Equine Herpesvirus Type III (EHV-3)

Test code: S0073

Test name: Qualitative detection of Equine Herpesvirus Type III by polymerase chain reaction

Equine herpesvirus type III (EHV-3) causes coital exanthema, a contagious genital infection (vulva in mares, penis and scrotum in stallions), spread venereally and characterized by numerous small blisters or spots, sometimes called ‘the pox’. The blisters burst and become secondarily infected by skin bacteria, then heal leaving white (de-pigmented) skin spots. The disease has no direct effect on the fertility of stallions or mares, but natural mating must be stopped to allow the disease to run its course (usually 10 days to 2 weeks to complete healing) and to prevent further spread of infection.

Equine coital exanthema is probably transmitted only in the acute phase of the disease; horses do not appear to shed the virus after lesions have healed. However, the existence of a carrier state is unclear; some believe that the scars that persist after healing can identify potential carriers, while others state that asymptomatic carriers have not been identified. Immunity is short-lived, but evidence from stallions shows that recurrence is not likely within a single breeding season.

This virus has one antigenic type but also has small and large plaque variants in tissue culture, indicating that variation may occur in the severity of field outbreaks. Although the primary route of transmission is venereal, outbreaks have been documented in which transmission occurred via contaminated supplies and instruments or by the use of a single glove for rectal examination of many mares. It is probably for this reason that EHV-3 has also been isolated from animals that have not been bred.

A tentative diagnosis can be based on clinical signs but must be confirmed by identifying (using electron microscopy) the virus in cells from the margin of ulcers. However, this electron microscopy technique to identify this virus is not very sensitive. Acute and convalescent samples for serum neutralization or complement fixation tests have been proposed as diagnostic tools for EHV-3 infection, but these tests must be interpreted carefully because EHV-1 and EHV-4 have also been isolated from genital lesions. Molecular detection of EHV-3 by PCR is the most sensitive, specific and accurate tool in assessing the infectivity of an affected horse (Dynon et al., 2001; Kleiboeker and Chapman, 2004).

Utilities:

• Confirm the disease causing agent
• Shorten the time required to confirm a clinical diagnosis of EHV-3 infection
• Ensure that horse populations are free of EHV-3
• Early prevention of spread of this virus
• Minimize personnel exposure to this virus
• Safety monitoring of biological products that derive from horses

References:
Dynon, K., Varrasso, A., Ficorilli, N., Holloway, S., Reubel, G., Li, F., Hartley, C., Studdert, M. and Drummer, H (2001) Identification of equine herpesvirus 3 (equine coital exanthema virus), equine gammaherpesviruses 2 and 5, equine adenoviruses 1 and 2, equine arteritis virus and equine rhinitis A virus by polymerase chain reaction. Aust. Vet. J. 79:695-702.
Kleiboeker, S.B. and Chapman, R.K. (2004) Detection of equine herpesvirus 3 in equine skin lesions by polymerase chain reaction. J. Vet. Diagn. Invest. 16:74-79.

Specimen requirements: 1 ml whole blood in EDTA (purple top) or ACD (yellow top) tube, or lesion swab 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: Qualitative PCR

Normal range: Nondetected