Murray valley encephalitis (MVE) is an insect-borne viral disease caused by murray valley encephalitis virus (MVEV), an arbovirus in the family Flaviviridae. MVEV is endemic in Australia and causes encephalitis in both horses and humans. Sporadic cases tend to occur in conjunction with extreme weather events such as flooding. Serological surveillance of 997 horses on 333 properties in South Australia between April 2011 and July 2011 reported antibodies to MVEV in 8% of sampled horses.

Transmission
The primary vector involved in MVEV transmission is the mosquito Culex annulirostris, and the primary hosts are waterbirds.