Mosquito-borne viruses in horses

There are 2 types of mosquito-borne viruses namely arboviruses and flaviviruses.


Alphaviruses include Ross River virus (RRV) which can cause disease and death. Clinical signs in horses of Ross River virus include:

  • fever
  • reduced appetite
  • muscular soreness
  • reluctance to move
  • sometimes swollen joints and glands.


Flaviviruses can infect the brain and nervous system of horses and humans. Most flaviviruses are exotic to Australia, however, Kunjin virus and Murray Valley Encephalitis (MVE) occurs in Australia and has caused deaths of horses and humans. Although most horses infected with flaviviruses remain clinically well, others may develop abnormalities of the brain and spinal cord. Clinical signs can include:

  • changes in behaviour
  • facial paralysis
  • difficulty swallowing
  • ataxia (wobbliness)
  • blindness
  • inability to rise.


Mosquito control is extremely important in helping to prevent arboviruses and flaviviruses. You can achieve mosquito control by:

  • regularly applying insect repellents
  • rugging horses
  • stabling horses at dusk and dawn to decrease mosquito bites during the most active periods.

Stable fans will reduce mosquito numbers by circulating the air, as mosquitoes prefer still air. Clear stagnant water from around stables and paddocks. If water sources contain a large number of mosquito larvae, consider stocking with fish that feed on such larvae or applying biological and or chemical control measures.

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