NAME: Murray Valley encephalitis
SYNONYM OR CROSS REFERENCE: MVE, Australian X disease, Australian encephalitis, mosquito-borne encephalitis, viral encephalitis, arbovirus
CHARACTERISTICS: This virus is part of the Flavivirus genus and is an enveloped, spherical, positive-strand RNA virus(1,2,3). It has an icosahedral nucleocapsid and is between 40-70 nm in diameter(3,4).
PATHOGENICITY/TOXICITY: Lasting usually 2 weeks, the disease is characterized by a rapid onset of 2-5 days of fever, headache, myalgia, malaise, anorexia and nausea before neurological complications occur(1,5,6). CNS complications involve the brain, brain stem and spinal cord and include photophobia, numbness, stiff neck, encephalitis, paralysis (including respiratory paralysis), meningismus, spastic quadriplegia, coma and seizures(1,3,5,6,7). The disease can be life threatening and is more severe and common in children and aboriginal populations(4). 20 % of patients die and 50 % are left with lasting psychological and neurological complications such as cerebellar and extrapyramidal movement disorders, and cranial palsies(1,3,6).
EPIDEMIOLOGY: The MVE virus is present in Australia and New Guinea. The last major outbreak occurred in Australia in 1974 (58 cases with 13 deaths)(1). From 2001- 2006, two clinical cases were reported each year in Australia; however, most cases are asymptomatic with one clinical case for every 500-1000 infections(1). The disease usually occurs from February to April(6).
INFECTIOUS DOSE: Unknown.
INCUBATION PERIOD: The incubation period is between 5 and 28 days(1).
COMMUNICABILITY: The virus is not directly transmitted from person-to-person and most arboviruses produce low levels of viraemia that are very hard to detect(3,9,10). In chickens viraemia can last between 12-48h(9).
RESERVOIR: Water birds such as herons and pelicans (particularly the night heron Nycticorax caledonicus ) are the main reservoir for this virus; however, cattle, horses, and feral pigs may also act as reservoirs(1,4,5,6,8).
ZOONOSIS: Yes, from infected animals via mosquitoes. Infected animals can carry the disease without any clinical manifestations and transmit it to mosquitoes during a blood meal(6).
DRUG SUSCEPTIBILITY: None known
SUSCEPTIBILITY TO DISINFECTANTS: Susceptible to 1 % sodium hypochlorite, 2 % glutaraldehyde, 4 % formaldehyde, 70 % ethanol or propanol, 2-5 % phenol compounds, 2 % peracetic acid, 0.16 % iodine and 3-6 % hydrogen peroxide(11).
PHYSICAL INACTIVATION: Inactivated by heat with a 50 % reduction in 10 min at 50o C and complete inactivation in 30 min at 56o C(5). The infectious agent can also be inactivated by UV and gamma irradiation(5,12).
SURVIVAL OUTSIDE HOST: Not known.
Note: All diagnostic methods are not necessarily available in all countries.
PROPHYLAXIS: Avoid mosquito bites and use insect repellent(7).
LABORATORY-ACQUIRED INFECTIONS: There have been 3 cases of laboratory- acquired infections reported by SALS(10).
SOURCES/SPECIMENS: Blood, urine, exudates and CSF contain the infectious agent(10).
SPECIAL HAZARDS: None.
RISK GROUP CLASSIFICATION: Risk group 3(13).
CONTAINMENT REQUIREMENTS: Containment Level 3 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, tissue cultures, animals, or arthropods.
PROTECTIVE CLOTHING: Personnel entering the laboratory should remove street clothing and jewellery, and change into dedicated laboratory clothing and shoes, or don full coverage protective clothing (i.e., completely covering all street clothing). Additional protection may be worn over laboratory clothing when infectious materials are directly handled, such as solid-front gowns with tight fitting wrists, gloves, and respiratory protection. Eye protection must be used where there is a known or potential risk of exposure to splashes(14).
OTHER PRECAUTIONS: All activities with infectious material should be conducted in a biological safety cabinet (BSC) or other appropriate primary containment device in combination with personal protective equipment. Centrifugation of infected materials must be carried out in closed containers placed in sealed safety cups, or in rotors that are loaded or unloaded in a biological safety cabinet. The use of needles, syringes, and other sharp objects should be strictly limited. Open wounds, cuts, scratches, and grazes should be covered with waterproof dressings. Additional precautions should be considered with work involving animals or large scale activities(14).
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up (30 min)(14).
DISPOSAL: Decontaminate all materials before disposal by steam sterilization or incineration(14).
STORAGE: The infectious agent should be stored in a sealed and identified container in a level 3 containment laboratory(14).
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: September 2010
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2010