Murray Valley encephalitis virus (MVEV) is a zoonotic flavivirus endemic to northern Australia and Papua New Guinea. It is the causal agent of Murray Valley encephalitis (MVE; previously known as Australian encephalitis or Australian X disease). In humans, it can cause permanent neurological disease or death. MVEV is related to Kunjin virus, which has a similar ecology, but a lower morbidity rate. Although the arbovirus is endemic to Northern Australia, it has occasionally spread to the southern states during times of heavy rainfall during the summer monsoon season via seasonal flooding of the Murray-Darling River system. These outbreaks can be "...decades apart, with no or very few cases identified in between".