Viral encephalitis

What is viral encephalitis?

Encephalitis is the medical term for inflammation of the brain, a potentially life-threatening condition that can occur in people of all ages but which is fortunately very rare. It is caused by an infection with a virus. The course of viral encephalitis varies. Most people infected with viral encephalitis have only mild or no symptoms, and the illness doesn't last long. However, serious cases can have headache, high fever, lethargy, convulsions, delirium, coma, and or death. The survivors may have significant mental impairment, including loss of memory, inability to speak coherently, lack of muscle coordination, paralysis, hearing or vision defects.

Encephalitis can be of 2 types:

Primary
This form is due to a direct viral invasion of the brain and spinal cord. The virus can be sporadic or epidemic. The most common sporadic form, herpes simplex encephalitis, may start as a minor illness with headache and fever, followed by more serious symptoms. Epidemic varieties are commonly caused by mosquito-borne viruses. The major types of mosquito-borne encephalitis that infect people in the United States are eastern equine encephalitis, western equine encephalitis, St. Louis encephalitis, La Crosse encephalitis and, more recently, West Nile encephalitis.

Secondary (post-infectious)
This form follows or occurs with a viral infection in another part of the body such as chickenpox, measles (rubeola), mumps, rubella (German measles) or polio. The cause of encephalitis in some secondary cases may be a hypersensitivity reaction - an overreaction of the immune system to a foreign substance.

Primary encephalitis is the most serious kind of encephalitis, but the secondary form is more common. But because of the milder nature of secondary encephalitis, doctors see more cases of primary encephalitis.

What causes viral encephalitis?

Mosquitoes are responsible for the transmission of encephalitis from small creatures, usually birds and rodents, to humans. Birds who live near bodies of standing water, such as freshwater swamps, are susceptible to infection with an encephalitis virus. When a bird is infected with encephalitis, it carries high levels of the virus in its blood for a short time before recovering from the infection and developing immunity to the disease. If a mosquito feeds on an infected bird, the mosquito will become a lifelong carrier of the disease. The mosquito will transmit the infection to the next bird it feeds on, which will in turn give it to more mosquitoes. Usually, this transmission pattern cycles through without serious impact on either creature and without affecting humans. This is partly because mosquitoes' primary hosts are birds and small mammals, and they bite humans only as a second choice. However, sometimes environmental disasters, unusual weather or other climate changes cause an increase in the number of infected birds, as well as mosquitoes that feed on both birds and humans. Under these conditions, humans may be affected. The risk of occurrence is highest during the warm months when birds and mosquitoes are more in numbers.

What are the signs and symptoms of viral encephalitis?

These include:

• Drowsiness
  
• Confusion and disorientation
  
• Seizures
  
• Sudden high fever
  
• Severe headache
  
• Nausea and vomiting
  
• Tremor
  
• Bulging in the soft spots (fontanelles) of the skull, in infants
  Stiff neck.

Warning signs and symptoms include altered level of consciousness. In infants, the key symptoms are a stiff neck and a bulging in the soft spots of the skull (fontanelles). In older children, the initial symptoms may be a severe headache and sensitivity to light. In adults, mental disturbances may be more prominent as an initial symptom.

How is it diagnosed?

The clinical history and the physical examination provides a preliminary diagnosis which can be confirmed by:

1. Spinal tap (lumbar puncture): The most common way to diagnose encephalitis is to analyse the cerebrospinal fluid surrounding the brain and spinal cord. A needle inserted into the spine extracts a sample of fluid for laboratory analysis. Analysis of the fluid may reveal presence of an infection or an increased white blood count, a signal that the immune system is fighting an infection.
   
2. Electroencephalography (EEG): This procedure, which takes about half an hour, measures the waves of electrical activity produced by the brain. It's often used to diagnose and manage seizure disorders. Between 16 and 30 small electrodes are attached to the scalp with paste or an elastic cap. The brain is stimulated and the electrodes pick up the electrical impulses from the brain and send them to the EEG machine, which records the brain waves on a moving sheet of paper.
   
3. Brain imaging: A computerised tomography (CT) or magnetic resonance imaging (MRI) scan may reveal swelling of the brain.
   
4. Brain biopsy: Rarely, if diagnosis of encephalitis wasn't possible before death, using DNA methods or by CT or MRI scans, a small sample of brain tissue may be taken. This sample will be analysed in the laboratory to see if the virus is present.

What is the treatment?

Because viruses that cause encephalitis usually don't respond to antibiotics, treatment mainly consists of rest and a healthy diet including plenty of fluids to let the immune system fight the virus. In some cases, physical and speech therapy may be needed as part of treatment. To treat herpes simplex encephalitis, an antiviral agent such as acyclovir may be prescribed in the early stages of the illness. In some cases an anticonvulsant medication is prescribed. Anti-inflammatory drugs or medications that reduce pressure within the skull may also be used.

How can it be prevented?

Even though viral encephalitis is rare, a good way to prevent secondary encephalitis is to make sure you and your children are immunized against viral infections that may lead to encephalitis - chickenpox, measles (rubeola), mumps and rubella (German measles).

To prevent the breeding of mosquitoes:

• Repair all holes in doors and windows.
  
• Eliminate standing water by emptying buckets, scrap tires, drains, flowerpots and similar containers. Change your pet's water dish daily.
  
• Drain puddles when possible.
  
• Clean the gutters and drain flat roofs regularly.
  
• Empty unused swimming pools.

To protect yourself and your family against mosquito bites:

• Carefully apply mosquito repellent to skin and clothing. Mosquito repellent containing diethyl toluamide (DEET) is recommended as the most effective form of bite-preventive treatment. It has an excellent safety profile in adults, children and pregnant women.
  
• Always cover the arms and legs of children playing near swampy areas.
  
• Long trousers, long-sleeved clothing and socks thick enough to stop the mosquitoes bites are protective, and should be worn outside after sunset. However, it may be hard to follow such advice in a hot climate. Light colours are less attractive to mosquitoes.
  
• Sleep in rooms that are properly screened with gauze/screen/wire-mesh over the windows and doors. There should be no holes in the gauze/screen/wire-mesh and no unscreened entry points to the room. Air-conditioned rooms are good, too.
  
• Spray the room with an insecticide before entering to kill any mosquitoes that may have got inside during the day.
  
• Avoid unnecessary outdoor activity when mosquitoes are most prevalent, such as dawn, dusk and early evening. Mosquitoes bite particularly at twilight and at night, so you should take most precautions during this time.

Prognosis for severe encephalitis

Prognosis for severe encephalitis depends on a host of factors such as the following:

• The age of the patient (Worse outcomes can be anticipated for infants less than one year of age and adults over 55 years of age).
  
• Immune status.
  
• Preexisting neurological conditions.
  
• Virulence of the virus.