The AVA is sharing the below following information on 2 recent detections of EHV-1, as provided by Queensland Chief Veterinary Officer (CVO) Dr Fiona Thompson.
Veterinarians are advised to stay vigilant and up to date with biosecurity measures to prevent and manage equine herpesvirus type 1 (EHV-1) following two recent detections. EHV-1 was detected in one horse with neurological signs in the Townsville region and up to three horses with abortions on a single property in the Toowoomba region.
EHV-1 is a highly contagious viral disease of horses and in Australia commonly causes mild respiratory disease, occasionally causes abortion and very rarely, neurological signs. EHV-1 is endemic in Australia.
For all horses presenting with neurological and respiratory signs, it is essential that veterinarians consider the zoonotic risk and testing requirements for Hendra virus.
Clinical disease
EHV-1 (and EHV-4) infection in young horses usually presents as an acute febrile respiratory illness that can spread rapidly. Signs include:
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fever (39-40.5oC)
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conjunctivitis
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depression
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nasal discharge and a cough
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lack of appetite
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possible swelling of the lymph nodes around the throat.
Subclinical infections are common, even in young animals.
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 defaecating
- 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. 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.
How it is spread
This 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.
Although horses with latent infection do not show clinical signs and do not spread the infection to other horses, reactivation (recrudescence) of infections may occur with stress or immune system compromise, resulting in viral shedding from the upper respiratory tract. During this time, the virus can be spread to other horses.
Diagnosis
The disease presentation is not specific to EHV-1 and laboratory testing is required to diagnose infection with EHV-1. Tests that may be used include PCR, virus isolation, serology and histopathology. Appropriate specimens include nasal swabs, whole blood (EDTA tube) and serum (red top tube), and in the case of abortions, foetal and placental tissues. In horses with neurological signs, CSF (antemortem) or brain and spinal cord (post-mortem) should be submitted. Serology requires an acute and convalescent titre; ideally 2-4 weeks apart.
Random testing for EHV-1, particularly without the presence of clinical signs, is not advised. Only horses in the acute stage of clinical disease should be tested.
Confirmation of an EHV-1 diagnosis may be complicated as the horse may have been previously infected. If samples obtained initially do not provide the answer, follow-up serological testing may be useful and help eliminate other differential diagnoses.
Treatment
Horses with suspected or confirmed EHV-1 infection should be isolated immediately. Strict biosecurity and hygiene practices should be followed to prevent spread of infection. Owners of other horses that are at risk should be advised to closely monitor their animals.
There is no specific treatment for EHV-1 in horses, however supportive care should be provided according to the signs observed and advice from equine medicine specialists may be useful to manage neurological cases.
Reducing the ongoing risks of EHV-1 respiratory infections and abortions include vaccination, minimising stress (especially for pregnant mares) and isolation of new horses for at least 14 days.
EHV-1 Case Management
Horse owners and people that manage horses have a legal obligation (general biosecurity obligation) to take all reasonable and practical measures to prevent or minimise the effects of a biosecurity risk. This means that horse owners and veterinarians are legally required to reduce the risk of EHV-1 infection and limit the spread of the virus when dealing clinically affected horses and other possible carriers.
If EHV-1 infection linked to abortion or neurological signs is confirmed in a horse, Biosecurity Queensland will work with the animal owner and their veterinarian to manage the situation and provide advice on actions people can take to meet their general biosecurity obligation. These actions aim to limit the spread of EHV-1 and prevent disease transmission to other horses and include but are not limited to:
- Restricting the movement of infected animals, close contact animals and contaminated material from the property
- Decontaminating any potentially contaminated equipment or items.
- Isolating and segregating any infected animals or close contact animals on the property.
- Advising neighbours with horses that a case of EHV-1 infection has been confirmed.
- Monitoring the health of infected animals and close contact animals on the property.
People are not at risk of EHV-1 infection however, other diseases that are transmissible to people (such as Hendra virus) could present with similar disease signs.
Further information
The abortogenic and neurologic strains of EHV-1 are category 1 restricted matter under the Biosecurity Act 2014.
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.
For more information visit our webpage: Equine herpesvirus type 1 (EHV-1) | Business Queensland
EHV-1 Treatment Information for Practitioners
The information below has been provided by Dr Allison Stewart, Equine Medicine Specialist – School of Veterinary Science – University of Queensland.
There is no specific treatment for EHV-1 in horses, however supportive care should be provided according to the signs observed. Catheterisation of the bladder is required at least 3 times per day when a horse is dribbling urine to prevent detrusor muscle damage. If the horse is dysphagic, oral fluid therapy utilising an indwelling small oral feeding tube is more economic than intravenous fluid therapy. For prolonged dysphagia, gruel/fluid feeding via a stomach tube will be provide nutrition. Recumbent horses will require turning using ropes every few hours and benefit from the use of a hydraulic sling to aid in standing. Prevention and care of pressure sores is essential. Corticosteroids (ie 20-30 mg IV daily for ~3 days per 500 kg horse) has been recommended.
Most horses with equine Herpes virus myeloencephalitis that survive to discharge do recover. Common complications include pressure sores, eye trauma, and bacterial cystitis. In most cases referral to a hospital for intensive care is warranted for any severely ataxic or recumbent horse.