Japanese encephalitis in horses

Japanese encephalitis is a mosquito-borne viral disease that can cause reproductive losses in pigs  and encephalitis in other susceptible animal species. Horses are a susceptible species. It is caused by Japanese encephalitis virus which is a member of the Flavivirus genus.

The virus is primarily spread by mosquitoes feeding on infected animals and does not usually spread directly from animal to animal (i.e. it is not considered contagious). Whilst horses can become infected and occasionally show symptoms, they cannot infect mosquitoes and therefore cannot infect any other animals or humans. Certain types of mosquitoes can become infected with JE such as Culex sp. and these tend to most active at dawn and dusk.

Animals with the infection do not transmit the infection to other animals but may infect mosquitoes if bitten while they still have the virus in their blood. However, Horses do not gain enough virus to infect mosquitoes so are called an end host.

In general, spread is through the movement of the primary hosts of waterfowl, and waders such as herons and egrets, and through the movement of infected mosquitoes, often over long distances due to wind dispersal.

Clinical signs of Japanese encephalitis in horses

In horses many cases are asymptomatic and most clinical disease is mild, however more severe encephalitis can occur which may be fatal. Signs include:

  • fever
  • jaundice
  • lethargy
  • anorexia and neurological signs which vary with severity of the clinical disease.

Neurological signs can include in coordination, difficulty swallowing, impaired vision, and rarely a hyperexcitable form occurs. Disease has also been reported in donkeys.

I suspect Japanese encephalitis in my horse

Japanese encephalitis is a notifiable exotic disease in Victoria. If you suspect Japanese encephalitis your horse, immediately contact your local Agriculture Victoria staff or phone the all-hours Emergency Animal Disease Watch Hotline 1800 675 888.

Learn about the investigation procedure for diagnosis of Japanese encephalitis in horses.

Reducing the risk of infection

Japanese encephalitis virus is spread primarily by mosquitoes.

Integrated mosquito management is critical to reducing the risk to both people and animals. This includes controlling mosquitoes in various ways, such as reducing opportunities for breeding and attacking both the larval and adult life stages.

Chemicals for mosquito control

Chemicals used for larvae or adult mosquito control or used as a direct application to horses as a repellent

  • should be used in accordance with the product label
  • must be used only by people authorised to use chemicals
  • should be restricted to being applied only to areas required to be treated e.g. mosquito harbouring or breeding sites.

Chemical users must also keep records of their chemical use in accordance with relevant Victorian law.Horse owners should seek the advice of a veterinarian before applying chemicals to horses and must not apply chemicals in an off-label manner (i.e. a manner that is not consistent with the label instructions) to horses without the authorisation of a veterinarian.

Some repellents registered for use on horses do not allow treated horses to ever be used for human consumption.  These products must not be used if there is any likelihood the horse may enter the food chain at some time in the future.

Management practices

The virus can also be spread through management practices such as reuse of needles. To minimise the risk of spreading the virus through management practices avoid reusing needles between animals when injecting and thoroughly wash and decontaminate other equipment between animals.

Stable horses between dusk and dawn

If available, stabling horses between dusk and dawn will help, as the mosquito most likely to carry diseases of concern is a night-time feeder that stays outdoors. If stabling horses, consider using the following measures:

  • installing appropriate physical barriers at entry and exit points, e.g. a double door entry-exit system
  • turning off lights inside stables during the night
  • using fluorescent lights in stables that do not attract mosquitoes
  • placing incandescent bulbs around the stable perimeter to attract mosquitoes away from horses
  • screening building openings e.g. windows with shade cloth mesh that have been treated with an insecticide registered for treatment of that shade cloth material. Reapply product weekly by applying the chemical to screens as per the label instructions.
  • fogging, fans and automatic overhead misting systems to eliminate mosquitoes within stables
  • spraying of stable walls with insecticides registered for use as a structural treatment around agricultural buildings.  In order to prevent possible adverse reactions DO NOT apply to areas where horses may come into direct contact with the sprayed area.

In addition to stabling horses overnight there are other techniques to prevent mosquito bites. They include:

  • topical treatment of horses using chemicals registered for direct application to horses as mosquito repellents physical barriers - rugging and hooding horses in lightweight permethrin treated material (if climatically appropriate). Horse owners can treat their own horse rugs using agricultural chemicals registered for the treatment of horse rugs.
  • where possible reducing mosquito breeding sites on the premises such as dripping or leaking taps and water troughs, as well as discarding old tires which are a common breeding ground.
  • where it is not possible to fully eliminate all potential breeding sites, treat the breeding sites with an appropriately registered larvacide.
  • treating all interiors of horse vehicles with an aerosol insecticide registered for the control of mosquitoes.

Treatments for horses

There is no specific treatment for JE in horses; your veterinarian will provide supportive care according to the signs observed.

You are not at risk of JE infection from your horse; however, other diseases that are transmissible to people (such as Hendra virus in areas where flying foxes occur) could present with similar disease signs. Horses can be dangerous to people if they are unsteady on their feet so these risks should be kept in mind.

Horses are not a significant host of JE virus in terms of disease transmission, so there is generally no requirement for official controls to be put in place such as quarantine.

If your horse becomes infected, you may be at risk of being infected by mosquitoes in the area and should take precautions to avoid being bitten.

Vaccines

Vaccines for horses and pigs are used in some countries where the disease is endemic. No vaccines for animals are currently registered for general use in Australia. Expanded availability of animal vaccines is under consideration by the Australian Government Department of Agriculture, Water and Environment.

Horse movements

Movement controls are only needed for animals that contribute to disease transmission (primarily pigs).

Horses are not a significant host in terms of disease transmission, so there is generally no requirement for official controls on horses to be put in place such as quarantine and movement controls. People movements are not affected.

Horse events

Horses are considered an incidental host of the virus, so there is no need to prevent horse movements or congregations at events from a disease control perspective.

Event organisers are encouraged to disseminate human health and animal health messaging and advice on protection from mosquito bites before an events.

For events in proximity to active mosquito breeding grounds, organisers should consider seeking professional advice regarding integrated mosquito management options.

Human symptoms of Japanese encephalitis

A small number of people infected with JE virus may become seriously ill with encephalitis (inflammation of the brain). Other people may develop an illness with fevers, headaches and aches and pains.

Symptoms of encephalitis may include rapid onset of fever, headache, sensitivity to light, neck stiffness, vomiting, confusion or disorientation and sometimes seizures, progressing to coma. Anyone experiencing symptoms, particularly if they’ve visited regions near the border of Victoria and New South Wales or been in contact with pigs or with mosquitoes should seek urgent medical attention.

Any person who is experiencing any of the symptoms should seek urgent medical attention.

Please visit the Department of Health website for public health advice.


Fact sheets

Fact sheet: Information for horse owners

Download a copy of this fact sheet for printing:

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Japanese encephalitis (JE) is a mosquito-borne viral disease that can cause reproductive losses in pigs and encephalitis in horses. It is caused by the Japanese encephalitis virus which is a member of the Flavivirus genus.

The JE virus is primarily spread by mosquitoes feeding on infected pigs or birds and does not usually spread directly from animal to animal (i.e. it is not contagious from animal to animal, animal to human or human to human). Certain types of mosquitoes can become infected with JE virus such as Culex spp. and these tend to most active at dawn and dusk.

Pigs with the infection do not transmit the infection to other animals but may infect mosquitoes if bitten while they still have the virus in their blood.

Other livestock such as horses, cattle, sheep and goats are end hosts and cannot transmit the disease back to mosquitoes.

In general, spread is through the movement of waterbirds (herons and egrets) and through the movement of infected mosquitoes, often over long distances due to wind dispersal.

In horses many cases are asymptomatic and most clinical disease is mild, however more severe encephalitis (inflammation of the brain) can occur which can be fatal. Signs include fever, jaundice, lethargy, anorexia and neurological signs which vary with severity of the clinical disease. Neurological signs can include incoordination, difficulty swallowing, impaired vision, and rarely a hyperexcitable form occurs. Disease can also occur in donkeys. Infected horses cannot infect mosquitos.

There is no specific treatment for JE in horses; your veterinarian will provide supportive care according to the signs observed.

You are not at risk of JE infection from your horse; however, other diseases that are transmissible to people (such as Hendra virus in areas where flying foxes occur) could present with similar disease signs. Horses can be dangerous to people if they are unsteady on their feet so these risks should be kept in mind.

Horses are not a significant host of JE virus in terms of disease transmission, so there is generally no requirement for official controls to be put in place such as quarantine.

If your horse becomes infected, you may be at risk of being infected by mosquitoes in the area and should take precautions to avoid being bitten.

More than 90 per cent of JE virus infections are asymptomatic (show no signs of disease). Less than one per cent of people infected with JE virus develop clinical disease. A small number of people infected with JE virus may become seriously ill with encephalitis (inflammation of the brain). Other people may develop an illness with fevers, headaches and aches and pains.

Symptoms of encephalitis may include rapid onset of fever, headache, sensitivity to light, neck stiffness, vomiting, confusion or disorientation and sometimes seizures, progressing to coma. Anyone experiencing symptoms, particularly if they’ve visited regions near the border of Victoria and New South Wales or been in contact with pigs or with mosquitoes should seek urgent medical attention.

Any person who is experiencing any of the symptoms should seek urgent medical attention. Please visit the Department of Health website for public health advice.

Mosquito management is critical to reducing the risk to both people and animals.

Chemicals used for larvae or adult mosquito control or used as a direct application to horses as a repellent:

  • should be used in accordance with the product label
  • must be used only by people authorised to use chemicals
  • should be restricted to being applied only to areas required to be treated, e.g. mosquito harbouring or breeding sites.

Chemical users must also keep records of their chemical use in accordance with Victorian law.

Horse owners should seek the advice of a veterinarian before applying chemicals to horses and must not apply chemicals in an off-label manner (i.e. a manner that is not consistent with the label instructions) to horses without the authorisation of a veterinarian.

Some repellents registered for use on horses do not allow treated horses to ever be used for human consumption.  These products must be avoided if there is any likelihood of this occurring at some time in the future.

If available, stable horses between dusk and dawn. If stabling, consider using the following measures:

  • install appropriate physical barriers at entry and exit points (e.g. a double door entry-exit system)
  • turn off lights inside stables during the night
  • use fluorescent lights in stables that do not attract mosquitoes
  • place incandescent bulbs around the stable perimeter to attract mosquitoes away from horses
  • screen building openings (e.g. windows) with shade cloth mesh that has been treated with an insecticide registered for the treatment of netting/mesh.

In addition to stabling horses overnight there are other ways to prevent mosquito bites including:

  • topical treatment using repellents registered for direct application to horses
    • NOTE: certain repellents cannot be used on horses that may be slaughtered for human consumption at any later date
  • physical barriers –  rugging and hooding horses in lightweight permethrin treated material (if climatically appropriate); Horse owners can treat their own horse rugs using agricultural chemicals registered for the treatment of horse rugs
  • spraying of stable walls with insecticides registered for use as a structural treatment around agricultural buildings;  In order to prevent possible adverse reactions DO NOT apply to areas where horses may come into direct contact with the sprayed area
  • where possible, eliminate all potential mosquito breeding sites on the premises, including dripping or leaking taps and water troughs, or if not possible to eliminate, treat potential breeding sites with a chemical registered for the control of mosquito larvae.

Further information on mosquito control in horses is available at agriculture.vic.gov.au/JE.

If you suspect Japanese encephalitis in any animal, phone the all-hours Emergency Animal Disease Watch Hotline 1800 675 888.

There are two ways to protect yourself and your family: avoiding mosquito bites and vaccination.

Steps to protect yourself and your family against mosquito-borne diseases include:

  • wearing long, loose fitting clothes outdoors.
  • using mosquito repellents containing picaridin or DEET on all exposed skin.
  • limiting outdoor activity if lots of mosquitoes are about.
  • using ‘knockdown’ fly sprays and plug-in repellent devices indoors.
  • using mosquito coils in small outdoor areas where you gather to sit or eat.
  • making sure your accommodation is mosquito-proof.
  • sleeping under mosquito nets treated with insecticides if you don’t have flywire screens on windows on your home or are sleeping in an untreated tent or out in the open.
  • making sure there is no stagnant water around your home.
  • remember, dusk and dawn is when most mosquitoes are more active but some will also bite during the day.

Further information can be found at Beat the Bite.

Any person who is experiencing any of the symptoms should seek urgent medical attention. Please visit the Department of Health website for public health advice.

Vaccines for horses and pigs are used in some countries where the disease is endemic. No vaccines for animals are currently registered for general use in Australia. Expanded availability of animal vaccines is under consideration by the Australian Government Department of Agriculture, Water and Environment.

Movement controls are only needed for animals that contribute to disease transmission (primarily pigs).

Horses are not a significant host in terms of disease transmission, so there is generally no requirement for official controls on horses to be put in place such as quarantine and movement controls. People movements are not affected.

Horses are considered an incidental host of the virus, so there is no need to prevent horse movements or congregations at events from a disease control perspective.

Event organisers are encouraged to disseminate human health and animal health messaging and advice on protection from mosquito bites  in advance of events.

For events in proximity to active mosquito breeding grounds, organisers should consider seeking professional advice regarding integrated mosquito management options.

Fact sheet: Protecting your horses from mosquito bites

Download a copy of this fact sheet for printing:

+ Expand all- Collapse all

Japanese encephalitis virus is spread primarily by mosquitoes. Integrated mosquito management is critical to reducing the risk to both people and animals. This includes controlling mosquitoes in various ways, such as reducing opportunities for breeding and attacking both the larval and adult life stages.

Stabling horses between dusk and dawn can help, as the mosquito most likely to carry diseases of concern is a nighttime feeder that stays outdoors.

If stabling horses, consider using the following measures:

  • installing appropriate physical barriers at entry and exit points, e.g. a double door entry-exit system
  • turning off lights inside stables during the night
  • using fluorescent lights that do not attract mosquitoes
  • placing incandescent bulbs outside the stable perimeter to draw mosquitoes away from horses
  • screening building openings e.g. cover windows with shade cloth mesh that has been treated with an insecticide registered for the control of mosquitoes such as cypermethrin. Reapply product weekly by applying the chemical to screens as per the instructions contained on the chemical label
  • fogging, fans and automatic overhead misting systems to eliminate mosquitoes within stables
  • spraying of stable walls with insecticides registered for use as a structural treatment around agricultural buildings. In order to prevent possible adverse reactions DO NOT apply to areas where horses may come into direct contact with the sprayed area.

Include the following:

  • topical treatment of horses using chemicals registered for direct application to horses as mosquito repellents
  • physical barriers - rugging and hooding horses in lightweight permethrin treated material (if climatically appropriate). Horse owners can treat their own horse rugs using agricultural chemicals registered for such use
  • where possible reducing mosquito breeding sites on the premises such as dripping or leaking taps and water troughs, as well as discarding old tyres which are a common breeding ground
  • where it is not possible to fully eliminate all potential breeding sites, treat the breeding sites with an appropriately registered larvacide
  • treating the inside of horse floats and trucks with an aerosol insecticide registered for the control of mosquitoes.

When using chemicals for control of larvae or adult mosquitoes, or for direct application to horses, the chemicals:

  • should be used in accordance with the product label
  • must only be used by people authorised to use chemicals
  • should only be applied to areas requiring treatment e.g. mosquito harbouring or breeding sites.

Chemical users must also keep records of their chemical use in accordance with relevant Victorian law.

Some repellents that are registered for use on horses do not allow treatment on animals destined for human consumption. These products must not be used if there is any chance of the horse entering the food chain.

The virus can also be spread through management practices such as reuse of needles. To minimise the risk avoid reusing needles between animals and thoroughly wash and decontaminate other equipment between animals.

For more information on mosquito borne diseases and livestock in Victoria, visit agriculture.vic.gov.au

For more information about how to protect your friends and family from mosquito bites, visit the Better Health Victoria website.

Page last updated: 28 Apr 2022