Viral Encephalitis Diagnosis

  • Diagnosis

    Encephalitis is a general term that means inflammation of the brain.

    Encephalitis can occur two different ways: from direct infection of the brain, or from a previous infection that causes your immune system to attack your brain. Direct infection can be caused by many different agents, including bacteria, fungi, and viruses. This article will explore only viral causes of encephalitis. There are many encephalitis-causing viruses, so only causes, symptoms, and treatment related to the most common viruses will be discussed.

    Encephalitis can result from certain viral infections passed between humans, or from contact with infected animals or insects.

    Encephalitis can develop 5 to 10 days after some childhood illnesses (for example, chickenpox, measles, mumps, rubella, and polio). Fortunately, it is not common to get encephalitis after a viral illness. On rare occasions, encephalitis can occur weeks, months, or years after the initial viral infection. Vaccine programs have markedly reduced some of these diseases in the developed world.

    There are many viruses transmitted between humans that can lead to encephalitis. Viruses from the herpes group are familiar examples. Chickenpox, cytomegalovirus, and Epstein-Barr virus (the cause of infectious mononucleosis) are herpes viruses. All herpes viruses may cause encephalitis occasionally, but herpes simplex virus 1 is the most common culprit.

    The herpes simplex virus 1 causes herpes simplex encephalitis.

    Herpes simplex viruses occur throughout the world. About 90% of adults age 50 or older have been exposed to herpes simplex virus 1 at some time during their lifetime. Herpes simplex virus 1 is most commonly known for causing cold sores (fever blisters) on the lips or around the mouth area. The most common cause of non-epidemic (not affecting a large number of people at once) encephalitis in developed countries is the herpes simplex virus. About 30% of herpes encephalitis infections result from initial contact with the virus. However, 70% of encephalitis cases occur years after the first infection. This happens when virus particles that have been dormant in the brain since the initial infection become active. While it is not known what causes the herpes simplex virus to reactivate, it is thought that a weakened or suppressed immune system may play a role.

    Ticks or mosquitoes spread certain encephalitis-causing viruses to people.

    Insect-transmitted viruses are the most common cause of epidemic viral encephalitis in the U.S. Viruses that can be transmitted to humans from mosquitoes or ticks are called arboviruses. Mosquitoes and ticks acquire these viruses from feeding on an infected host. Depending on the specific virus, birds, horses, small animals, or rodents can act as hosts. After the mosquito bites an infected host, the virus multiplies inside the mosquito. When it feeds or bites again, the mosquito can transmit the virus to the person or animal it bites. (For additional information, see the Patient Guide Insect Stings and Bites).

    The most common insect-borne encephalitis in the U.S. is St. Louis encephalitis. It can occur in people of all ages, in either rural or urban areas.

    The St. Louis encephalitis virus is transmitted by mosquitoes that bite infected birds before biting humans. Older adults infected by St. Louis encephalitis have a greater chance of their illness being serious. While overall only 7% of those with St. Louis encephalitis die, 20% of those over the age of 60 do not survive. For those who live, recovery tends to be slow. Recovering patients suffer from unstable emotions, trouble concentrating, forgetfulness, and tremors. Most cases of St. Louis encephalitis occur in mid- to late-summer, or whenever the mosquito population of the particular region is active.

    California encephalitis is caused by an infection with the LaCrosse virus.

    California encephalitis is found mainly in midwestern, north central, and eastern regions of the U.S. In areas where it is commonly found, as many as 20% of the human population have antibodies to the virus. This means they have been exposed to the virus in the past; however, most of those exposed did not develop an illness. The virus exists in small woodland mammals like chipmunks and squirrels, and is transmitted by mosquitoes to humans. The disease occurs primarily in children under 15 years of age. Illness is rare and the mortality (death) rate is low. Unfortunately, about 10-15% of California encephalitis survivors may have lasting difficulty with thought, movement, and overall functioning.

    Western equine encephalitis was common in western and central areas of the U.S. and Canada from the 1930s to the 1950s, but is less common now.

    Horses are the primary carriers of this virus. Mosquitoes bite infected horses, then pass the virus on to other horses and humans. Children typically suffer more severely from western equine encephalitis, with 3% dying and 5% to 30% suffering permanent impairment.

    Eastern equine encephalitis occurs primarily in swampy areas along the eastern and Gulf coasts of the U.S. from June through October.

    Eastern equine encephalitis has a high fatality rate, and there is a high risk of neurological problems in those who survive. Only 38 cases of eastern equine encephalitis were reported in the U.S. between 1988 and 1994. It has also been found in some inland midwestern states, and may occur year-round in southern states. Older adults are more at risk to become ill with eastern equine encephalitis than younger individuals who are exposed.

    The West Nile virus has recently emerged in the U.S..

    Common in Africa, Asia, and the Middle East, the West Nile virus first appeared in the Americas in New York City during the summer of 1999. The virus is carried by bird populations, and is passed on to humans through mosquito bites. Encephalitis caused by the West Nile Virus is uncommon and usually mild, but can be fatal. During the first New York outbreak, 62 patients suffered from severe disease, and seven people died during the summer and fall of 1999. As of 2005, the virus had infected people in 48 states and Washingon, DC. (More information on West Nile Virus is available in the patient guide West Nile Virus).

    Other types of insect-transmitted encephalitis are found in different parts of the world.

    Powassan is a rare type of encephalitis transmitted to humans from infected birds or small mammals by a tick. Powassan is found in the northern U.S. and in Canada. Venezuelan equine encephalitis primarily occurs in Central and South America. Japanese encephalitis occurs throughout Asia, and tick-borne encephalitis occurs in rural areas of Europe and Russia. These are just a few examples of infectious diseases that you may encounter when traveling abroad. If you plan to travel outside of the U.S., it is important to discuss region-specific health concerns with your clinician. For more information in infectious diseases outside of the U.S., see the Patient Guide International Travel Advice.

    Encephalitis can also be caused by rabies.

    Bats, foxes, and skunks are some of the common carriers of the rabies virus. You should never handle a dead animal with your bare hands, because diseases (including rabies) can be transmitted even after death. Many people are under the misconception that rabies is only caught through a bite from an infected animal. However, simply having a cut or sore exposed to the saliva of an infected animal can transmit the disease. Airborne transmission of rabies has been proven in caves heavily infested with bats. In cabins and in houses where bats have invaded the attic or other areas, humans have been bitten while they sleep. Although common in other parts of the world, relatively few human cases of rabies occur in the U.S., due to widespread animal vaccinations.

    If a bite or contact with a possibly infected animal occurs, medical attention should be sought immediately. A person must receive immunization against rabies within two days of exposure to the virus to prevent the disease. Once symptoms of the disease begin, it will likely be fatal.

    (For more information on bite trauma, consult the Patient Guide Animal and Human Bites).

    The most common signs of acute viral encephalitis are fever, headache, and a change in level of consciousness.

    Other common signs are the eyes becoming sensitive to light (photophobia), confusion, and sometimes seizures.

    Meningitis may sometimes occur with encephalitis. Meningitis is the inflammation of the membranes (meninges) surrounding the brain and spinal cord. Stiffness of the neck is the cardinal sign of meningitis, and occurs in addition to the symptoms of encephalitis.

    Some people exposed to insect-borne encephalitis viruses do not develop symptoms of encephalitis. They may only experience low-grade fever, drowsiness, and flu-like symptoms of malaise (general feeling of illness) and myalgia (muscle aches). Headache, vomiting, and sensitivity to light may follow.

    Some viruses may affect specific areas of the brain, including problems with speech, movement, and behavioral (personality) changes. Epstein-Barr virus, St. Louis encephalitis, eastern equine encephalitis, and enterovirus infections can have different symptoms, depending on the part(s) of the brain affected.

    Herpes simplex encephalitis is known to cause additional symptoms. Fever, headache, decreased level of consciousness, and confusion may occur. Other symptoms may include seizures, difficulty speaking, inability to move one side of the body, memory loss, and/or behavioral changes.

    Rabies may produce symptoms days to months after the exposure.

    Frequently there is pain, numbness, or tingling at the bite wound. It may take 30-70 days after exposure for rabies symptoms to begin. Because of this, sometimes the patient cannot recall a bite or animal exposure. Early symptoms over the first 5-7 days of illness include fever, malaise, nausea, vomiting, and headache. Behavioral symptoms may also appear, including anxiety, depression, delirium (sudden confusion and change in mental status), hallucinations, and intolerance to touch, sounds, and visual stimuli. Later symptoms include agitation, muscle spasms, and fear of the sight of water (hydrophobia). It may become difficult to swallow liquids or saliva. Eventually, coma and death will occur. Some patients with rabies have paralysis that begins in the legs and moves upward to involve the arms, eventually leading to coma.

    Crowded living conditions and poor sanitation can increase the risk of some types of encephalitis. Contact with infected animals can put humans at risk of encephalitis.

    Some viruses are transmitted between humans by respiratory (airborne) and intestinal-borne routes. Measles, mumps, and chickenpox are examples of respiratory viruses. Poliovirus, coxsackie, and echovirus are examples of intestinal viruses. Frequent and thorough hand washing with soap and water can decrease the spread of viruses and other illness-causing germs.

    Living in or traveling to an area where insects are known to carry encephalitis-causing viruses increases your risk for getting insect-borne encephalitis. In the U.S., you are most likely to get insect-borne encephalitis between June and October.

    The months when risk of insect-transmitted viral infection is highest can vary, depending on the geographical region and the prevalence of mosquitoes and ticks that season.

    Older people are at a greater risk of serious disease and death from West Nile and St. Louis encephalitis. However, California encephalitis poses a greater danger to children under 15 years of age than to older people. Having a weakened immune system puts you at risk for many types of encephalitis.

    For example, people with weakened immune systems due to HIV are at higher risk for infection from many viruses that cause encephalitis. Similarly, transplant recipient patients who must be given medication to prevent organ or tissue rejection are more vulnerable to organisms that cause viral encephalitis.

    If your clinician suspects that you have encephalitis, they will ask questions about your vaccination history, exposure to ticks, mosquitoes, and animals, and any recent trips you have taken.

    Many diseases produce symptoms that mimic those of encephalitis. Therefore, your clinician will obtain a thorough history before making a diagnosis. Your clinician will also consider the season, as most epidemic encephalitis cases occur during mosquito and tick season.

    Because the chance of illness from an insect bite is small, you do not need to see your clinician about a simple insect bite. However, if you or a family member develops symptoms such as high fever, weakness, confusion, or headaches, you should seek medical attention immediately.

    Several tests may be run to determine whether or not you have encephalitis.

    Unless swelling in your brain makes it dangerous, your doctor may perform a lumbar puncture. During a lumbar puncture, a needle is inserted into your back to remove a sample of the fluid surrounding your brain and spinal cord (cerebrospinal fluid, or CSF). This fluid will then be examined in a laboratory for evidence of infection.

    Your doctor may also order a magnetic resonance imaging (MRI) or computed tomography (CT) scan, primarily to rule out diseases that have similar symptoms as viral encephalitis. Your doctor may perform an electroencephalography exam (EEG)—a recording of the brain's electrical activity—to look for unusual brain wave patterns. A relatively new test that identifies the genes of certain microbes in the CSF may also help in the diagnosis. In rare cases, a brain biopsy (removal of tissue for microscopic examination) may be necessary to diagnose encephalitis.

    Practice proper cleanliness to limit the spread of viruses between individuals.

    To prevent spreading germs that cause illness, wash your hands frequently, especially before eating and after using the bathroom. Teach children to wash their hands frequently also. Avoid crowded locations during the cold weather season, cover your mouth when coughing or sneezing, and do not share food, cups, or utensils with others.

    When outdoors, take steps to avoid mosquito and tick bites.

    Wear long pants, socks, and long-sleeved shirts, preferably in light colors. Apply insect repellent that contains 30% DEET to exposed skin and clothing when you are outside. Children should use insect repellant that contains no more than 10% DEET, applied by an adult. Stay inside at dusk, dawn, and early evening, and do not wear floral fragrances or perfumes. Do not allow water to collect in bowls or other containers where mosquitoes can breed. Keep your screens in good repair, and clean gutters regularly. When you plan trips, ask wildlife and public health officials about the prevelance of insect-borne viruses in that region before traveling, and limit travel in times of unusually high activity. For more information on mosquito bite prevention, see the Patient Guide about West Nile virus.

    Vaccinations exist for some types of encephalitis that occur outside the U.S.

    You may be advised to get a vaccination for Japanese encephalitis if you are traveling to Asia in the summer. However, this vaccination carries a small risk of allergic reaction. Immunizations against tick-borne encephalitis (common in rural areas in Europe and Russia) are available, but can cause Guillain-Barré syndrome, a serious neurological disorder. Ask your clinician about the risks versus the benefits of these and any other vaccinations you may need before travelling outside of the U.S.

  • Prevention and Screening

    Practice proper cleanliness to limit the spread of viruses between individuals.

    To prevent spreading germs that cause illness, wash your hands frequently, especially before eating and after using the bathroom. Teach children to wash their hands frequently also. Avoid crowded locations during the cold weather season, cover your mouth when coughing or sneezing, and do not share food, cups, or utensils with others.

    When outdoors, take steps to avoid mosquito and tick bites.

    Wear long pants, socks, and long-sleeved shirts, preferably in light colors. Apply insect repellent that contains 30% DEET to exposed skin and clothing when you are outside. Children should use insect repellant that contains no more than 10% DEET, applied by an adult. Stay inside at dusk, dawn, and early evening, and do not wear floral fragrances or perfumes. Do not allow water to collect in bowls or other containers where mosquitoes can breed. Keep your screens in good repair, and clean gutters regularly. When you plan trips, ask wildlife and public health officials about the prevelance of insect-borne viruses in that region before traveling, and limit travel in times of unusually high activity. For more information on mosquito bite prevention, see the Patient Guide about West Nile virus.

    Vaccinations exist for some types of encephalitis that occur outside the U.S.

    You may be advised to get a vaccination for Japanese encephalitis if you are traveling to Asia in the summer. However, this vaccination carries a small risk of allergic reaction. Immunizations against tick-borne encephalitis (common in rural areas in Europe and Russia) are available, but can cause Guillain-Barré syndrome, a serious neurological disorder. Ask your clinician about the risks versus the benefits of these and any other vaccinations you may need before travelling outside of the U.S.

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