Equine Herpesvirus-1 Myeloencephalopathy

Guidelines for management of the neurological form of EHV-1

  • Questions may be directed to Dr Malcolm C Roberts, NC State Veterinary Hospital (VH) 919-513-6630
  • Sources of information:
    • UC Davis Center for Equine Health
    • Equine Herpesvirus-1 Alert
    • USDA APHIS Center for Epidemiology and Animal Health
    • Equine Herpesvirus Myeloencephalopathy: A Potentially Emerging Disease
    • NCDA & CS
    • APHIS Veterinary Services Biosecurity – The Key to Keeping Your Horses Healthy
  • The primary objective of the policy guidelines is to raise the level of awareness and thus reduce the risk of interrupting equine service delivery at the VH and the Equine Health Center (EHC) at Southern Pines through quarantine resulting from admission, or development of a positive EHV-1 neurological case.
  • Upon taking a call for an appointment or emergency, the receptionist or house officer should:
    • Ask the owner/agent or referring veterinarian whether the horse has been at home or at a property within the past 30 days and has suffered from, or been in contact with another horse or horses exhibiting fever >102 Fahrenheit (>38.88 Celsius), plus signs of nasal discharge, coughing, and/or evidence of neurological dysfunction.
    • Advise the owner/agent that on arrival at the facility the horse must remain on the trailer.
  • The likelihood is that the horse with suspected exposure will be an otherwise healthy animal that is referred to the orthopedic, podiatry, outpatient radiology, elective soft tissue surgery, theriogenology, or ophthalmology services.
  • Although many medical cases are healthy, the probability is that there will be a more in depth history relating to the presenting problem, including the presence of fever and neurological dysfunction.
  • All horses presented to the VH or the EHC at Southern Pines (EHC) will have their temperature checked in the trailer before being unloaded, and subsequently will be walked in hand in a straight line and tight circled to assess the degree of coordination.
    • The owner/agent will be advised to take and record the horse’s temperature prior to loading the animal for transport to the VH or EHC, in case heat related stress occurs during transport in hot humid weather. The clinician will take this factor into account when deciding the horse’s disposition at the facility.
    • Applicable options if the horse’s temperature is >102º F (38.88ºC).
    • The horse’s presenting condition may be consistent with existing guidelines for isolation or restriction, and the horse will be placed in the appropriate location.
    • The horse can be admitted to the VH, to be housed in restriction in C-aisle north, effectively limiting although not precluding performance of the desired investigative or surgical procedure unless this is an ophthalmology emergency. The ophthalmology case will remain in restriction in C-aisle north for the entire period of hospitalization. It can be moved into isolation, or discharged.
    • The horse will not be admitted to the VH or EHC and should be returned home. The referring DVM will arrange for a reappointment when the horse has maintained a normal temperature and exhibited no other signs for at least 7 days.

Medical cases

  • A medical case with a fever and prior or current clinical signs or in contact history and any evidence of neurological disease must be examined by a clinician outside the hospital buildings prior to a decision on whether to admit the horse to restriction or isolation. Presence of these clinical signs may provide supportive evidence of exposure to or reactivation of EHV-1 virus with ensuing neurological signs.
  • If the horse is ambulant with signs suggestive of EHV-1, it will be admitted directly to isolation stall 7.  Isolation stalls 5 & 6 are backup options. Horses already in isolation stalls 5, 6, or 7 should be moved to isolation stalls 1-4.
  • Other horses with clinical signs suggestive of the neurological form of EHV-1 must be housed in isolation stalls 5 through 7. If these stalls are fully occupied by EHV-1 suspect or positive animals stalls 1-4 should be used.
  • If a case is EHV-1 positive on viral testing, quarantine for 21 days and retest using the same system. The isolation facility will be quarantined.
  • Length of quarantine is 21 days after the last clinical sign, which is usually temperature, and the horse is EHV-1 test negative (negative for EHV-1 shedding from nasal cavity and NO virus detected in blood).

Quarantine – confirmed cases

  • Once a positive horse is identified either voluntary or state quarantine should be imposed
  • Length of quarantine – 21 days after LAST clinical sign which is usually temperature
  • Expect quarantine to last 28 to 35 days
  • Discharge test requirements – negative for EHV-1 shedding from nasal cavity and NO virus detected in blood
  • The owner/agent of the EHV-1 suspect should receive advance notice that they will be required to sign a waiver at admission agreeing to their liability for all additional charges incurred at the VH (or EHC) if the facility is put under voluntary or state quarantine in the event that their horse is a positive EHV-1 neurological case. Quarantine for the admitted case can be expected to last 28 to 35 days. Charges will include required diagnostic testing.
  • The owners of other horses in isolation at the time that a suspect animal is confirmed to be EHV-1 positive will not be liable for the additional hospitalization charges incurred through the imposition of quarantine. However, they will be liable for the medical, supportive and level of care charges that would be incurred in the normal management of the problem necessitating admission to isolation.

Use of isolation

  • All standard isolation protocols apply with the below modifications
    • Any individual (students, clinicians, staff, etc.) that enters the stall or comes into contact with the patient will not re-enter the EFAVC main facility.  Treatment plans should be developed around this standard to facilitate major treatment times at shift change, so technical staff can leave immediately following treatments.
    • Any breach of protocol should be immediately reported to the attending clinician, the EFAVC Operations Manager, and the EFAVC Epidemiologist; quarantine of the potentially contaminated facility shall be implemented.

Diagnostic tests

  • Upon onset of clinical signs (temperature), a nasal swab and a blood sample (EDTA purple top tube) should be obtained. Nasal shedding can be of short duration. The most rapid testing is by PCR.
  • VH The virology laboratory (Dr Jim Guy, Ms Leah Scarborough, 513-6564) has the capability to determine the presence of EHV-1 from nasal swabs and blood samples.
  • Serum antibodies to EHV-1 can be determined in serum or CSF by indirect immunofluorescent antibody (IFA) within 24 hours. It is preferable for acute and convalescent sera to be assayed.
  • These diagnostic tests do not differentiate strains of the EHV-1 virus.
  • UC Davis has two laboratories capable of performing EHV-1 diagnostic tests including a real-time TaqMan® polymerase chain reaction assay (PCR) that will identify all strains of EHV-1 virus. Another RT-PCR assay has been developed to differentiate the neuropathic from the non-neuropathic EHV-1 virus. Currently this is part of a research study only.
  • on “Standard Submission Form”)
    • Lucy Whittier Molecular and Diagnostic Core Laboratory
    • Submission forms and information
  • Sample collection - submit nasal swabs dry and whole blood samples in EDTA tubes.
  • Results will be available by fax later in the day of receipt, or early the next day.
  • University of Kentucky Livestock Disease Diagnostic Center

Quarantine of the main hospital facility

  • The entire EFAVC facility will be quarantined in cases where a breach in isolation protocol is observed, the patient enters the main facility, or the state veterinarian suggests/institutes quarantine.
  • Quarantine time for all hospitalized patients is 14 days, following the last breach.
  • Attending clinicians are responsible for contacting owners to discuss the quarantine.
    • All communications should be recorded in the client communication log.
  • All patients in the quarantined facility will be handled with boots and gloves as standard ppe.


  • Real-time PCR results indicate the presence or absence of viral DNA in the specimens tested, but do not predict clinical outcome.
  • Molecular assays to differentiate between neurogenic and non-neurogenic strains have been developed and used for research purposes only. Additional validation will be necessary before use of these assays for diagnosis.
  • The interpretation of PCR viral detection for EHV-1 should be done only in the context of the presenting clinical signs for disease in the horse being tested.
  • The significance of a positive PCR in an asymptomatic horse is unknown.
  • Horses with high fevers and/or signs of coughing or mild nasal discharge, with or without neurological deficits should be tested for EHV-1 by PCR diagnostics if there are no other explanations for the signs of disease. Detection of a positive PCR for EHV-1 in such instances should warrant isolation and limited movement of exposed horses.