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Diagnostic Laboratory Services

EHV Clearance for Equine Abortion EHV CLEARANCE FOR EQUINE ABORTION AND NEONATAL DEATH Introduction

We recommend that Equine Herpesvirus (EHV) clearance for animal movement on breeding farms following an abortion should be based on a three-stage testing procedure to avoid the risk of false positive or false negative results. This includes a gross post mortem examination with histological examination of fixed fetal and placental tissue sections and the EHV DNA PCR test.

If lesions appear equivocal, immunohistochemical staining for the EHV antigen may be required(usually approximately 5% of cases).

Clearance tests can be carried out on selected tissues sent to AHT following gross post mortem examination elsewhere (Option 1) or as part of a complete post mortem investigation carried out at AHT (Option 2).

Option 1: Postal Samples

Following a preliminary gross post mortem examination performed by the attending veterinary surgeon, appropriate tissues for herpesvirus diagnosis or clearance are: fetal liver, lung, spleen, adrenal gland and thymus. Pooled fresh tissue preferably in transport medium (or otherwise in a labelled sterile container) should be submitted for PCR and tissues fixed in 10% neutral buffered formalin (NBF) should be submitted for histopathological examinations. A second paired set of samples labelled from the chorion (cervical star, body and both horns) should also be submitted in transport medium for PCR and in NBF for histopathological examinations.

The cost for the combined PCR and histological testing is £80.00* and the usual turnaround time for both tests is up to 48 hours for samples received Monday to Thursday, and up to 72 hours for samples received at other times . Where the two tests give discrepant results (or only fixed tissue is received) the immunohistochemical stain will be performed within the total £80 charge, results take up to one week.

If on a budget an EHV PCR can be performed on its own using fresh tissues samples for £45.

Option 2: Post Mortem Examination Performed at AHT

The post mortem examination involves consideration of equine Herpesvirus status, as well as other potential causes of abortion or neonatal death. The placenta should always be submitted with the fetus where possible. The cost of the post mortem examination is £200.00* including laboratory and disposal charges. Turnaround time is as in option 1 above.

* Prices are valid from 1st October 2010 to 30th September 2011

All EHV-1 diagnoses are copied to the AHT epidemiology team, who are able to offer advice on further testing, isolation and movement of horses.

Further information can be found in the Horserace Betting Levy Board Code of Practice on Equine herpesvirus-1, which is available on request to Diagnostic Laboratory Services.

EQUINE ABORTION AND NEONATAL FOAL DEATH

Prompt diagnosis of any abortion or neonatal foal death is important in safeguarding the present and future reproductive health of the individual mare and, in the case of infectious abortions (such as EHV-1 or 'viral abortion') in reducing risk of further abortions or foal losses by in-contact mares. Because the major source of infection in cases of viral abortion is the aborted fetus, and to a lesser extent the fetal membranes and fluids, the aborting mare must be isolated from any other stock especially mares in late pregnancy until a diagnosis has been made. Meanwhile, movement of horses on and off the premises should be stopped.

Diagnosis of the cause of abortion is made by examination of the fetus and membranes, which should be sent to a veterinary pathology laboratory experienced in equine abortion and neonatal death investigations, carefully contained in a leak-proof bag, with the help and advice of the attending veterinary surgeon. The mare should be examined by a veterinary surgeon to check for any complications related to the abortion, such as retained placenta.

If it is not possible to send the whole fetus with placenta, or foal to the laboratory, samples of the following tissues should be collected to achieve rapid herpesvirus abortion clearance: pooled liver, lung, spleen, adrenal gland and thymus with placenta (cervical star, body and both horns in a separate tube.

Using microscopic examination of tissues collected from the fetus and placenta, in combination with the PCR test, which is sensitive enough to detect even minute quantities of viral DNA, it is usually possible to achieve a diagnosis of herpesvirus abortion within 48 to 72 hours.

If herpesvirus infection is confirmed, isolation, movement restrictions and strict hygiene procedures should be followed. These procedures are detailed in the Horserace Betting Levy Board (HBLB) Code of Practice for Equine herpesvirus (EHV). Copies of the code may be requested from the HBLB (telephone 020 7333 0043), and are available on the Board's website: www.hblb.org.uk or from Diagnostic Services at AHT.

The Animal Health Trust operates a 7 day-a-week abortion screening service using the procedures outlined above, and can be contacted by the stud veterinary surgeon in the event of an abortion. Directions to the Animal Health Trust can be found on our website www.aht.org.uk.