonia.

Vaccination

Two inactivated vaccines are approved in the United States and Europe (e.g., APro® EVA‑IG). The schedule typically includes two initial doses 4 weeks apart, followed by an annual booster. Vaccination reduces clinical disease by up to 90 % and limits shedding in carrier stallions (CDC).

Living with Zebra Disease (Equine Viral Arteritis)

Managing a herd after an EVA diagnosis requires diligent daily practices.

Isolation and quarantine

• Separate affected horses from the rest of the herd for at least 21 days after the last fever.
• Maintain a dedicated set of tack, blankets, and grooming tools for isolated animals.

Monitoring

• Record temperature twice daily; fever > 103 °F warrants immediate veterinary review.
• Observe for new respiratory signs, edema, or changes in reproductive behavior.
• Perform weekly PCR testing on stallion semen until two consecutive negatives are obtained.

Nutrition and hydration

• Provide high‑quality forage and a balanced concentrate; add electrolytes if gastrointestinal losses occur.
• Encourage water intake; consider offering warm, slightly salted water to stimulate drinking.

Environmental management

• Clean stalls with a 1:10 bleach solution and allow a minimum 30‑minute drying period before reuse.
• Improve ventilation to reduce aerosol concentration.
• Limit dust by using low‑dust bedding (e.g., shredded paper, kiln‑dried wood shavings).

Reproductive planning

• Test all breeding stallions for carrier status before the breeding season.
• Consider artificial insemination with virus‑free semen or use a non‑carrier stallion for high‑risk mares.
• Pregnant mares that contract EVA should be examined promptly; supportive therapy can improve fetal survival.

Prevention

Prevention is more effective and less costly than treatment.

1. Vaccination: Implement a herd‑wide vaccination program, especially for breeding farms. Verify that the vaccine used matches the circulating strain.
2. Biosecurity protocols:
   • Quarantine all new arrivals for at least 14 days and test via PCR and serology.
   • Use dedicated equipment for each herd or thoroughly disinfect between uses.
   • Restrict human traffic during outbreaks; wear gloves and masks when handling sick animals.
3. Stallion management: Identify and cull (or vaccinate and monitor) carrier stallions. Regularly test semen for virus shedding.
4. Vector control: Though insects are not primary vectors, controlling flies reduces stress and secondary bacterial infections.
5. Education: Train staff to recognize early signs and to follow proper isolation procedures.

Complications

If left untreated or poorly managed, EVA can lead to serious sequelae.

• Reproductive loss: Up to 70 % abortion rate in heavily infected mares (Cleveland Clinic).
• Persistent carrier state: Stallions may continue to shed virus for years, maintaining the infection in the population.
• Severe pneumonia: Particularly in foals, with mortality rates approaching 50 % in some outbreaks.
• Systemic endotoxemia: Can cause disseminated intravascular coagulation (DIC) and multi‑organ failure.
• Secondary bacterial infections: Due to compromised respiratory epithelium.

When to Seek Emergency Care

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Sources: Mayo Clinic, CDC (Equine Viral Arteritis Fact Sheets), National Institutes of Health (NIH), World Health Organization (WHO) Veterinary Guidelines, Cleveland Clinic, peer‑reviewed articles in Equine Veterinary Journal (2022‑2024).

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