Japanese encephalitis and horses - the latest update
Updated: Jul 29, 2022
A WARNING to safeguard horses against mosquito-borne diseases may seem out of place in the depths of winter but unusually wet conditions in parts of Australia have brought the biters out in force.
There have been anecdotal reports of mosquitos in flooded areas on the western outskirts of Brisbane being in such large numbers at dusk, residents have been forced to stay indoors.
The Department of Agriculture, Forestry and Fisheries (DAFF) has confirmed horse owners should remain on guard against a number of mosquito-borne diseases, particularly in northern Australia.
It says diseases currently circulating include Japanese encephalitis virus (JEV), Murray River encephalitis and West Nile Virus, known as flaviviruses.
All are carried by mosquitos and can infect people and animals.
In an update on JEV provided yesterday, a department spokesman said the virus - which had been detected at 80 piggeries across NSW, Victoria, Queensland and South Australia and claimed the lives of three people this year - appeared to be in hand but people were still urged to be vigilant.
“Many of these infected piggeries have now been assessed as resolved by state/territory animal health authorities,” he said.
“At this stage, no cases of JEV in horses have been definitively confirmed, although there have been several probable cases across affected jurisdictions. This reflects difficulty in achieving a definitive laboratory diagnosis in horses.
“JE detections may continue in northern areas as it is anticipated that mosquito vectors will persist for a greater proportion of the year.
“The species of mosquitos responsible for transmission of JEV are active in warmer weather, so it is not anticipated that the current flooding alone will increase risk of JE or other mosquito-borne disease, in southern Australia.”
The spokesman said results of laboratory testing to confirm JEV and other flavivirus such as Murray River encephalitis and West Nile Virus in horses can take a number of weeks to come through.
He said the three viruses all present with similar signs to JEV, so any neurological signs in horses need to be reported to a veterinarian or the Emergency Animal Disease Watch Hotline on 1800 675 888.
“Even if you’re not sure whether it is JEV, still make the phone call – a false report is the best-case scenario,” the spokesman said.
“In horses many cases are subclinical, meaning that they can be infected but show no signs of the disease. Most clinical disease is mild however, more severe encephalitis can occur which may be fatal.
“Signs include an elevated temperature, jaundice, lethargy, anorexia and neurological signs, which can vary in severity. Neurological signs can include incoordination, difficulty swallowing, impaired vision, and rarely excitement.”
Care and prevention
The department recommends horse owners put measures in place to prevent mosquitos biting their horses.
It says the Australian mosquito that transmits JEV feeds at night and is reluctant to enter dwellings, so stabling horses between dusk and dawn is beneficial.
Other protection measures – which are just as relevant for managing the separate class of alphaviruses that include Ross River virus – are to put a hooded rug on them, a fly mask, and if the horse allows, applying a safe insect repellent.
“Work is underway to develop specific advice for horse owners on how to manage mosquitos around horse facilities including in stables and equestrian venues,” the spokesman said.
“In the meantime, there is further advice on protecting stabled horses in the JEV AUSVETPLAN.
“Note that permethrin treated horse fabrics that are sold with claims of insect control are viewed as unregistered agricultural chemical products under current legislation. Their supply and use in Australia have not been approved at this time.”
The latest information about JEV in animals is updated at outbreak.gov.au
Click here to download the JE AUSVETPLAN.