Equine Viral Arteritis

Also known as: EVA — Equine Arteritis Virus — EAV

Introduction

This is a notifiable disease of horses in the UK caused by Equine Arteritis Virus. The disease infects the nasopharynx after respiratory transmission, causing a multitude of respiratory signs. The disease can also be spread venereally. After this, the virus spread to lymphoid tissue leading to leukopenia and immunosuppression. Then it disseminates through the circulatory system causing medial necrosis of arteries and thus haemorrhages and abortions, as well as oedema. Many cases are subclinical and only antibody positive.

The disease is controlled virus in the UK but AI and breeding schemes presents a real risk.

Signalment

More common in thoroughbreds than other breeds of horse. Most commonly seen in stud stallions or in broodmares.

Clinical Signs

Respiratory signs often appear first and these include dyspnoea, coughing and increased respiratory rate. This can also lead to interstitial pneumonia. In foals, interstitial pneumonia is the most common cause of death related to this disease. Once circulatory dissemination has occurred, diarrhoea, colic and haemorrhage will follow. Abortions occur after 10-30 days in 50% of pregnant mares (as opposed to Equine Herpes, which shows late abortions). Oedema - particularly ocular oedema is frequently present, giving rise to "pink eye". There will also be a pyrexia, rashes, ocular and nasal discharge, swelling of legs or scrotum and stiffness of gait.

Stallions become intermittent or persistent shedders from accessory sex glands but may show no clinical signs.

Diagnosis

Clinical symptoms are the usual indicator of the disease, but these may be variable.

A PCR on semen or an ELISA for serum antibody can be used to gain a definitive diagnosis.

Control

Vaccines:

Stallions require live attenuated vaccine and mares require killed whole virus.

Seropositive stallions restricted from teasing, mating or AI unless PCR tested negative. Persistent shedders should be castrated and serology should be performed on imported horses. Mares are tested within 4 weeks of mating.

Clinical disease is NOTIFIABLE in the UK.

In an outbreak, isolate and restrict movement until antibody-negative for one month.

References

Mair, T., Love, S., Schumacher, J. and Watson, E. (1998) Equine Medicine, Surgery and Reproduction WB Saunders Company Ltd

Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial

Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) Equine Internal Medicine (Third Edition), Saunders

Reed, S.M, Bayly, W.M, Sellon, D.C. (2004) Equine Internal Medicine (Second Edition) Saunders

Robinson, N.E., Sprayberry, K.A. (2009) Current Therapy in Equine Medicine (Sixth Edition) Saunders Elsevier

Rose, R. J. and Hodgson, D. R. (2000) Manual of Equine Practice (Second Edition) Saunders