Encephalitis is the abnormal swelling or inflammation of the brain. People with encephalitis usually experience mild symptoms, if any. However, encephalitis can be severe or even fatal in some circumstances. Children are among the populations most often affected by encephalitis.

Encephalitis is acquired by either direct introduction to the brain and spinal cord (primary encephalitis) or as a secondary effect of a separate virus or condition (secondary or post-infectious encephalitis) already present in the body. Although less common than secondary encephalitis, primary encephalitis tends to be more dangerous.

There are a number of causes, including viruses (e.g., herpes simplex virus type 1), or bites from infected mosquitoes or ticks (arthropod-borne encephalitis), bacteria, fungi, parasites and others.

Pain and discomfort (e.g., headache, neck or back stiffness) are common symptoms of encephalitis. However, the type and severity of symptoms can vary greatly among children. Symptoms of encephalitis can be much more difficult to detect in infants. However, there are some symptoms typically associated with encephalitis in younger children, including a stiff body, full or bulging “soft spot” (fontanel) on the head and continuous crying.

Methods for diagnosing encephalitis include blood testing, brain imaging, spinal tap (puncturing of the lumbar to remove fluid) and others. Depending on the severity of the disease in the child, treatment options may involve rest, physical therapy, speech therapy, antibiotics and anticonvulsant (seizure) medications.

Encephalitis is a very rare inflammation of the white and gray matter of the brain. While technically referring to any brain inflammation, the term encephalitis is most commonly used to describe inflammation caused by a viral infection.

Children are among the populations most affected by encephalitis. Children with encephalitis are likely to have problems with brain and spinal cord function. Changes in the child’s neurologic condition cause mental confusion, seizures and other symptoms.

Mosquito- and tick-borne viruses (arboviruses) play a significant role in the spread of encephalitis worldwide. Birds and other small mammals serve as hosts to the disease. A mosquito feeding on an infected bird becomes an encephalitis vector (carrier) for the remainder of its life. The virus is then passed by the mosquito to other animals it feeds on, which, in turn, infect other mosquitoes feeding on that animal.

Arboviruses are of growing concern in light of continued global population growth, concerns of bioterrorism, social and environmental instability in underdeveloped countries and regions as well as global warming.

Encephalitis is most hazardous to infants, the elderly, individuals with compromised or weakened immune systems (e.g., cancer or HIV/AIDS patients) or people who reside in areas with high mosquito populations. Although children younger than age 1 and adults over age 55 are at the greatest risk of death, encephalitis can be potentially severe or even fatal to people of all ages.

The viral infection can occur either directly in the brain and spinal cord (primary encephalitis) or spread to these areas from elsewhere in the body (secondary or post-infectious encephalitis). It is also possible, though uncommon, to contract encephalitis through other organisms, such as bacteria, fungi or parasites.

A swollen or irritated brain will not maintain normal blood flow, usually causing ailments such as fever, headache or confusion. Frequently, the root cause of encephalitis can also agitate or inflame frail tissue structures lining the brain and spinal cord (meninges). When the meninges become inflamed, this condition is known as meningitis. It is not uncommon for encephalitis and meningitis to occur simultaneously.

When encephalitis (inflammation of brain tissue) and meningitis (inflammation of the membranes lining the brain) occur in combination, the condition is called meningoencephalitis. It is not uncommon for untreated meningitis to cause encephalitis, because in a number of cases infection spreads from the meninges to the brain. When the spinal cord is also affected, the term encephalomyelitis may be used.

Encephalitis (inflammation of the brain) is generally divided into two categories: primary encephalitis, which occurs when a virus invades the central nervous system (brain and spinal cord) directly; and secondary (postinfectious) encephalitis, which occurs when a virus first infects another part of the body and later enters the brain.

In addition, encephalitis may be further classified according to its cause:

• Viral encephalitis. The most common form, caused by infection from a virus. For instance, herpes simplex virus type 1 is the most common cause of encephalitis in the United States.
  
  
• Arthropod-borne encephalitis. A type of viral encephalitis that occurs after being bitten by an infected arthropod (e.g., mosquito, tick). These are further categorized according to the type of organism and/or the geographic region (e.g., Japanese encephalitis) where the diseases are more common.
  
  
• Bacterial, parasitic or roundworm encephalitis. Rare forms caused by infection with (respectively) bacteria, parasites or roundworms (from exposure to animal feces). The length of time required for incubation of these forms of encephalitis in humans varies depending on the cause and severity.
  
  
• Acute disseminated encephalomyelitis (ADEM). Typically a disease of prepubescent children, ADEM is rare in people over the age of 12 years. Signs and symptoms of ADEM are similar to those of multiple sclerosis. However, ADEM is usually associated with preceding infectious illness or immunization.

Encephalitis may also be categorized according to where it occurs in the body (e.g., cortical encephalitis only affects the brain cortex) or by accompanying conditions (e.g., purulent encephalitis is inflammation accompanied by brain abscesses). Infantile arthritis (caused by arboviruses or the herpes virus) and encephalitis periaxialis (inflammation of the white matter of the cerebrum) usually affect infants and young children.

Anyone can develop encephalitis (inflammation of the brain), although it is highly unlikely. Age is a major risk factor for encephalitis, with the very young and the elderly being at particular risk. This is because these populations typically have developing or weaker immune systems than other people, leaving them more vulnerable to infection.

Other factors that increase the risk of encephalitis include:

• Immune system problems. People with relatively weak immune systems are at greater risk of contracting encephalitis than otherwise healthy individuals. These include people with HIV or AIDS, cancer and other conditions, as well as those taking medications to suppress the immune system (e.g., after an organ transplant).
  
  
• Exposure to metals. Poisoning by certain metals, such as lead (lead encephalitis), can cause encephalitis in some individuals.

In addition, a number of risk factors apply only to the forms of encephalitis caused by contact with mosquitoes and ticks (arthropod-borne encephalitis). These include:

• Time of year. Because birds and mosquitoes tend to mate in the warmer summer months, this time of the year is also when most cases of encephalitis are reported.
  
  
• Geography. Certain locations are more suitable for mosquitoes and ticks than others. Mosquitoes often lay their eggs in areas with standing water, whereas ticks usually live in areas with dense vegetation. Children who visit or live in such areas are at increased risk of contracting encephalitis.
  
  
• Outdoor activity. Children who spend a proportionately large amount of time outdoors are at greater risk for contracting arthropod-borne encephalitis, particularly during an outbreak.

Cases of arthropod-borne encephalitis tend to occur in clusters within certain regions or time periods, and therefore, are better-known forms of the disease. However, they are less common than the other potential causes of encephalitis, including:

• Herpes simplex virus (HSV). This infection can lead to herpes simplex encephalitis (HSE). Though uncommon, HSE is the leading cause of fatal encephalitis cases in the United States. Up to half of newborns whose brains are infected with this virus will die from it, according to the American Academy of Physicians. Two types of HSV infections can cause HSE:
  
  
• • HSV type 1 (HSV-1) is generally recognized as the virus that causes the common cold sores or fever blisters around the mouth area. Although incredibly rare (affecting approximately two out of every 1 million people each year), HSV-1 is responsible for nearly all cases of HSE in older children and adults. However, studies have shown that people with HSV-1 who have cold sores are no more likely to contract encephalitis than those with HSV-1 who do not have cold sores.
    
    In addition, some people may have a genetic tendency for HSE caused by HSV-1, according to a recent study. Researchers from the Necker Medical School in Paris, France have identified a single gene (UNC93B1) that predisposes individuals to encephalitis caused by HSV-1. People who inherit two mutated copies of the UNC93B1 gene appear to be at higher risk of contracting encephalitis from an HSV-1 infection. Results from the study also revealed that a significant portion of patients with HSE caused by HSV-1 had parents who were blood relatives (e.g., first or second cousins) and were therefore at higher than normal risk of inheriting two copies of the faulty gene. 
    
    
  • HSV type 2 (HSV-2) is more commonly known as the virus that causes genital herpes. Newborns can contract encephalitis at the time of delivery if the mother has active HSV-2.
    
    
• Childhood infections such as German measles (rubella), measles (rubeola) and mumps. In rare instances, children can develop encephalitis after recovering from these conditions. When encephalitis does occur, it is usually in reaction to antibodies that have developed in the immune system. Encephalitis infection in children under these circumstances tends to be moderate.
  
  
• Cytomegalovirus (CMV) infection. CMV is a member of the herpes virus group and is transmitted through contact with infected body fluids (e.g., saliva, urine, semen, breast milk). The Centers for Disease Control and Prevention (CDC) estimates that between 50 and 85 percent of adults in the United States contract CMV by the age of 40, although most people never develop symptoms. In rare cases, encephalitis can be caused by CMV.
  
  
• Varicella-zoster virus. Responsible for chickenpox and shingles, this virus can cause what tends to usually be mild encephalitis in children and adults.
  
  
• Epstein-Barr virus. Known to cause mononucleosis, Epstein-Barr virus can also cause fatal encephalitis. However, the majority of encephalitis cases that result from Epstein-Barr virus tend to be comparatively less severe than other cases of encephalitis.
  
  
• HIV (human immunodeficiency virus). HIV, the virus that causes acquired immune deficiency syndrome (AIDS) can cause encephalitis in patients, principally in the early stages of illness.
  
  
• Rabies. Although incidences of rabies are extremely rare, raccoons are the most common carriers of the disease in the United States. Occasionally, rabies can cause encephalitis in humans.  
  
  
• Bacterial infections. In rare cases, infections such as bacterial meningitis can cause encephalitis.
  
  
• Toxoplasmosis. Caused by the toxoplasma gondii parasite. People can get toxoplasmosis through infected food or water or from coming in contact with infected cat feces. In rare case, toxoplasmosis can cause encephalitis.
  
  
• Roundworm infection. This usually occurs as a result of exposure to raccoon feces.

Arthropods are groups of animals with hard exoskeletons, segmented bodies and jointed limbs, such as mosquitoes and ticks. A virus transmitted by mosquitoes or ticks to an animal or person while taking a blood meal is known as an arbovirus.

Several arboviruses, usually named for the area in which they were discovered, can cause arthropod-borne encephalitis infection in humans. Such infected mosquitoes or ticks that serve as vectors (carriers or transmitters) are a growing health concern.

A mosquito feeding on an encephalitis-infected animal becomes a vector of the disease for the remainder of its lifespan. Once infected, the animal briefly exhibits very high levels of the virus in its blood until immunity develops and recovery can occur. The mosquito then infects the next animal on which it feeds, thus passing the virus to more animals. Birds, horses, rabbits, chipmunks, bats, skunks, cats, squirrels and other small mammals living in areas with high mosquito populations typically serve as hosts to encephalitis and other related diseases.

This feeding cycle usually continues without considerable harm to either the vector or host, and without reaching humans. Mosquitoes tend to bite birds and other small mammals first, with humans being bitten as strictly a second choice. However, certain unusual conditions, such as environmental disasters or inclement weather, can increase the risk of human infection by increasing infected mosquito populations in a given area.

The most common causes of arthropod-borne encephalitis through arboviruses are:

• Japanese encephalitis (JE) virus. Although vaccines are available, JE is the most lethal and common arboviral (mosquito or tick borne) encephalitis virus worldwide. The Centers for Disease Control and Prevention (CDC) estimates that 30,000 to 50,000 cases of JE occur each year in Asia, with approximately 15,000 of those resulting in death. However, an average of only about one case per year of JE virus is reported in Americans who live or travel to Asia. Approximately 30 percent of JE virus survivors retain severe neurological impairment. JE virus is prevalent in many tropical areas of Asia and the Indian subcontinent, with epidemics occurring most frequently in the summer months. Water birds tend to be the primary host. However, some agricultural animals (e.g., pigs) can also host the disease.
  
  
• West Nile virus. A relative newcomer in the United States, West Nile virus first appeared in America in 1999. West Nile virus is more commonly found in parts of Africa, Asia, Europe and the Middle East. Like with most other forms of encephalitis, birds serve as the main animal hosts. However, the disease can also be spread by humans during childbirth, breastfeeding, organ transplant and blood transfusions. Encephalitis caused by this arbovirus can be severe in older adults and/or those with compromised immune systems. In some cases, the virus may only cause fever and may not involve the nervous system (as meningitis and encephalitis do). Nonetheless, people infected with West Nile virus may experience chronic health problems such as fatigue, headaches, depression and tremors, according to a recent study. And patients with relatively benign West Nile fever can be just as likely to experience these long-term health consequences as those who are hospitalized with the more severe West Nile virus-related illnesses meningitis or encephalitis, according to the same study. In 2006, about 4,200 cases of infection by this virus were reported to the CDC, but fewer than 1,500 of them involved meningitis or encephalitis.
  
  
• Lyme disease. Transmitted by ticks typically found in rural and wooded areas of North America, Canada and Europe, Lyme disease can cause encephalitis in rare instances.
  
  
• Tick-borne encephalitis (TBE) virus. TBE virus is unique in that it is produced by three closely affiliated viruses: the western European subtype, the Siberian subtype and the far eastern subtype. A variety of host mammals and tick vectors throughout these regions maintain TBE virus through different natural cycles. Humans tend to be exposed to TBE virus in warmer areas during the spring and summer, as well as throughout the Mediterranean during fall and winter. In rare cases, infection with TBE virus can occur through the consumption of unpasteurized dairy products from sheep, goats or cows.
  
  
• Colorado tick fever virus. Occasionally, people stricken with Colorado tick fever virus develop either encephalitis or meningitis (inflammation of the membranes lining the brain). The Colorado tick fever virus is transmitted via the wood tick in parts of the western United States and Canada. Due to the mountainous geography of the region, wood ticks tend to live in elevations ranging from 4,000 to 10,000 feet (1,219 to 3,048 meters). Colorado tick fever virus can be spread between the months of March and September. However, peak months for transmission tend to be from April to June.
  
  
• Western equine encephalitis (WEE) virus. The WEE virus infects mainly horses in the central and western plains areas of North America. Flooding of these areas is common and is thought to precipitate outbreaks of WEE during hotter summer months. Significant outbreaks of WEE were common in this region during the 1950s and 1960s. However, a variety of factors have reduced outbreaks substantially since that time, including improved horse vaccination methods and declining horse populations. Very few adults infected with the WEE virus actually develop encephalitis.  However, death or serious complications (e.g., brain damage) can occur in very rare cases, most notably in small children and infants.

Signs or symptoms of encephalitis (inflammation of the brain) can vary in scope, severity and duration. In most cases, symptoms do not tend to be serious. However, encephalitis can be fatal in some instances.

Symptoms of encephalitis can take anywhere from one to 30 days to appear, although most symptoms become apparent within five to 15 days after the initial infection. Some possible symptoms, which may range in severity and warrant medical attention, include the following:

• Drowsiness or lethargy (possibly extreme)
• Headache (possibly severe)
• Photophobia (aversion or sensitivity to light)
• Stiffness in the neck or back
• Fever
• Convulsions or vomiting
• Loss of balance
• Difficulty moving an arm or leg
• Difficulty walking
• Double vision
• Loss of consciousness
• Loss of sensation anywhere in the body
• Memory difficulties
• Problems with speech or hearing
• Seizures
• Sudden personality changes
• Bleeding within the brain (intracerebral hemorrhage)
• Paralysis
• Confusion
• Muscle weakness

Symptoms of encephalitis can be much more difficult to detect in infants. Infants younger than 3 months who have a fever higher than 100.4 degrees Fahrenheit (38 degrees Celsius) require immediate medical attention. Other symptoms typically associated with encephalitis in infants, include:

• Full or bulging “soft spot” (fontanel) on the head
• Body stiffness, or floppiness or decreased body tone
• Crying that is ongoing, or that worsens when picking up or touching the child
• Vomiting
• Lethargy
• Poor appetite

Encephalitis may occur along with inflammation of the membranes lining the brain (meningitis). When physicians are trying to diagnose meningitis, encephalitis or some overlap of the two, a distinguishing factor is often the patient’s brain function. Patients with meningitis might exhibit discomfort, lethargy or distraction by headache, but their cognitive function remains normal. However, individuals with encephalitis commonly exhibit aberrations in brain function, like speech or motion disorders, altered cerebral status or motor or sensory problems. Left untreated, encephalitis can lead to coma and death.

A physician will compile a thorough medical history of the child and perform a complete physical examination. The physician is also likely to ask whether the child has recently had a cold or other respiratory illness, gastrointestinal illness or tick bite. In addition, parents will be asked whether the child has been around pets or other animals, or has traveled to certain areas of the country that might be high-risk areas for contracting viruses that can cause encephalitis.

There are several ways in which physicians may test for the presence of encephalitis (inflammation of the brain). Diagnosis methods may include:

• Blood testing. Removal of a sample of blood (usually from a vein) for laboratory analysis. Certain encephalitis types, such as West Nile encephalitis virus, are detectable through blood testing. Analysis of blood may show a rise in antibodies to a virus or other indicators necessary to make a diagnosis.
  
  
• Brain imaging. A CAT scan (computed axial tomography) or MRI (magnetic resonance imaging) that produces images of the brain may reveal swelling consistent with encephalitis. Pressure within the brain can often be observed through brain imaging, providing valuable insight as to the likelihood of encephalitis infection prior to performing a spinal tap.

• Spinal tap (lumbar puncture). Involves inserting a needle directly into the lower spine area to extract cerebrospinal fluid (CSF) for laboratory testing. A spinal tap is a common method used to diagnose encephalitis. Advances in the testing of DNA (the molecule that encodes genetic information) have made it possible to diagnose encephalitis through more detailed examination of CSF. This may reveal the presence of the virus directly or indirectly (e.g., a heightened white blood cell count which indicates the body is fighting infection). Sometimes a spinal tap may be nondiagnostic.
  
  
• Electroencephalography (EEG). A measure of the brain’s electrical activity. Electrodes that monitor electrical impulses of the brain are pasted or otherwise attached to the scalp. The electrodes send the information of the brain’s activity to an EEG machine for recording on a moving sheet of paper. Abnormal readings may indicate the presence of encephalitis, however normal results do not categorically rule out the presence of encephalitis.
  
  
• Brain biopsy. Removal of a sample of brain tissue for laboratory analysis. The patient is anesthetized and a small hole is drilled into the skull, followed by the insertion of a needle into the brain tissue. Computer-imaging techniques such as x-rays or MRI aid in this technique. A brain biopsy may be necessary in rare instances when diagnosis of encephalitis through other methods is not possible. This test is not without risks and is not commonly performed.

The primary goal in treating any child with encephalitis is to reduce swelling of the brain and prevent any associated complications. Treatment for a mild case of encephalitis consists primarily of rest, maintaining a healthy diet and drinking plenty of liquids. Pain and fever relievers such as acetaminophen can help reduce or eliminate headache and fever. The use of anti-inflammatory drugs such as corticosteroids may help reduce head puffiness or pressure. Aspirin should never be provided to children due to the rare risk of Reye Syndrome.

However, more serious encephalitis cases may require more significant treatments. In some cases, this may require hospitalization and close monitoring. Sometimes, encephalitis can cause the brain to swell to the point that there is little room left in the skull. This increases pressure in the skull, which can damage the brain.

In such situations, the patient’s intracranial pressure will likely be measured in one of two ways. One technique places a small hollow tube (catheter) into the fluid-filled space in the brain (ventricle). Another technique places a small hollow device (bolt) through the skull into the space just between the skull and the brain.

These devices are attached to a monitor that gives a constant reading of the pressure inside the skull so that a rise in pressure can be treated immediately. Once the brain’s swelling has gone down, the device is removed.

Severe cases of encephalitis may also require the use of a breathing machine to aid the child’s respiration. Nutritional supplements or feeding tubes may be employed to ensure adequate nutrition.

Other treatments associated with encephalitis include:

• Medications. Certain medications may be prescribed to treat moderate to severe encephalitis. Antibiotics are sometimes used to prevent an associated bacterial infection known as a superadded infection. Anticonvulsant medications can help treat a child’s seizures.
  
  
• Dimming of lights. This may help alleviate headaches. However, lights should not be dimmed enough to create shadows, which may cause hallucinations.
  
  
• Rehabilitative treatment (e.g., speech therapy, physical therapy). This can help address lasting brain damage, such as behavioral changes or problems with physical mobility.

Most children who are treated early and appropriately make a full and uncomplicated recovery following a bout of encephalitis. In rare cases, encephalitis can cause permanent brain damage and learning disabilities, speech problems, memory loss and lack of muscle control. In such cases, speech therapy, physical therapy or occupational therapy may be helpful.

Although encephalitis itself is not contagious, the viruses that cause the disease can be transmitted from an infected person to a child. The most effective way to prevent encephalitis infection is to avoid viruses that may cause the disease, although vaccines are available for Japanese encephalitis and tick-borne encephalitis. Children should avoid contact with anyone who has encephalitis.

It is equally important for children to be immunized against diseases such as chickenpox, measles (rubeola), mumps and German measles (rubella) that are associated with encephalitis. Children should receive these immunizations according to the schedule established by their pediatrician.

It is possible for anyone to contract mosquito-borne encephalitis. Accordingly, there are no fail-safe measures one can take to prevent exposure. However, there are certain strategies that will help reduce the likelihood that a child will become infected if an outbreak of the disease is apparent. They include:

• Wearing protective clothing. Covering a child’s arms and legs with long sleeves and pants between dusk and dawn is effective at reducing mosquito bites.
  
  
• Using mosquito repellant with DEET. Mosquito repellant with a 10 to 30 percent concentration of DEET should be applied to a child’s skin and clothing in areas where mosquitoes are prevalent. As a general rule, a 10 percent concentration of DEET will last approximately two hours, with higher concentrations lasting longer durations. Parents of children under 2 months of age should not use repellants with DEET on their child. Pregnant women also should not use repellants with DEET. If ingested, DEET can cause birth defects in fetuses and death in small children.
  
  
• Keeping mosquitoes outside. Preventing holes in screened doors and windows helps to limit mosquitoes in the home.
  
  
• Avoiding mosquito habitats. If possible, have children avoid outdoor activities in areas where mosquitoes are common.
  
  
• Removing outside water sources. Mosquitoes lay eggs in standing water. Emptying common items like birdbaths, drains, wheelbarrows, and flowerpots will help reduce mosquito populations. Removing other objects where water can accumulate will also help, such as old tires or containers.
  
  
• Paying attention to warning signs. Signs such as sick or dying birds and/or other animals dying from unknown causes may indicate an outbreak of encephalitis. If spotted, be sure to report such occurrences to the local health department.

Tick bites can also be a source of Lyme disease, which can lead to encephalitis. The following steps can help lower a child’s risk of tick bites:

• Limit the child’s contact with soil, leaves and vegetation
  
  
• Urge the child to wear long-sleeved, light-colored shirts and long pants
  
  
• Check the child and any pets frequently for ticks

Preparing questions in advance can help patients and parents have more meaningful discussions with physicians regarding their or their child’s treatment options. The following questions related to encephalitis may be helpful:

1. What can I do to prevent my child’s exposure to encephalitis?
   
   
2. How concerned should I be about the potential that my child will contract encephalitis?
   
   
3. What signs and symptoms might indicate that my child has encephalitis?
   
   
4. What activities put my child at greatest risk for exposure to encephalitis?
   
   
5. How can I limit mosquito and tick populations around my house?
   
   
6. What diagnostic tests for encephalitis might my child need to undergo, and what do they involve?
   
   
7. What type of encephalitis does my child have?
   
   
8. What are my child’s treatment options? What are the pros and cons of these methods?
   
   
9. Can my child get complications from encephalitis?
   
   
10. Should my family be tested for the condition that caused my encephalitis?
    
    
11. Should I alert school authorities and other parents of my child’s infection?