What Is Encephalitis? What Causes Encephalitis?

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Main Category: Neurology / Neuroscience
Also Included In: Infectious Diseases / Bacteria / Viruses
Article Date: 28 Oct 2009 - 4:00 PST

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Encephalitis is inflammation of the brain resulting from a viral infection. Encephalitis usually begins with flu-like symptoms, such as fever and headache. The symptoms rapidly worsen, and may cause seizures, changes in mental state, such as confusion, drowsiness and loss of consciousness, or a coma.

The severe and potentially life-threatening form of this disease is rare.

According to Medilexicon's medical dictionary, encephalitis means "inflammation of the brain."

Encephalitis occurs in two forms:

• Primary form. Primary encephalitis involves direct viral infection of the brain and spinal cord.


• Secondary form. In secondary encephalitis, a viral infection first occurs elsewhere in the body and then travels to the brain.

Seeking immediate medical assistance and receiving timely treatment is important because the course of the encephalitis is unpredictable. A person with encephalitis can suffer life-threatening damage to their brain. The damage caused to the brain can result in long-term complications, such as memory loss, epilepsy, and personality and behavioral changes.

Encephalitis can occur in people of any age, although children under seven and adults over 55 are more vulnerable to infection.

In recent years improvements in diagnosing techniques and the introduction of new anti-viral medicines (such as acyclovir) have significantly improved survival rates for encephalitis.

There are several vaccinations that protect against some of the viruses that can cause encephalitis.

The mumps, measles and rubella (MMR) vaccine is the best way to protect children from encephalitis. Before the introduction of the MMR vaccine, measles used to be one of the leading causes of encephalitis in children.

What are the signs and symptoms of encephalitis?

A symptom is something the patient reports and feels, while a sign is something other people, including a doctor may detect. For example, a headache may be a symptom, while a rash may be a sign.

Usually, encephalitis begins with flu-like symptoms, such as a headache and a general sense of feeling unwell. Most people infected with viral encephalitis have only mild symptoms and the illness typically does not last long. In some cases, individuals might not have any symptoms. Possible symptoms include:

• fever
• headache
• irritability
• joint pain
• lethargy, sluggishness

If after a few hours or days, more serious symptoms follow. They may include:

• aversion to bright lights (photophobia)
• bulging in the soft spots (fontanels) of the skull in infants
• changes in mental state (such as confusion)
• confusion and hallucinations
• disorientation
• double vision
• drowsiness
• high temperature (fever) of 38ºC (100.4ºF) or above
• inability to control physical movements
• inability to speak
• loss of consciousness
• loss of sensation or paralysis in certain areas
• muscle weakness
• nausea
• rash
• seizures
• stiff neck
• tremors
• unusual behavior and personality changes (e.g. being suddenly aggressive)
• vomiting

Flu-like symptoms that rapidly get worse and change a person's mental state should be treated as a medical emergency.

Urgent signs and symptoms in children and adults may include:

• distorted levels of consciousness or hallucinations
• mental disturbances
• muscle weakness or loss of feeling
• seizures

In infants, the key signs that immediate medical care is necessary are:

• body stiffness
• bulging in the soft spots of the skull (fontanels)
• inconsolable crying
• vomiting

What are the causes of encephalitis?

There are two forms of Encephalitis:

• Primary encephalitis (Infectious) . This occurs when a virus directly invades the brain and spinal cord. Less commonly, infection can come from a bacteria or fungi. It can occur at any time of the year (sporadic encephalitis), or it can be part of an outbreak (epidemic encephalitis).


• Secondary (post-infectious) encephalitis. This form occurs when a virus first infects another part of the body and subsequently (secondarily) enters the brain. The immune system responds to a previous infection by mistakenly attacking the tissue of the brain.

Bacterial infections, such as Lyme disease can sometimes lead to encephalitis. Parasitic infections, such as toxoplasmosis can cause encephalitis in people with weakened immune systems.

Most often, the cause of encephalitis is a viral infection. Some examples include:

• Herpes viruses
• Arboviruses transmitted by mosquitoes, ticks and other insects
• Rabies transmitted through animal bites

Some of the more common causes of encephalitis:

Herpes viruses

These include:

• Herpes simplex virus. There are two types of herpes simplex virus (HSV) infections. HSV type 1 (HSV-1) more commonly causes cold sores or fever blisters around the mouth. Although very rare, it is the most important cause of fatal sporadic encephalitis. The HSV type 2 (HSV-2) more commonly causes genital herpes.


• Varicella-zoster virus. This virus is responsible for chickenpox and shingles. It can cause encephalitis in adults and children. However it tends to be mild.


• Epstein-Barr virus. This herpes virus causes infectious mononucleosis. If encephalitis develops, it is usually mild, but can be fatal in a small number of cases.

Childhood infections

In rare instances, secondary encephalitis occurs after vaccine-preventable childhood viral infections, including:

• German measles (rubella)
• Measles (rubeola)
• Mumps

In this case, encephalitis may be due to hypersensitivity or an overreaction of the immune system to a foreign substance.

Days or weeks after the initial infection has occurred, the immune system starts to produce infection-fighting antibodies that are meant to be used to fight the virus, but instead they are sent to the brain. This leads to inflammation of the brain's tissue. It is still unclear exactly why post-infectious encephalitis develops in certain individuals.

Arboviruses

Those viruses are transmitted by mosquitoes and ticks. Organisms that transmit disease from one animal host to another are called vectors. Mosquitoes are vectors for the transmission of encephalitis from small creatures (birds and rodents) to humans. This type of encephalitis is fairly uncommon.

In the United States, the following types of mosquito-borne encephalitis occur:

• Eastern equine encephalitis. Outbreaks occur most commonly in the eastern United States. This infection generally afflicts horses and birds. It can also affect humans, although fewer than 10 cases are reported in most years. Although some people experience it only as a mild illness, eastern equine encephalitis is fatal in about one-third of the cases. Symptoms of eastern equine encephalitis usually appear three to 10 days after a bite by an infected mosquito.


• La Crosse encephalitis. Named for La Crosse, Wis., where the virus was first recognized in 1963. Unlike other forms of viral encephalitis, this virus is passed to mosquitoes from chipmunks and squirrels. It usually affects children and is rarely fatal. Symptoms appear five to 15 days after a bite by an infected mosquito.


• St. Louis encephalitis. This virus is transmitted to mosquitoes by birds. The mosquito vector breeds in areas of standing water, including polluted pools, roadside ditches and containers such as birdbaths, flowerpots and discarded tires. Symptoms appear within a week to 10 days. The mortality rate can be as high as 30 percent for this type of encephalitis. Older adults have a higher mortality rate.


• West Nile encephalitis. This virus first appeared in the United States in 1999 and spread across most of the country over the next several years. Birds are its main animal hosts. However, in rare cases, the disease can spread from person to person through organ transplant, blood transfusions or breast-feeding, or from mother to unborn child. Symptoms are generally mild, but the disease can be severe, especially in older adults and those with weakened immune systems. Symptoms appear within five to 15 days of being bitten by an infected mosquito.


• Western equine encephalitis. Most reports of western equine encephalitis come from the central and western Plains of the United States. This infection affects horses and, rarely, humans. It flourishes in birds that live near irrigated fields and farming areas. Symptoms appear between five and 10 days after a bite. It is less likely to be fatal, but can result in brain damage and other major complications, particularly in infants.

Usually, the brain is protected from viral infections by the blood-brain barrier. It is a thick membrane that filters out impurities from blood before allowing it to enter the brain.

However, in a small number people, often for reasons that are unclear, the infection can break the blood-brain barrier and infect the tissue of the brain.

Once a virus has bypassed the blood-brain barrier, it enters brain cells and damages them. This leads to a loss of normal brain function. If left untreated, encephalitis can result in coma and eventually death.

What are the risk factors of encephalitis?

A risk factor is something which raises the likelihood of developing a disease or condition. For example, obesity increases the risk of developing diabetes type 2; therefore, obesity is a risk factor for diabetes.

Anyone can develop viral encephalitis. But some factors put you at greater risk:

• Age. Some types of encephalitis are more prevalent or more severe in young children or older adults.


• Geographic regions. Visiting or living in areas of the country where mosquito-borne viruses are common increases the risk of epidemic encephalitis.


• Outdoor activities. People with outdoor jobs, hobbies such as gardening, jogging, golfing or bird-watching… should be extra careful during an encephalitis outbreak.


• Season of the year. The warm months are the prime mating time for birds and mosquitoes.


• Weakened immune system. Individuals with an immune deficiency (resulting from instance from of AIDS or HIV, cancer therapies or organ transplantation) are more susceptible to encephalitis.

How is encephalitis diagnosed?

Diagnosing encephalitis may involve:

• Spinal tap (lumbar puncture). Encephalitis can be diagnosed by analyzing the cerebrospinal fluid (CSF) surrounding the brain and spinal cord. A needle inserted into the lower spine extracts a sample of fluid for laboratory analysis.
  
  The CSF is subjected to a series of tests that can help to confirm a diagnosis of encephalitis. The tests range from a simple white blood cell count to more complex tests, such as polymerase chain reaction (PCR).
  
  PCR is a recent innovation that has been very useful in helping to confirm diagnoses of encephalitis. It involves taking small samples of genetic material and cloning it in order to build up a more detailed genetic picture. It enables quick identification of the virus responsible for encephalitis.


• Electroencephalography (EEG). This procedure measures the waves of electrical activity produced by the brain. A number of small electrodes are attached to the scalp with paste or an elastic cap. 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. 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 the brain. If encephalitis is suspected, brain imaging is often done before a spinal tap to look for evidence of elevated intracranial pressure. CT scans help detect changes in the structure of the brain, such as inflammation, while ruling out other possible causes of the symptoms, such as a stroke, brain tumor or aneurysm.


• Brain biopsy. Very rarely, if diagnosis of herpes simplex encephalitis is not possible using DNA methods or by CT or MRI scans. A small sample of the brain tissue is taken. This sample is analyzed in the laboratory to see if the virus is present. Treatment with antiviral medications may be tried before suggesting brain biopsy.


• Blood testing. In order to confirm the presence of West Nile virus in the body.

Getting a prompt and accurate diagnosis in suspected cases of encephalitis is essential. It is very important to rule out other possible causes of the symptoms, such as meningitis or stroke, which require different treatments to encephalitis.

What is the treatment of encephalitis?

Treatment for mild cases mainly consists of:

• Rest
• A healthy diet, including plenty of liquids
• Using acetaminophen (Tylenol, others) to relieve headaches and fever

Treatment in more severe cases:

There are three central aims in the treatment of encephalitis which are:

• Stopping and reversing the process of infection, using anti-viral medication or other appropriate medication.


• Controlling any immediate complication of encephalitis, such as seizures or dehydration, caused by fever.


• Preventing long-term complications such as memory loss or epilepsy.

Most people being treated for encephalitis will be admitted to an intensive care unit (ICU). An oxygen mask will be used to help with breathing, and feeding tubes will provide nutrition and keep the body well hydrated.

Acyclovir

A medicine called acyclovir (Zovirax) has proved to be very effective in treating cases of encephalitis that has been caused by the herpes virus. It stops the virus from reproducing and spreading further into the brain.

The earlier acyclovir is used in cases of encephalitis, the lower the risk of long-term complications. Therefore, treatment with acyclovir is usually started before all the diagnostic tests are complete. If tests reveal that the encephalitis has a different cause, such as bacteria, then acyclovir will be substituted with an appropriate medication. Acyclovir is given by injection (intravenously), usually three times a day for 14-21 days.

Common side effects of acyclovir include:

• diarrhea
• headache
• nausea
• vomiting

Less common side effects include:

• Liver damage
• Hallucinations
• Decrease in the amount of white blood cells produced by the bone marrow. This can augment vulnerability to infection.

Another antiviral that is sometimes used is ganciclovir (Cytovene).

Corticosteroids

Corticosteroids are used in cases of post-infectious encephalitis because they momentarily stop the immune system from working (immunosuppressant). As a result it reduces any inflammation in the brain and prevents further damage.

Sedatives

In the case of repeated seizures due to encephalitis, sedatives such as benzodiazepine can be used to prevent further seizures.

After the illness, in some cases physical and speech therapy may be needed.

What are the complications of encephalitis?

Around two-thirds of people who have had encephalitis will develop one or more long-term complications as a result of underlying brain damage.

Individuals who have had severe encephalitis may have some problems lasting for a year or more, including:

• depression
• epilepsy
• fatigue
• memory problems
• personality and behavioral changes
• personality changes
• problems with speech and language
• walking problems
• weakness

Some severe complications may be permanent, such as memory loss, the inability to speak coherently, lack of muscle coordination, paralysis, hearing or vision defects.

Severe viral encephalitis can cause:

• seizures
• respiratory arrest
• coma
• death

Risk factors that increase the probability of someone experiencing a long-term complication include:

• being above 60 years of age
• having symptoms of coma when getting to hospital
• a delay between the onset of symptoms and the beginning of treatment

Due to the various possible complications, recovery from encephalitis may be assisted with several specialized services including:

• occupational therapists
• physiotherapy
• psychologists
• speech and language therapists

Before discharge from hospital, a full assessment of the patient's health and social care needs should be carried out.

Memory problems

Memory problems are particularly widespread in people who have had encephalitis that is caused by the herpes simplex virus. This is because the virus is known to damage the temporal lobes, which is the part of the brain that is responsible for forming new memories and storing old ones.

The damage causes two types of memory problems:

• problems remembering new information
• problems recalling events before the onset of the illness

Memory loss is rarely total, and most people will be able to remember family members and friends. However, they may be unable to recall specific events.

Previously learnt skills, such as typing or swimming, are usually unaffected. There may be some problems in speaking, particularly remembering certain words.

Living with someone who has memory problems

There are several practical steps:

• Displaying photographs of family and friends in prominent places and labeling them with their names.


• Encouraging the person to keep a diary and write notes.


• Having a regular routine.


• Keeping the home environment well structured and organized. Keeping things in the same place as much as possible.


• Putting signs in places where a person with memory problems may not remember something, such as a note at the door that reminds them what not to forget.


• Using a wall chart that displays the date and any events that are taking place during the day.

Personality and behavioral changes

People who experience brain damage as a result of encephalitis often have problems reading the facial emotions of other people. As a result, they often misjudge how people are feeling. On occasion, this can make them appear insensitive or rude.

Some other common emotional and behavioral changes are:

• Mood swings. There is a loss of emotional control. The person can react strongly or unpredictably to apparently trivial events and situations. They may also experience rapid swings in their mood.


• Frustration and anger. Many people become frustrated at the loss of their normal capabilities. This frustration can occasionally cause feelings of bitterness and resentment.


• Anxiety. Some people may experience an overwhelming sense of anxiety because they are aware of the changes in their behavior. It can lead to an obsessive fear.


• Depression. It is common, once the person realizes that fully recovering will not be possible.

How can encephalitis be prevented?

MMR vaccine. The most effective way to protect a child against encephalitis is to make sure that they are given the measles, mumps and rubella (MMR) vaccine.

The first MMR vaccination should be given to all children at around 13 months of age. A booster dose is given before they start school (when they are between 3 and 5 years of age). Between 5 to10% of children are not fully immune after the first dose, therefore the booster jab increases protection and results in less than 1% residual risk.

Other vaccinations. Vaccinations are also available for two types of encephalitis that are spread by insects:

• Japanese encephalitis. It is a type of viral encephalitis that is spread by mosquitoes. The condition has been almost eliminated in Japan due to immunization. It is widespread in parts of Asia, particularly in rural areas. A vaccination against Japanese encephalitis is recommended before travelling extensively or working in areas where Japanese encephalitis is widespread.


• Tick-borne encephalitis. It is a type of viral encephalitis that can be transmitted to humans by the bite of an infected tick or, less commonly, drinking unpasteurized milk from infected animals (particularly goats). Tick-borne encephalitis occurs in Central and Eastern Europe. A vaccination against tick-borne encephalitis is recommended for people who intend to hike, camp or work in rural areas where infected ticks may be present.


• West Nile virus. A vaccine is available to protect horses but no vaccine is available for humans. Researchers are currently working to develop one.

To protect yourself and your family against mosquito-borne encephalitis during an outbreak of the disease:

• Apply mosquito repellent. The Environmental Protection Agency has found only two products (DEET and picaridin) to be effective at controlling insect bites. Mosquitoes are especially active at dawn and dusk. Apply a product containing one of these ingredients to the outside of clothing and to exposed skin.
  
  Do not spray insect repellent directly onto face; spray it first on the hands and then apply it to the face. Do not 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 widespread. Avoid being outdoors from dusk till dawn whenever possible.


• Keep mosquitoes out of your home. Repair holes in screens on doors and windows.


• Protective dressing. Wear long-sleeved shirts and long pants when outside between dusk and dawn.


• Eliminate standing water. This is where mosquitoes can lay their eggs. Empty birdbaths, drains, wheelbarrows and flowerpots. Remove old tires and unused containers that might hold water. Drain puddles when possible.


• Nature's mosquito-controlling creatures. Fill ornamental pools with mosquito-eating fish. Bats also are mosquito eaters.


• Outdoor signs of viral disease. Sick or dying birds should be reported to the local health department.

Written by Stephanie Brunner B.A.


Copyright: Medical News Today
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