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Murray Valley Encephalitis - A Rare Viral Infection

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Murray Valley encephalitis (MVE) is a rare condition caused by the Murray Valley encephalitis virus. It causes acute and severe illnesses in humans and can be fatal.

Medically reviewed by

Dr. Abhishek Juneja

Published At May 16, 2023
Reviewed AtFebruary 6, 2024

What Is Murray Valley Encephalitis?

The Murray Valley encephalitis virus (MVEV) is a virus that belongs to the Japanese encephalitis serogroup. This virus is endemic to New Guinea and Australia. From the early twentieth century through 1974, it also caused the outbreak of encephalitis in New South Wales' east coast of Australia. The virus cycles between Ades and Culex mosquito species and large water birds. It spreads to man by infected mosquito bites. The highest outbreaks occur in the month of summer following heavy rains, that is, from February to July.

How Does Murray Valley Encephalitis Spread?

Murray Valley encephalitis spreads to humans through a mosquito bite. It is a nocturnal mosquito active in the early evening and pre-dawn. This mosquito breeds in freshwater wetlands and pools throughout Australia. The virus enters the mosquitoes when they bite the birds like herons or egrets which are water-living birds. This illness does not transmit from one person to another person. This condition is not transmitted by coming into contact with some other birds or animals. Individuals who spend their time outside for their work or who live near river regions are more susceptible to this kind of illness.

What Are the Signs and Symptoms of Murray Valley Encephalitis?

The people with Murray Valley encephalitis have no symptoms, but some might have mild symptoms that include:

More severe symptoms include:

  • Fever.

  • Confusion.

  • Nausea.

  • Vomiting.

  • Neck stiffness.

  • Seizures.

  • Shaking.

  • Headache.

  • Muscle tremors.

  • Drowsiness.

These neurological features progress in different clinical courses. They are:

  • It can progress to parkinsonism, stupor, progressive motor decline to death.

  • Brainstem and cranial nerve involvement with tremors.

  • Prominent spinal cord involvement.

  • Encephalitis followed by recovery.

The intubation period varies from five to 15 days. The symptoms appear eight to ten days after the bite. There is no evidence of person-to-person transmission.

What Are the Radiographic Features of Murray Valley Encephalitis?

Asymmetrical early bilateral thalami involvement and further extension into the brain stem is classical regardless of MRI imaging or brain stem. Less commonly, cervical and temporal lobes may also be involved depending upon the clinical course.

  • CT (Computed Tomography) - The lesions on CT are hypodense and involve thalami extending down to the brain stem with the progression of the disease. The lesions may exert a mass effect and cause obstructive hydrocephalus.

  • MRI (Magnetic Resonance Imaging) - The most striking feature of MRI includes symmetric high T2-weighted signal intensities that affect thalami bilaterally and extend down into the brainstem.

What Is the Recovery Time?

The recovery time of Murray Valley encephalitis depends upon the severity of the disease. In mild cases, the patient starts to improve within a few days. People with more severe symptoms take several days to months to recover and might need speech therapy, physiotherapy, and other forms of rehabilitation. Some people will be left with brain damage and paralysis, while some will not survive.

Who Is at Risk for Murray Valley Encephalitis?

The people traveling to New Guinea, southeastern Australia, and remote northwestern Australia are at risk of being infected with Murray Valley encephalitis. There are a few activities that can increase the traveler's chance of being infected. They are as follows:

  • Spending time outdoors.

  • Traveling during summer, especially when mosquitoes are more common.

What Is the Differential Diagnosis of Murray Valley Encephalitis?

The differential diagnosis of Murray Valley encephalitis includes:

  • Toxic leukoencephalopathy (an unsafe substance-induced encephalopathy damaging cerebral white matter).

  • Eastern equine encephalitis (a rare and dangerous virus that spreads over the eastern and Gulf Coast regions by mosquitoes).

  • Japanese encephalitis.

  • West Nile fever (a West Nile virus infection, usually transmitted by mosquitoes).

  • St. Louis encephalitis (a condition brought on by the Saint Louis encephalitis virus, which is spread by mosquitoes).

  • Flavivirus encephalitis.

How Is Murray Valley Encephalitis Treated?

The healthcare provider may diagnose the infection with a blood test and lumbar puncture to test the sample of the fluid around the spinal cord. No specific antiviral therapy is available for Murray Valley encephalitis. Hence, supportive management like corticosteroids and antiepileptics is encouraged. Mortality is reported between 15 to 30 percent, and about 15 to 30 percent of patients have long-term neurological complications.

How Can Travelers Prevent Murray Valley Encephalitis?

There are no medications or vaccines available that prevent Murray Valley encephalitis. However, the following measures can be taken by travelers to protect themselves.

  • Use an EPA-Registered Insect Repellent - The EPA-registered insect repellents are proven effective and safe. They are proven safe for breastfeeding and pregnant women. Even if one uses sunscreen, apply insect repellent after sunscreen. Always dress the child in clothing covering the legs and arms, baby carriers, and strollers with mosquito netting. Always follow the label instructions, and do not use products containing para-menthane-dio or lemon eucalyptus oil on children under three years old. Do not apply insect repellent on the children's eyes, mouth, cuts, hands, or irritated skin.

  • Wear Long Pants and Long-Sleeved Shirts - Permethrin is an insecticide that kills mosquitoes. Use 0.5 percent Permethrin to treat clothes, gear, pants, boots, socks, and tents. Do not use it directly on the skin. The clothes treated with Permethrin provide protection even after multiple washing.

  • Try Sleeping Under a Mosquito Net - Try to sleep under a mosquito net while outside, as the mosquitoes live indoors and can bite during the day and at night. Permethrin-treated mosquito net provides more protection as compared to regular mosquito nets. Buy a mosquito net before traveling overseas.

  • Keep Mosquitoes Out of the Hotel Room or Home - Try to choose a lodging or hotel room with air conditioning or windows.

  • Avoid Stagnant Water: Prevent the stagnation of water near a home or campsite because it may serve as a breeding ground for mosquitoes. Refrain from staying outdoors for a much longer time.

  • Be Cautious While Applying Repellants to Babies: Repellants may need to be applied to a baby's clothing rather than their skin. Repellant should not be used on a newborn's or young child's hands.

Conclusion:

The best way to prevent Murray Valley encephalitis is to avoid being bitten by insects like mosquitoes and midges. Cover up as much as possible. The bite of an infected mosquito transmits Murray Valley encephalitis (MVE), and there is no specific treatment for MVE. However, the treatment involves supportive care.

Dr. Abhishek Juneja
Dr. Abhishek Juneja

Neurology

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murray valley encephalitisencephalitis
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