The highly contagious viral disease equine herpesvirus type 1 (EHV-1) has been detected in up to three horses with abortions on a single property in the Toowoomba region.

In Australia, EHV-1 commonly causes mild respiratory disease, occasionally causes abortion and very rarely, neurological signs. EHV-1 is endemic in Australia.

Queensland Chief Veterinary Officer (CVO) Dr Fiona Thompson said EHV-1 (and EHV-4) infection in young horses usually presents as an acute febrile respiratory illness that can spread rapidly. Signs include:

• fever (39-40.5oC)
• conjunctivitis
• depression
• nasal discharge and a cough
• lack of appetite
• possible swelling of the lymph nodes around the throat

“Subclinical infections are common, even in young animals,” Dr Thompson said.

“After initial infection, the virus goes into a latent or dormant state, persisting at low levels in the white blood cells and the trigeminal ganglia neurons without causing clinical disease or spread of infection to other horses.

“Most adult horses have latent EHV infections.

“Less commonly, EHV-1 infection can cause both sporadic and epidemic abortion (abortion storms), neonatal deaths, as well as neurological disease.”

Horses with neurological disease caused by EHV-1 infection can show signs including:

• fever
• ataxia, weakness, trouble standing, dog sitting (rear limbs often more severely affected than forelimbs)
• difficulty urinating (urinary overflow, dripping urine)
• difficulty defecating
• decreased tail tone
• decreased perineal sensitivity
• rarely – extreme lethargy and a coma-like state

“Overseas there have been multiple EHV-1 neurological outbreaks causing significant impacts to the horse industry including numerous horse deaths, widespread cancellation of events and heightened biosecurity measures to contain the virus,” Dr Thompson said.

“It is vital that any cases where EHV-1 is detected in horses with neurological signs are managed with heightened biosecurity including isolation and management of fomites and human-assisted spread.

“Abortion in horses due to EHV-1 usually occurs between 8-10 months’ gestation and, occasionally, as early as 4-5 months’ gestation.

“Abortions occur anywhere from 10 days to 12 weeks after virus infection. The mare may not show signs of respiratory infection prior to aborting.”

Dr Thompson said the disease is highly contagious and spreads easily by direct horse-to-horse contact or by contaminated fomites such as equipment, e.g. feed and water buckets) and tack (e.g. halters and bridles)

“Infection of EHV-1 occurs mainly by inhalation, but also by mucosal contact with material contaminated by nasal discharge or aborted foetuses,” she said.

Horses with suspected or confirmed EHV-1 infection should be isolated immediately and strict biosecurity and hygiene practices should be followed to prevent spread of infection.

If you become aware of the presence of EHV-1, causing abortion or neurological disease in horses, you must report it as soon as practicable to Biosecurity Queensland on 13 25 23 or contact the Emergency Disease Hotline on 1800 675 888.

This article appeared in On Our Selection News, 14 August 2025.