The Facts about Encephalitis

Infections in the brain and spinal cord can cause dangerous inflammation. This inflammation can produce a wide range of symptoms, including fever, headache, or confusion, and in extreme cases, can cause brain damage, stroke, seizures, or even death.

Inflammation of the brain is called encephalitis. Myelitis is an infection of the spinal cord. When both the brain and the spinal cord become inflamed, the condition is called encephalomyelitis.

Causes
Encephalitis can be caused by bacterial infection and, most often, viral infections. Usually, the body's immune system is able to contain and defeat an infection. But if the infection passes into the blood stream and then into the cerebrospinal fluid that surrounds the brain and spinal cord, it can affect the nerves and travel to the brain, causing inflammation. This swelling can harm or destroy nerve cells and cause bleeding in the brain.

Several thousand cases of encephalitis are reported each year, but many more may actually occur since the symptoms may be mild to non-existent in most patients.

Anyone can get encephalitis, although people with weakened immune systems, including those persons with HIV or those taking immunosuppressant drugs, are at the highest risk.

There are two types of encephalitis. Primary encephalitis, also called acute viral encephalitis, is caused by a direct viral infection of the spinal cord and brain. The infection may be focal (located in only one area) or diffuse (located in many different areas). Secondary encephalitis, also known as post-infective encephalitis, can result from complications of a current viral infection. Secondary encephalitis that results from an immunization or earlier viral infection is known as acute disseminated encephalitis. This illness often occurs 2 to 3 weeks following the initial infection.

Most cases of encephalitis in the United States are caused by enteroviruses, herpes simplex virus types 1 and 2, a bite from a rabid animal (rabies virus), or arboviruses, which are transmitted from infected animals to humans through the bite of an infected tick, mosquito, or other blood-sucking insect. Lyme disease, a bacterial infection spread by tick bite, can cause encephalitis.

Herpes simplex encephalitis (HSE) is responsible for about 10% of all encephalitis cases, with a frequency of about 2 cases per million persons per year. More than half of untreated cases are fatal. About 30% of cases result from the initial infection with the herpes simplex virus; the majority of cases are caused by reactivation of an earlier infection.

HSE due to herpes simplex virus type 1 (which causes cold sores or blisters around the mouth or eyes) can affect any age group but is most often seen in persons under age 20 or over age 40. This rapidly progressing disease is the single most important cause of fatal sporadic encephalitis in the US. The virus is transmitted through contact with an infected person.

Symptoms include headache and fever for up to 5 days, followed by personality and behavioral changes, seizures, partial paralysis, hallucinations, and altered levels of consciousness. Brain damage in adults and in children beyond the neonatal period is usually seen in the frontal and temporal lobes and can be severe.

Herpes simplex virus type 2 (genital herpes) is most often transmitted through sexual contact. An infected mother can transmit the disease to her child at birth, through contact with genital secretions, but this is uncommon. In newborns, symptoms such as lethargy, irritability, tremors, seizures, and poor feeding generally develop between 4 and 11 days after delivery.

Powassan encephalitis is the only well-documented tick-borne arbovirus in the United States and Canada. Symptoms are noticed 7-10 days following the bite and may include headache, fever, nausea, confusion, partial paralysis, and coma. Permanent neurologic damage occurs in about half of all cases and death in about 10% to 15% of all cases.

Four common forms of mosquito-transmitted viral encephalitis are seen in the United States: Equine, LaCrosse, St. Louis and West Nile.

Equine encephalitis affects horses and humans.

• Eastern equine encephalitis also infects birds that live in freshwater swamps of the eastern US seaboard and along the Gulf Coast. In humans, symptoms are seen 4-10 days following transmission and include sudden fever, general flu-like muscle pains, and headache of increasing severity, followed by coma and death in severe cases. About half of infected patients die from the disorder. Fewer than 10 human cases are seen annually in the United States.
  
• Western equine encephalitis is seen in farming areas in the western and central plains states. Symptoms begin 5-10 days following infection. Children, particularly those under 12 months of age, are affected more severely than adults and may have permanent neurologic damage. Death occurs in about 3% of cases.
  
• Venezuelan equine encephalitis is very rare in this country. Children are at greatest risk of developing severe complications, while adults generally develop flu-like symptoms. Epidemics in South and Central America have killed thousands of persons and left others with permanent, severe neurologic damage.

LaCrosse encephalitis occurs most often in the upper midwestern states (Illinois, Wisconsin, Indiana, Ohio, Minnesota, and Iowa) but also has been reported in the southeastern and mid-Atlantic regions of the country. Most cases are seen in children under age 16. Symptoms such as vomiting, headache, fever, and lethargy appear 5-10 days following infection. Severe complications include seizure, coma, and permanent neurologic damage. About 100 cases of LaCrosse encephalitis are reported each year.

St. Louis encephalitis is most prevalent in temperate regions of the United States but can occur throughout most of the country. The disease is generally milder in children than in adults, with elderly adults at highest risk of severe disease or death. Symptoms typically appear 7-10 days following infection and include headache and fever. In more severe cases, confusion and disorientation, tremors, convulsions (especially in the very young), and coma may occur.

West Nile encephalitis was first clinically diagnosed in the United States in 1999; 284 people are known to have died of the virus the following year. There were 9,862 reported cases of human West Nile disease in calendar year 2003, with a total of 560 deaths from this disorder over 5 years. The disease is usually transmitted by a bite from an infected mosquito, but can also occur after transplantation of an infected organ or transfusions of infected blood or blood products. Symptoms are flu-like and include fever, headache, and joint pain. Some patients may develop a skin rash and swollen lymph glands, while others may not show any symptoms. At highest risk are elderly adults and people with weakened immune systems.

Transmission
Some forms of encephalitis are contagious and can be spread through contact with saliva, nasal discharge, feces, or respiratory and throat secretions (often spread through kissing, coughing, or sharing drinking glasses, eating utensils, or such personal items as toothbrushes, lipstick, or cigarettes). For example, people sharing a household, at a day care center, or in a classroom with an infected person can become infected. Because the disease can occur suddenly, anyone who is suspected of having encephalitis should immediately contact a doctor or go to the hospital.

Signs and Symptoms
Encephalitis is characterized by seizures, stupor, coma, and related neurological signs. In more severe cases, neurological symptoms may include nausea and vomiting, confusion and disorientation, drowsiness, sensitivity to bright light, and poor appetite.

Patients with encephalitis often show mild flu-like symptoms. In more severe cases, patients may experience problems with speech or hearing, double vision, hallucinations, personality changes, loss of consciousness, loss of sensation in some parts of the body, muscle weakness, partial paralysis in the arms and legs, sudden severe dementia, impaired judgment, seizures, and memory loss.

Important signs of encephalitis to watch for in an infant include vomiting, body stiffness, constant crying that may become worse when the child is picked up, and a full or bulging fontanel (the soft spot on the top of the head).

Diagnosis
Following a physical exam and medical history to review activities of the past several days (such as recent exposure to insects or animals, any contact with ill persons, or recent travel), the doctor may order various diagnostic tests to confirm the presence of infection and inflammation. Early diagnosis is vital, as symptoms can appear suddenly and escalate to brain damage, hearing and/or speech loss, blindness, or even death.

A neurological examination involves a series of tests designed to assess motor and sensory function, nerve function, hearing and speech, vision, coordination and balance, mental status, and changes in mood or behavior. Doctors may test the function of the nervous system through tests of strength and sensation, with the aid of items including a tuning fork, small light, reflex hammer, and pins.

Laboratory screening of blood, urine, and body secretions can help detect and identify brain and/or spinal cord infection and determine the presence of antibodies and foreign proteins. Such tests can also rule out metabolic conditions that have similar symptoms. For example, a throat culture may be taken to check for viral or bacterial organisms that cause encephalitis.

Analysis of the cerebrospinal fluid that surrounds and protects the brain and spinal cord can detect infections in the brain and/or spinal cord, acute and chronic inflammation, and other diseases. In a procedure known as a spinal tap (or lumbar puncture), a small amount of cerebrospinal fluid is removed by a special needle that is inserted into the lower back. The skin is anesthetized with a local anesthetic prior to the sampling. The fluid, which is completely clear in healthy people, is tested to detect the presence of bacteria or blood, as well as to measure glucose levels and white blood cells (elevated white blood cell counts are a sign of infection). The procedure is usually done in a hospital and takes about 45 minutes.

Computer-assisted imaging (CT scan or MRI) can reveal signs of brain inflammation, internal bleeding or hemorrhage, or other brain abnormalities.

Electroencephalography, or EEG, can identify abnormal brain waves by monitoring electrical activity in the brain through the skull. Among its many functions, EEG is used to help diagnose certain seizure disorders, brain damage from head injuries, specific viral infections such as herpes virus, and inflammation of the brain and/or spinal cord. This painless, risk-free test can be performed in a doctor's office or at a hospital or testing facility.

Treatment
Persons who are suspected of having encephalitis should receive immediate, aggressive medical treatment. Both diseases can progress quickly and have the potential to cause severe, irreversible neurological damage.

Antiviral drugs used to treat viral encephalitis include acyclovir and ganciclovir. Very mild cases of encephalitis may be monitored at home by the physician and a caregiver. Supportive care includes fluids, bed rest, and over-the-counter analgesics to reduce fever and headache. More severe cases may require hospitalization. Anticonvulsants may be prescribed to stop or prevent seizures, along with sedatives to calm more severely infected persons and drugs to counter nausea and vomiting. Corticosteroids and intravenous administration of carbohydrate solutions can reduce brain swelling. Patients with breathing difficulties may require artificial respiration.

Patients who experience severe brain inflammation may need physical, speech, and occupational therapy once the acute illness is under control.

Prevention
Good personal hygiene can reduce the risk of getting the disease from an infected person. Avoid sharing food, utensils, glasses, and other objects with a person who may be exposed to or have the infection. Wash hands often with soap and rinse under running water.

To lessen the risk of being bitten by an infected mosquito or other insect, people should limit outdoor activities at night, wear long-sleeved clothing when outdoors, use insect repellents that are most effective for that particular region of the country, and rid lawn and outdoor areas of free-standing pools of water, in which mosquitoes breed. Do not over-apply repellants, particularly on young children and especially infants, as chemicals may be absorbed through the skin.

Outcome
Outcome generally depends on the particular infectious agent involved, the severity of the illness, and how quickly treatment is given. In most cases, people with very mild encephalitis can make a full recovery, although the process may be slow.

Patients who experience only headache, fever, and stiff neck may recover in 2-4 weeks. Patients receiving treatment for encephalitis usually see some relief in 24-48 hours and recovery in about a month. In more serious cases, the disease can cause hearing and/or speech loss, blindness, permanent brain and nerve damage, behavioral changes, cognitive disabilities, lack of muscle control, seizures, and memory loss. These patients may need long-term therapy, medication, and supportive care.

This article is based on information provided by the National Institute of Neurological Disorders and Stroke.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.