Arboviral disease in horses
Arboviral diseases are diseases spread by biting insects and may affect many different species, including horses, water birds and on rare occasions, humans. Arboviral diseases associated with Murray Valley encephalitis (MVE) virus, West Nile virus (Kunjin strain) and Ross River virus are known to occur in Victoria.
As transmission relies on the bite of infected mosquitoes, humans are not at risk of infection from direct contact with infected animals.
Clinical signs in horses
In horses, infection with arboviral disease viruses will not always cause clinical disease, however in some cases animals may present with neurological or musculoskeletal signs such as:
The clinical signs of arboviral disease also mimic a number of other illnesses, including notifiable diseases such as Hendra. It is therefore important to get an accurate diagnosis and wear suitable personal protective equipment when sampling or handling horses displaying neurological signs.
All Hendra investigations must be reported to Agriculture Victoria on the Emergency Animal Disease Watch Hotline 1800 675 888.
Resources on the safe management of suspected Hendra virus cases are available from the Queensland Government.
History of outbreaks
Ross River virus (RRV), Murray Valley encephalitis virus (MVEV), and West Nile (Kunjin)virus (WNVKUN) are all known to exist in Australia.
RRV is found across Australia, and the flaviviruses, MVEV and KUNV are found in Northern Australia in the Northern Territory, Queensland and northern Western Australia.
Sporadic outbreaks of MVEV have been reported in southeast Australia following periods of high rainfall and flooding, such as occurred in 1974, 2011 and 2021.
RRV is the most common mosquito-borne human pathogen in Australia, and each year thousands of cases are reported through state health departments. Until the 2011 outbreaks, arboviruses were rarely diagnosed as the cause of disease in horses. Consequently, the prevalence of these viruses in horses was considered low.
Over the spring and summer of 2010 to 2011, and again in 2021-2022,the southeast of Australia experienced unusually wet weather and flooding resulting in increased mosquito and wild bird populations. These conditions resulted in increased occurence of arboviral disease in horses.
Disease prevention involves reducing contact with mosquitoes, though this can be very challenging in a stable or paddock environment. The following measures can be used:
- Remove sources of stagnant water such as old buckets, tubs and tyres to reduce breeding sites for mosquitoes.
- Use suitable repellents or protective coverings such as summer rugs or fly veils.
- Stable animals during peak periods of mosquito activity (during dusk and dawn).
- Use commercial mosquito traps.
West Nile (Kunjin) virus infection virus is a notifiable disease in Victoria. This means it's a legal requirement to report cases of WNV.
There is currently no legal requirement to report suspected or confirmed equine cases of MVEV or RRV because they are not notifiable diseases of horses in Victoria, however owners should discuss the health of their animals with their private vet and determine the cause of any neurological or musculoskeletal signs.
Subsidies may be available from Agriculture Victoria for arboviral disease investigations.
See SDI Program for more information.
For further information on arboviral diseases in animals, please contact the District Veterinary Officer or Animal Health Officer at your local Agriculture Victoria office or call the Customer Call Centre on 136 186.