Murray Valley encephalitis
Murray Valley encephalitis (MVE) is a mosquito-borne viral disease of humans, affecting the central nervous system and able to cause death. It occurs naturally throughout the northern half of Australia, Papua New Guinea and eastern Indonesia.
MVE is caused by a Murray Valley encephalitis virus and was previously known as Australian encephalitis. It was first isolated from Culex annulirostris mosquitoes in 1960 and was shown to be a Group B arbovirus related to, but distinct from, Japanese encephalitis virus. MVE virus belongs to the Flaviviridae family of RNA viruses and is spread only by the bite of mosquito that is infected with a virus. Naturally MVE virus is carried mostly by water birds. Mosquitoes become infected by biting birds or other animals.
The Murray Valley encephalitis develops in about 5-15days after the bite of infected mosquito. Although the great majority of infected people will show no symptoms at all, around 20 percent of those who become sick (approximately on person in a thousand will develop disease symptoms), die and further 25 percent may develop major intellectual or neurological complications. Adults who have gown up in areas where MVE virus occurs in the wild are usually immune following infection during childhood.
Possible symptoms of MVE may include: fever, irritability, severe headache, neck stiffness, muscle tremors, confusion, vomiting, nausea, dizziness, lethargy etc. Patients with the severe form of Murray Valley encephalitis get worse very quickly with confusion and worsening headaches, increasing drowsiness and possible fits.
February to April (wet season rains) usually is the season of most risk of getting the Murray Valley encephalitis and the main areas of risk being the Kimberley and Pilbara regions in Western Australia. There have been seven major outbreaks of MVE in Australia since 1917. The last was in 1974 when 58 cases were reported from all mainland states. Since 1974 nearly all cases of MVE have occurred in north of Western Australia and the Northern Territory.
There is no vaccine to prevent Murray Valley encephalitis and there is no medical cure, so the best way of staying healthy is to avoid being bitten. Use of effective mosquito repellents, fly screens, mosquito bed nets or avoiding being outdoors during the dusk or dawn hours when mosquitoes are most active are possible ways of minimizing the risk of getting the MVE.