Tuesday, December 19, 2006

Equine Herpes Virus Outbreak

For those who have not "herd" through the horseshow telegraph ....there has been an outbreak of neurologic herpes virus in South Florida (Wellington ). I have touched on this topic in the past but felt it was important to put up some current data and dispel some of the rumors. NeurologicEHV-1 virus (Rhinopneumonitis), the one that causes respiratory disease and abortions in mares, is the virus that causes the neurologic form. It is one of the typical vaccines we give ( flu/rhino). The respiratory tract is the natural portal of entry for EHV-1 and EHV-4, and the respiratory mucosal epithelium is the primary target tissue for infection [2,28,29]. Respiratory infection is acquired by close physical contact with another horse that is actively shedding infectious virus into its respiratory secretions. Virus-laden droplets generated by forced, high-velocity expirations through the airways (snorting) can produce infective aerosols capable of traveling over short distances (between box stalls, fenced paddocks, etc). The efficiency of aerosol transmission and the consequent capacity for rapid spread of herpesvirus infections are generally less than those exhibited by equine influenza virus. EHV-1 is a herpes virus and like most herpes it can reside in the patients neural tissue for VERY long periods of time to recrudesce or come out during periods of stress. The latent carrier state is critically important to the maintenance and spread of EHV-1 and EHV-4 and to their success as widespread, deeply entrenched pathogens of the horse. Because herpesvirus latency is a reversible state, the latent virus genome may become reactivated to regain its full transcriptional activity with a consequent production of infectious virus. Periodic reactivation of latent EHV-1 and EHV-4 is associated with episodes of stress or corticosteroid administration [26,27]. The stimuli for herpesvirus reactivation are diverse and include surgery, boarding, parturition, prolonged transport, weaning, lactation, inclement weather, and social disruption. Reactivation of the latent herpesviruses may occur in the absence of concurrent clinical signs. Respiratory tract shedding from carrier horses in which latent virus has been reactivated has been documented, and shedding of reactivated virus into the respiratory mucus is often not accompanied by clinical signs [24]. Dr Long at the Univ of Fla recently posted some detailed info through the UF website with details for handling a suspected problem.You will find it and some links at the bottom of this post. The disease are probably a consequence of an infection of the endothelia of small blood vessels, which results in vasculitis and reactive thrombosis. The thrombosis in turn causes impaired microcirculation in affected areas, including oxygen deprivation (hypoxia) and finally neuronal death and neurologic disease. The big problem really,is should we vaccinate in the face of an infection or not. A study in Calif. found vaccinated horses were more likely to develop the neurologic form. However,one recent study from Cornell showed that the Modified live vaccine "Rhinomune" protected against the intra-nasal challenge ,whereas the killed vaccine did not. The vaccine was given in 2 doses 4 weeks prior to the challenge. Since you don't know when your horse might have been exposed this could pose a problem. My current thought on this is as follows. 1. vaccinate 2-3 times yearly with the Mod. Live vaccine. 2. practice good farm hygiene and isolation 3. avoid high risk areas. ( show grounds with a questionable history).
Since we haven't seen EHV-1 in this area this year and if none of your stablemates have been in South Florida, and your horse was appropriately vaccinated this summer,then we should be OK.
Watch for any nasal discharge or horses with a fever and isolate them accordingly and contact us. Read the following info closely and apply the information to your farm as best as possible.

Neurological EHV-1

Outbreak Information

Biosecurity Guidelines

THESE GUIDELINES are adopted from


Ask your veterinarian to download instructions in Spanish from this website!


Remember that an important rule out for neurological disease is rabies; consider neurological horses as rabies suspects

  1. Assign specific individuals to care for affected horses
  2. If this is not possible, work on healthy, exposed, then sick horses last
  3. Use personal protection equipment: gloves, booties, tyvek suit (http://www.galeton.com/tyveksuit.asp)
  4. After handling sick horse: dispose of covering or clothing in lidded trash receptacle. If not disposable, place in container and wash daily with laundry detergent, fully dry.
  5. Wash hands under running water with soap for 15 seconds. Follow up with 62% ethyl alcohol hand gel or foam disinfectant. The latter can be used in place of hand washing.
  6. Caretakers should ideally be provided a changing area so clothing are not worn elsewhere if tyvek suits are not available.

Management Practices:

1. Post restricted access signs in English and Spanish at all perimeter access points.

2. Footbaths and hand sanitizers should be placed at all primary perimeter access points. Separate footwear to isolation barns is highly recommended.

3. Prevent all contact between horses. Cover all mesh with solid barriers consisting of plywood/plastic.

4. Do not allow horses to share water sources; clean buckets daily. Do not submerge hoses in water buckets.

5. Manure and bedding should not be placed in open air. Carts and wheelbarrows should be decontaminated between stalls or separate containers should be used. Do not spread manure on pastures.

6. Do not share equipment. Any shared equipment should be scrubbed and disinfected between use.

7. Any cloth materials should be laundered and dried completely.

8. Do not share medications between horses. Each horses has separate equipment for oral medications. ALWAYS use new needles and syringes for injectables. Wash hands after treating each horse.

Facilities and Trucks

1. Non-porous buildings are highly desirable for quarantine and management.

2. For cleaning wet down all surfaces without spraying. Scrub with brush and powdered laundry detergent or Dawn dish detergent. Let stand under soap for 10 minutes. Rinse with running water-no spray. Squeegee, allow to dry. Clean all aisles and common areas twice daily.

3. Perform same cleaning in wooded barns, however spend extra time removing debris and allow wood to completely dry. Painting wood is a good alternative for sealing wood surfaces.

4. Clean all trailers in same fashion between all loads.

Neurological EHV-1

Outbreak Information

Clinical Signs/Testing

Websites for Information





Contact Information:

Florida Department of Agriculture & Consumer Services; Dr. Michael Short 850-410-0900

Veterinarians with suspect cases of EHV-1 must report to FDACS immediately

Incubation Period: 1 to 10 days, primarily 1-3 days

Viral Shedding: 7-10 days, can be up to 28 days from onset of signs in some instances

Transmission: 1) nose to nose contact 2) people through contamination of hands and equipment 3) inanimate objects such as water buckets, bits, clippers, etc, 4) aborted placenta and fetal tissues.

Neurological horses are capable of shedding high amounts of virus

Environmental Contamination: Herpesviruses are easily inactivated with quaternary ammonium compounds (http://www.answers.com/topic/quaternary-ammonium-compound) or bleach (10%). Hand washing and soap/water washing of equipment will minimize contamination. However, without this, herpesviruses can persist in the environment for a week and sometimes for up to 30 days.

Horses can be clinically normal and still shed virus!

Clinical Signs:

Respiratory signs may be minimal and of short duration.

Increased rectal temperature may be the only clinical sign

Horses can have two fever spikes

The initial rise in rectal temperature is usually mild-101.5 to 102.5°F

After the initial temperature rise, which may be missed, the horse can either be clinical normal, develop respiratory signs of nasal discharge, increased temperature (> 102.5), minimal coughing, can abort if pregnant, or, in a small number of cases develop neurological signs.

Neurological signs: Horses become ataxic (incoordination), inability to empty bladder, and weakness of the tail. Some horses will become completely paralyzed; the prognosis for these horses is poor. In a small number of cases, horses can show abnormal mentation and develop cranial nerve signs. Most horses become mildly to moderately neurologic and stabilize rapidly. The neurologic signs can persist but most horses are normal by 3 to 6 months after onset of clinical signs.

Abortion: pregnant horses can experience spontaneous abortion between 7 days and several months after exposure. The mare will exhibit limited initial signs.


UPON onset of clinical signs (temperature), a nasal swab and a blood sample (purple top tube) should be performed. Nasal shedding can be of short duration.

At this time, the most rapid testing is by PCR.


The test is EHV-1/EHV-4 PCR

Send samples on ice packs (no wet ice!) to:

Livestock Disease Diagnostic Center 859-253-0571

1490 Bull Lea Road

P.O. Box 141125

Lexington, KY 40512-4125


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