Hendra virus in horses: signs, the vaccine, flying-fox risk and who to call

If you think your horse might have Hendra, call your vet now. Keep people and other animals away from the horse until your vet has seen it. This article is general information, not veterinary or medical advice. If you're worried a person has been exposed, see a doctor.

Hendra virus is rare, but it's one of the few horse diseases that can kill people. Queensland's disease guide puts it bluntly: about 80% of infected horses and 70% of infected people die [1]. Since the virus was first identified in Brisbane, seven people have caught it, all after heavy exposure to the blood or body fluids of an infected horse, and four of them died, the most recent in 2009 [6].

Every owner in flying-fox country should know the signs, the risk factors and the phone numbers before they need them.

Where Hendra occurs

Flying foxes (fruit bats) are the natural host. They carry the virus without getting sick [3]. Horse cases have only been found in Queensland and New South Wales so far, but Agriculture Victoria says every part of Australia where flying foxes and horses live side by side is considered at risk [7]. A second genotype of the virus (HeV-g2) was reported in 2021 in flying foxes from Victoria, South Australia and Western Australia, and a sick horse near Newcastle, NSW, in October 2021 is the most southern horse case to date [7].

Hendra hasn't been detected in a Victorian horse, but Agriculture Victoria still advises precautions wherever flying-fox populations are close to horses [7].

There's no safe season. Infections in horses have happened throughout the year, so Queensland advises taking precautions year-round [1].

Signs in horses

Hendra can look like a lot of other illnesses. Queensland says it should be considered in any sick horse when the cause is unknown, particularly when the horse goes downhill fast [1]. Signs that have been linked to cases include [1]:

• rapid onset of illness
• fever
• increased heart rate
• discomfort or shifting weight between legs
• depression
• rapid deterioration with breathing and/or nervous signs.

Breathing signs include difficult or rapid breathing, and nasal discharge at death that can start clear and become frothy, white or blood-stained [1].

Nervous signs include a wobbly gait, apparent loss of vision in one or both eyes, aimless walking in a dazed state, head tilting and circling, muscle twitching, urinary incontinence and being unable to get up [1].

Not every infected horse shows every sign [1]. NSW Health notes that infected horses can shed the virus for a few days before they look sick [8], which is why everyday hygiene around horses matters even when they seem well.

How horses catch it

Horses are thought to become infected by contact with material contaminated by infected flying-fox body fluids and excretions [1]. The virus has been found in flying-fox blood, urine, faeces, placental material, aborted foetuses and birthing fluids [3]. It can then spread from horse to horse through direct contact with body fluids, or on shared gear [2].

The good news: Hendra isn't very contagious. Queensland notes it's more likely to affect a single horse than several, and most paddock cases have involved one horse that died without its companions being infected [2]. But companion horses have occasionally caught it after close contact with the first horse [2].

Cut the flying-fox risk on your property

Flying foxes feed on flowering and fruiting trees. Queensland lists trees found on properties where horses have been infected, including fig trees (Moreton Bay figs among them), melaleucas and paperbarks, eucalypts, bottlebrushes, mandarin trees, climbing asparagus vine, Cocos palm and white cedar [3]. Mangoes, papaws and other soft or stone fruit, palms, lilly pillies and grevilleas may also attract them [3]. The list isn't complete, so walk your own paddocks and note what's flowering or fruiting.

Queensland's risk-reduction steps [2]:

• Move feed and water containers out from under trees, and under a shelter if you can.
• Take horses out of paddocks with trees that are flowering or fruiting and attracting flying foxes. Put them back only once the flowering or fruiting has finished and the flying foxes have gone.
• If you can't move them, fence off the area under those trees, and clean up fallen fruit before horses go back in.
• Try bringing horses in at dusk and overnight, when flying foxes are usually most active.

NSW Health also advises protecting horse feed from flying-fox contamination [8], and Queensland Health suggests keeping food and water covered [6].

Don't try to get rid of the bats. Culling colonies doesn't work because flying foxes keep moving between colonies, and they're a protected species [3]. Agriculture Victoria says destroying or relocating flying foxes is not an effective risk measure and is illegal [7].

The Hendra vaccine

A registered vaccine is available, and Queensland calls vaccination "the most effective way to help manage Hendra virus disease" [5]. It also protects the people who handle horses by reducing the risk of the virus passing to humans [5]. Key points:

• It contains no live virus, so neither you nor your horse can catch Hendra from it [5].
• It isn't compulsory in Queensland [5].
• No vaccine is 100% protective. If Hendra is ever suspected, use full precautions and PPE even with a vaccinated horse [5].
• Agriculture Victoria says laboratory studies show the vaccine is effective against the newer HeV-g2 genotype too [7].

On timing, sources differ, so ask your vet. Barwon Equine Hospital's protocol lists two doses 3–6 weeks apart followed by a 6-monthly booster, starting from 4 months of age in young horses [10]. Agriculture Victoria refers to annual boosters after the initial priming course [7]. Your vet will go by the current product label and your horse's risk. Our horse vaccination schedule puts Hendra alongside tetanus and strangles, and the care planner can remind you when a booster is due.

Health4Horses, run by the vaccine's maker, hosts a registry where you can look up a horse's Hendra vaccination status [11]. Keep the dates on your horse health record too.

If you suspect Hendra: what to do

1. Call your vet immediately [4]. Vets who suspect Hendra follow set procedures and will take samples for testing at a government laboratory. Queensland says initial results are usually available one working day after the lab receives the samples [4].

2. Isolate the horse. Keep it away from other horses, people and animals, including pets, until your vet gives you an opinion [2]. Queensland defines "close contact" as being within 5 metres of the horse without a barrier such as a full-height wall [2].

3. Keep your distance while you wait [4]:

• avoid close contact with the sick horse and any horses that have been near it
• feed and water from a distance if you need to
• watch from a distance and tell your vet straight away if any horse gets worse.

4. If you must get close, cover cuts with a waterproof dressing, put on all your PPE before you approach, take it off carefully without touching your face, and wash your hands with soap and water straight afterwards [2].

5. Handle healthy horses first and the sick horse last. Clean and disinfect anything that's touched its body fluids, including halters, lead ropes and twitches, before using it on another horse [2].

6. Stop all movement. Don't travel with, work on, or take a sick horse to other properties or events, and don't let visiting practitioners such as farriers work on it [2].

If the test is positive in Queensland, Biosecurity Queensland works with the owner and vet. Steps can include movement restrictions, testing of other animals including pets, and tracing horses that left the property in the previous few weeks [4]. In Victoria, the property would be quarantined until other horses are cleared; horses with current Hendra vaccination will usually still be allowed to move [7].

Who to call, by state

Your own vet comes first everywhere. Then:

Worried about people? Contact your GP, local hospital emergency department or public health unit if you think someone has been exposed [4]. In people, symptoms usually begin 5 to 21 days after contact with an infected horse, and can start with fever, cough, sore throat and headache [6].

Everyday hygiene that protects you

Because a horse can be infectious before it looks sick, Queensland Health recommends simple habits around all horses [6]:

• don't kiss horses on the muzzle
• wash your hands after contact, especially before eating or touching your face
• cover wounds with waterproof dressings
• wear PPE (gloves, mask, eye protection) if you might contact body fluids.

Queensland Health also notes that no one with lower-level contact such as grooming, feeding or patting has ever caught Hendra [6].

Quick checklist

• Vet's number and the EAD Hotline (1800 675 888) saved in your phone
• Flowering and fruiting trees in your paddocks identified
• Feed and water moved out from under trees
• A Hendra vaccination conversation with your vet, and boosters in the care planner
• A basic PPE kit and an isolation spot at least 5 m from other animals
• Find an equine vet near you before you need one

A sick horse that's going downhill fast, with no obvious cause, is a reason to ring the vet and keep everyone back. Don't wait to see if it improves.