Causes

Primary encephalitis occurs when the virus directly invades your brain and spinal cord. The herpes simplex virus, which also causes cold sores and genital herpes, can cause this type of encephalitis.

You can also get primary encephalitis if you are bitten by a mosquito carrying the virus. Mosquitoes carry the virus after biting infected birds or small animals. You cannot get the virus directly from birds, animals, or other people.

Birds living near bodies of standing water are most likely to be infected with encephalitis. People usually are only affected if certain unusual environmental conditions cause an increase in the number of infected birds and mosquitoes. The risk of encephalitis is highest during warm months, when birds and mosquitoes reproduce.

Secondary encephalitis is a form of encephalitis that occurs during or after a viral infection in another part of your body, such as chickenpox, measles, mumps, and rubella. It may be caused by an overreaction of the immune system.

Symptoms

In mild cases, there may be no symptoms other than fever and headache. In more severe infections, symptoms may include:

• Sudden fever
• Headache
• Stiff neck
• Confusion
• Drowsiness
• Nausea and vomiting

Symptoms that require emergency treatment include loss of consciousness, seizures, sudden severe dementia, and poor responsiveness.

In infants, key symptoms are a stiff neck and bulging in the soft spots of the skull. Older children may have a severe headache and sensitivity to light.

Treatment

Treatment usually focuses on resting, eating well, and getting plenty of fluids to help your immune system fight the virus. Antiviral medications may be prescribed in the early stages of the illness. Several different types of medication may be prescribed to treat symptoms, such as:

• Anticonvulsants to prevent or treat seizures
• Corticosteroids to reduce brain swelling and inflammation
• Sedatives for irritability or restlessness

Over-the-counter medications may also be used for fever and headache. In severe cases, physical and speech therapy may be needed.

Prevention

You can protect your family against mosquito-borne encephalitis by taking steps to reduce your chances of being bitten by mosquitoes:

• Wear long sleeves and pants if you’re outside between dusk and dawn.
• Apply mosquito repellent that contains DEET to your skin and clothing.
• Eliminate standing water in your yard (such as in birdbaths, buckets, and puddles) and clean your gutters regularly.
• Repair holes in screens on windows and doors.

To prevent secondary encephalitis, make sure you and your family are immunized against the viral infections that can lead to encephalitis—chickenpox, measles, mumps, and rubella.