Symptoms
People of all ages can be affected by MVE.
After being exposed to the virus, it takes 1-4 weeks (usually 2 weeks) for symptoms to appear. The first signs usually include high fever (often over 40°C) and headache, lasting 2-5 days. These symptoms can be hard to tell apart from those of JE and Kunjin virus encephalitis, which also occurs in Australia. Other symptoms of MVE include nausea, vomiting, and muscle aches. Early on, neurological symptoms (affecting the brain and nerves) may appear, such as extreme tiredness (lethargy), irritability, and confusion. Seizures almost always occur in children and sometimes in adults. In severe cases, people may develop neck stiffness, sensitivity to bright light (photophobia), and may lose consciousness or fall into a coma.
Most people who get infected with the MVE virus do not show any symptoms. In fact, only around one in every 150-1000 infected people develop severe disease.
Diagnosis
Blood tests are the main way to confirm infection by the MVE virus. These tests look for antibodies that the body makes to fight the virus. These antibodies usually appear in the blood 4-9 days after symptoms start and can last for months. A lumbar puncture (sometimes called a spinal tap) and/or urine tests can also help diagnose MVE.
Brain scans can’t diagnose MVE but can help support the diagnosis. They can show signs of infection before blood test results are available and help rule out other conditions. MRI is the most sensitive type of scan and can show signs of infection within a week of developing symptoms.
Treatment
There is no specific cure for MVE. Treatment focuses on supporting the patient’s body while it fights the infection. It’s important to quickly move patients to hospitals with an intensive care unit (ICU). Finding new treatments is challenging because MVE cases are rare. While similar conditions have been studied more, like JE, effective treatments haven’t been found for them either.
Outcomes
MVE affects each person differently. Among those with severe disease, outcomes vary. About 15-30% of people with severe MVE die. Among survivors, 30-50% have lasting brain or nerve problems. Only about 40% of patients recover fully without long-term effects.
In milder cases, symptoms may just be fever and headache. This broad range of outcomes, from mild to severe, shows how unpredictable MVE can be.
Prevention
There is currently no vaccine available to prevent MVE virus infection.
The best prevention is to protect against mosquito bites by wearing long, light-coloured clothing and applying mosquito repellents containing picaridin or DEET to exposed skin. People who work, live or spend time outdoors in rural areas must be extra careful and try to limit outdoor activity at times when mosquitos are prevalent. It is also important to remove stagnant water where mosquitos can breed. Fitting homes with netting or screens can also help prevent contact with mosquitos.
Travellers visiting risk areas should protect against mosquito bites and avoid spending time outdoors between dusk and dawn when mosquitoes are most active. Risk areas include the Top End, Katherine, and Barkly regions in the Northern Territory of Australia; the Kimberley, Pilbara, Gascoyne, and Midwest regions of Western Australia; and riverine areas including the Murray River region in south-eastern Australia. Most cases occur between January and June.
By Prav Prathapan, Encephalitis International and reviewed by Dr Sarah McGuinness, Consultant Physician, Department of Infectious Diseases, Alfred Hospital (Travel Medicine Clinic) and Senior Research Fellow, Infectious Diseases Epidemiology Unit, School of Public Health and Preventive Medicine at Monash University, Australia
FS074V1 Murray Valley encephalitis
Page created: June 2024. Page updated: June 2024. Review date: June 2027
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