Hendra Virus Information

What is Hendra virus?

Hendra virus is a zoonotic disease, which means it can be transmitted from animals to people. Hendra virus can cause disease in horses and humans. Since being discovered in 1994, it has caused the death of more than 70 horses. Sadly, it has also claimed the lives of 4 out of the 7 humans infected between 1994 and 2014. Of those who passed away due to the disease, 2 were veterinary surgeons and 1 was the partner of a veterinary surgeon who became infected after assisting in a veterinary procedure.

How is Hendra virus transmitted?

Flying foxes are a natural reservoir for Hendra virus, although interestingly they do not show any signs of illness when infected.  Hendra virus can be transmitted from flying fox to horse, horse to horse and horse to human.  There is currently no evidence that the virus can be transmitted from flying fox to human, human to horse or human to human.

The exact route of transmission is unknown, but it is thought that horses become infected by contacting or ingesting material contaminated by infected flying fox body fluids (including saliva) and excretions.  The virus can also potentially spread from horse to horse through direct contact with infectious body fluids, or through indirect contact via equipment contaminated with infectious body fluids.

The cases of Hendra virus infection in people occurred following exposure to respiratory secretions (e.g. mucus) and/or blood and other body fluids from an infected horse.

How to reduce the risk of horses becoming infected with Hendra virus

Since 2012, a vaccine has been available to prevent horses becoming infected with Hendra virus.  In our opinion, vaccination is the single most effective way of reducing the risk of Hendra virus infection in horses.  For more information on the vaccine, click here.

There are also various husbandry procedures horse owners should routinely practice to reduce the risk of their horses becoming infected with Hendra virus:

  • Remove horse feed and water containers from under trees.  If possible, place feed and water containers under a shelter.
  • Remove your horses from paddocks where flowering/fruiting trees may attract flying foxes. Return the horses only after the trees have stopped flowering/fruiting and the flying foxes have gone. If it is not possible or practical to remove the horse from the paddock, consider fencing (temporary or permanent) to restrict access to flowering or fruiting trees.  Before returning the horses, ensure all fruit debris under the trees has been removed.  If it is not possible to remove your horses from paddocks for long periods, try to temporarily remove your horses during times of peak flying fox activity (usually at dusk and during the night).
  • Clean and disinfect gear exposed to body fluids from horses before using it on another horse.  This includes items like halters, lead ropes and twitches.  We can supply appropriate cleaning agents that are viricidal (will kill Hendra virus).
  • When cleaning contaminated equipment, wear gloves, cover any cuts or grazes and wash your hands thoroughly afterwards.
  • If your horse becomes sick, isolate it from other horses, other animals and people until a veterinarian’s opinion is obtained.
  • Always handle healthy horses before handling sick horses.  Only handle sick horses after taking appropriate precautions (including wearing personal protective equipment).
  • Be responsible with respect to biosecurity: do not travel with, work on or take sick horses to other properties or equestrian events
  • Do not allow lay equine practitioners (dentists and farriers) to work on sick horses
  • Seek veterinary advice before bringing any sick horse onto your property
Signs of Hendra virus infection in horses

Hendra virus infection in horses can cause a broad range of clinical signs.  Hendra virus infection should be considered in any sick horse where the cause of illness is unknown, and particularly where there is rapid onset of illness, fever, increased heart rate and rapid deterioration.  Although many of the early cases showed respiratory and neurological signs, some more recent cases were characterised simply by inappetance, lethargy and rapid deterioration.

The following signs have been associated with Hendra virus cases, however not all of these will be seen in any one infected horse:

  • rapid onset of illness
  • increased body temperature (fever)
  • increased heart rate
  • discomfort/weight shifting between legs
  • depression
  • inappetance (not eating)
  • rapid deterioration with respiratory and/or neurological signs

Respiratory signs include respiratory distress, increased respiratory rate, nasal discharge (clear, frothy or bloody).  Neurological (nervous) signs may include a wobbly gait, apparent loss of vision, aimless walking in a dazed state, head tilting and walking in a circle, muscle twitching, urinary incontinence and an inability to rise.

If you suspect your horse may be infected with Hendra virus, avoid close contact with the horse and any other horses that may have had contact with it.  Isolate the sick horse (wearing personal protective equipment if possible).  Ensure children cannot have close contact with any potentially infected horses.  Seek veterinary advice (please see link to our current policy on attending unvaccinated horses).

Vaccinating your horse against Hendra virus

Since 2012, a vaccine that protects horses from Hendra virus has been available.  The vaccine works by stimulating the production of protective antibodies.  If a vaccinated horse is subsequently exposed to Hendra virus, the antibodies work by binding to the viral particles, preventing them from establishing an active infection in the horse.  No live virus is used at any stage during the manufacture of the vaccine, and it therefore cannot cause Hendra virus infections.  The vaccine is used as an aid to prevent clinical disease in horses caused by Hendra virus, and also to reduce viral shedding.  Reduction/prevention of viral shedding is extremely effective in preventing human infection.

Vaccination is the single most effective way of reducing the risk of Hendra virus infection in horses.  Vaccination is an important measure to prevent human infection and death, and therefore provides a public health and workplace health and safety benefit.  We regard the safety of our staff as an absolute priority.  As of May 31, 2017, our practice will not attend horses that are not up to date with the prescribed vaccination regime (refer to our link outlining in more detail our policy on unvaccinated horses). 

The current vaccine protocol is as follows:

  • an initial primary course of 2 vaccines, with an interval of 21-42 days between vaccines
  • a booster 6 months after the second primary vaccine
  • annual vaccine boosters thereafter

All vaccinated horses are required to be microchipped.  This allows vaccinated horses to be identified on the national Hendra vaccination database.  The vaccine is regarded as safe for pregnant mares, and is safe for foals over 4 months of age.

There has been much debate and social media discussion about the safety of the vaccine. We have assessed the relevant research into the Hendra virus vaccine and based on this research,  clinical trials and personal experience we strongly recommend the vaccine as a safe and effective prevention of Hendra virus in horses. 

Vaccination of horses is strongly encouraged.  However do not become complacent after your horses have been vaccinated.  Always practice good personal hygiene and sensible husbandry practices when working with horses, regardless of their vaccination status.

If you have any questions about Hendra virus in general, including vaccination protocols, please call us at any time.

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