Equine Herpesvirus Type IV (EHV-4)

Test codes:
S0074 - Qualitative detection of Equine Herpesvirus Type IV by polymerase chain reaction
P0013 - Equine respiratory panel (includes EHV-4 and other pathogens)

Equine herpesvirus I (EHV-1) and EHV-4 comprise two genetically and antigenically distinct groups of viruses that can cause viral rhinopneumonitis in horses. Both viruses are ubiquitous in horse populations worldwide. Each produces an acute febrile respiratory disease on primary infection, characterized by rhinopharyngitis and tracheobronchitis. Outbreaks of respiratory disease occur annually among foals in areas with concentrated horse populations; elsewhere, episodes are sporadic. Most of these outbreaks in weanlings are caused by strains of EHV-4. The age, seasonal, and geographic distributions vary and probably are determined by immune status and concentration of horses. In individual horses, the outcome of exposure is determined by viral strain involved, immune status, pregnancy status, and possibly age. Infection of pregnant mares with EHV-4 strains rarely results in abortion.

The mechanisms of EHV-1 and EHV-4 infections are significantly different. EHV-4 infections are restricted to respiratory tract epithelium and associated lymph nodes, while EHV-1 strains have a predilection for vascular endothelium, especially in the nasal mucosa, lungs, adrenal, thyroid, and CNS. Of additional significance is the leukocyte-associated viremia that occurs in EHV-1 infections, which may result in abortion or neurologic disease.

Equine viral rhinopneumonitis cannot be clinically differentiated from equine influenza, equine viral arteritis, or certain other equine respiratory infections solely on the basis of clinical signs. Confirmation can be achieved by virus isolation, preferably from nasopharyngeal swabs and citrated blood samples taken very early in the course of the infection and by serologic testing of acute and convalescent sera. However, culture identification of the virus is slow and not very sensitive. Serological testing requires 3 to 4 weeks to complete. Molecular detection by PCR is the most sensitive and specific method of identifying EHV-4 infection (Varrasso et al., 2001).

Utilities:

• Confirm the disease causing agent
• Shorten the time required to confirm a clinical diagnosis of EHV-4 infection
• Ensure that horse populations are free of EHV-4
• Early prevention of spread of this virus
• Minimize personnel exposure to this virus
• Safety monitoring of biological products that derive from horses

References:
Varrasso, A., Dynon, K., Ficorilli, N., Hartley, C.A., Studdert, M.J. and Drummer, H.E. (2001) Identification of equine herpesviruses 1 and 4 by polymerase chain reaction. Aust. Vet. J. 79:563-569.

Specimen requirements: Nasopharyngeal swab, or 1 ml whole blood in EDTA (purple top) or ACD (yellow top) tube, or tissue, shipped overnight at room temperature; or tissue shipped frozen.

For specimen types other than those listed here, please call to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodology:
S0074 - Qualitative PCR
P0013 - Qualitative PCR, qualitative reverse transcription PCR and qualitative real time PCR

Normal range: Nondetected