Although the term "encephalitis" literally means "inflammation of the brain," it usually refers to brain inflammation resulting from a viral infection. The severe and potentially life-threatening form of this disease is rare. Experts suspect that the actual incidence of encephalitis is probably much higher — but because most people have such mild signs or symptoms, many cases go unrecognized. Encephalitis occurs in two forms - a primary form and a secondary form. Primary encephalitis involves direct viral infection of your brain and spinal cord. In secondary encephalitis, a viral infection first occurs elsewhere in your body and then travels to your brain. Seeing your doctor and receiving timely treatment is important because the course of the encephalitis is unpredictable.
Complications of Encephalitis
Severe viral encephalitis can cause:
In those who've had severe encephalitis, some problems may last for a year or more, including:
Some complications may be permanent, such as memory loss, the inability to speak coherently, lack of muscle coordination, paralysis, or hearing or vision defects.
Causes of Encephalitis
The cause of encephalitis is most often a viral infection. Some examples include:
Arboviruses transmitted by mosquitoes, ticks and other insects
Rabies transmitted through animal bites
Encephalitis takes two forms, categorized by the two ways that viruses can infect your brain:
Primary encephalitis. This occurs when a virus directly invades your brain and spinal cord. It can happen to people at any time of the year (sporadic encephalitis), or it can be part of an outbreak (epidemic encephalitis).
Secondary (postinfectious) encephalitis. This form occurs when a virus first infects another part of your body and secondarily enters your brain.
Also, bacterial infections, such as Lyme disease, can sometimes lead to encephalitis, as can parasitic infections, such as toxoplasmosis, in people with weakened immune systems.
Signs & Symptoms of Encephalitis
Most people infected with viral encephalitis have only mild, often flu-like symptoms, and the illness usually doesn't last long. In some cases, people might not have any symptoms. Possible symptoms include:
More serious infections can cause:
Confusion and hallucinations
Loss of sensation or paralysis in certain areas
Loss of consciousness
Bulging in the soft spots (fontanels) of the skull in infants
Diagnosis of Encephalitis
Diagnosing encephalitis may involve:
Spinal tap (lumbar puncture). One common way to diagnose encephalitis is to analyze the cerebrospinal fluid surrounding your brain and spinal cord. A needle inserted into your lower spine (below the level of the spinal cord) extracts a sample of fluid for laboratory analysis, which may reveal the presence of an infection or an increased white blood count — a signal that your immune system is fighting an infection. Your cerebrospinal fluid may also be slightly bloody if hemorrhages have occurred. Diagnosis of herpes simplex encephalitis can be difficult, but advances in using sensitive DNA methods have allowed detection of the virus in spinal fluid.
Electroencephalography (EEG). This procedure measures the waves of electrical activity produced by your brain. It's often used to diagnose and manage seizure disorders. A number of small electrodes are attached to your scalp with paste or an elastic cap as you recline. You remain still during the test, but at times you may be asked to breathe deeply and steadily for several minutes or to stare at a patterned board. At times, a light may be flashed in your eyes. These actions are meant to stimulate your brain. The electrodes pick up the electrical impulses from your brain and send them to the EEG machine, which records your brain waves on a moving sheet of paper. An abnormal EEG result may suggest encephalitis, but a normal result does not rule out the disease.
Brain imaging. A computerized tomography (CT) or magnetic resonance imaging (MRI) scan may reveal swelling of your brain. Or it may reveal another condition with signs and symptoms that are similar to encephalitis, such as a concussion. If encephalitis is suspected, brain imaging is often done before a spinal tap to look for evidence of elevated intracranial pressure.
Brain biopsy. Very rarely, if diagnosis of herpes simplex encephalitis isn't possible using DNA methods or by CT or MRI scans, your doctor may take a small sample of your brain tissue. This sample is analyzed in the laboratory to see if the virus is present. Your doctor may also try treatment with antiviral medications before suggesting brain biopsy.
Blood testing. Your doctor can confirm the presence of West Nile virus in your body by drawing a sample of your blood for laboratory analysis. If you have West Nile virus, an analysis of your blood sample may show a rising level of an antibody to the virus, a positive DNA test for the virus or a positive culture of the virus.
Treatments of Encephalitis
Treatment for mild cases mainly consists of:
A healthy diet, including plenty of liquids
Using acetaminophen (Tylenol, others) to relieve headaches and fever
More serious cases of encephalitis can be difficult to treat because the viruses that cause the disease generally don't respond to medications. However, some viruses, particularly the herpes simplex virus and varicella-zoster virus, respond to antiviral drugs such as acyclovir (Zovirax). If you have one of these kinds of virus-induced encephalitis, your doctor will likely start treatment with acyclovir immediately. Another antiviral that's sometimes used is ganciclovir (Cytovene).
In addition to antiviral medications, your doctor may also treat you with:
Anti-inflammatory drugs, such as corticosteroids, to help reduce swelling and pressure within your skull
Anticonvulsant medications to stop or prevent seizures
After the illness, you may also need physical and speech therapy.
Prevention of Encephalitis
The best way to prevent viral encephalitis is to avoid the viruses that lead to this disease. That means taking steps to prevent genital herpes, for one. It also means making sure you and your children are immunized against viruses that can cause encephalitis, such as chickenpox, measles (rubeola), mumps and German measles (rubella).
To protect yourself and your family against mosquito-borne encephalitis during an outbreak of the disease:
Dress to protect yourself. Wear long-sleeved shirts and long pants if you're outside between dusk and dawn.
Apply mosquito repellent. The Environmental Protection Agency has found only two products — DEET and picaridin — to be effective at controlling insect bites. When you're going to be outdoors, especially at dawn and dusk when mosquitoes are more active, apply a product containing one of these ingredients to the outside of your clothing and to your exposed skin. Don't spray insect repellent on your face; spray it on your hands and then apply it to your face. Don't use DEET on the hands of young children because they may put their hands in their mouths or eyes. The American Academy of Pediatrics advises parents not to use insect repellents on infants younger than 2 months of age. Instead, cover your infant's stroller or playpen with mosquito netting when outside.
Avoid mosquitoes. Refrain from unnecessary activity in places where mosquitoes are most prevalent. Additionally, avoid being outdoors from dusk till dawn whenever possible — that's the time when mosquitoes are most active.
Keep mosquitoes out of your home. Repair holes in screens on doors and windows.
Get rid of water sources outside your home. Eliminate standing water in your yard, where mosquitoes can lay their eggs. Empty birdbaths, drains, wheelbarrows and flowerpots, and remove old tires and unused containers that might hold water. Drain puddles when possible. Clean your gutters and drain flat roofs regularly.
Take advantage of nature's mosquito-controlling creatures. Fill ornamental pools with mosquito-eating fish. Consider placing houses for other mosquito eaters, such as bats, in your yard.
Look for outdoor signs of viral disease. If you notice sick or dying birds, report your observations to your local health department.
A vaccine is available to protect horses from West Nile virus. No vaccine is available for humans, but researchers are working to develop one.
When to seek Medical Advice
See your doctor as soon as possible if you or your children experience signs and symptoms that suggest encephalitis, a disease that can be serious and life-threatening. Additionally, other potentially serious conditions can cause similar symptoms and also need to be considered.
Urgent signs and symptoms in children and adults may include:
Altered levels of consciousness or hallucinations
Muscle weakness or loss of feeling
In infants, the key signs that immediate medical care is necessary are: