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, Kunjin virus and Ross River virus have been detected 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 staggering, incoordination, weakness and depression.
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 Kunjin virus (KUNV) are all know 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 and 2011.
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 2010-11 the southeast of Australia experienced unusually wet weather and flooding resulting in increased mosquito and wild bird populations. These conditions are thought to have initiated an outbreak of arboviral disease in horses.
Seasonal conditions in Victoria during the winter and spring of 2016 are again favourable for increased mosquito activity and potentially increases in arboviral disease, so horse owners are asked to be vigilant.
Avoiding contact with mosquitoes can be very challenging in a stable or paddock environment. The following measures may assist:
- Remove sources of stagnant water such as old buckets, tubs, tyres, etc. to reduce breeding sites for mosquitoes.
- Use suitable repellents or protective coverings such as summer rugs/fly veils.
- Stable animals during peak periods of mosquito activity (i.e. during dusk and dawn).
- Use commercial mosquito traps.
There is currently no legal requirement to report suspected or confirmed equine cases of MVEV, RRV or KUNV because they are not notifiable diseases of horses in Victoria, however owners should discuss the health of their animals with their private veterinarian and determine the cause of any neurological or musculoskeletal signs.
Enhanced Surveillance for Equine Arbovirus Disease Project
In response to flooding across Victoria in 2016, the Department of Health and Human Services (DHHS) have provided funding for the investigation of clinical signs typical of mosquito-borne arboviral infection in Victorian horses.
To monitor the incidence of cases of possible arboviral infection as a result of this event, and in support of DHHS's efforts to monitor arbovirus disease in humans, Agriculture Victoria is encouraging private veterinarians to assess and sample Victorian horses with signs typical of clinical arboviral infection.
The same process that is applied in the current Significant Disease Investigation (SDI) program will be used in this project (i.e. private veterinarians will be financially supported to undertake examination and sample collection, once the investigation has been approved by local Agriculture Victoria animal health staff).
Veterinarians will be reimbursed up to $400 per horse examined and sampled/resampled.
Note: the typical RODE form and AgriBio submission form have been altered for this project.
For more information and copies of the forms follow the links below.
Visit the Health Vic – Murray Valley Encephalitis page.
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.