Encephalitis is an inflammation of the brain, usually caused by a virus and is referred to as viral encephalitis. Encephalomyelitis is an inflammation of both the brain and spinal cord, also caused by a virus. Aseptic meningitis is an inflammation of the meninges (the lining around the brain and spinal cord), usually caused by a virus.
Several different viruses can infect the brain and spinal cord, including occasionally those that cause herpes and mumps. Some of these infections occur in epidemics, and some are spread by insects.
Some viruses don't primarily infect the brain and spinal cord but rather cause immune reactions that indirectly result in inflammation of these areas. This type of encephalitis (parainfectious encephalitis or postinfectious encephalitis) can follow measles, chickenpox, or rubella. The inflammation typically develops 5 to 10 days after a viral illness and can severely damage the nervous system.
Very rarely, a brain inflammation occurs weeks, months, or years after a viral infection. An example is subacute scierosing panencephalitis, a brain inflammation that occasionally follows measles and usually occurs in children.
Although the vast majority of individuals with encephalitis recover after a long period of time, inflammation may cause irreparable damage to the brain, bleeding within the brain, and even death. An estimated 10,000 to 20,000 cases of encephalitis are reported annually in the United States.
Viral brain infections can produce three different sets of symptoms. Some infections are mild, causing fever and a general feeling of illness, often without specific symptoms. Viral meningitis usually produces fever, headache, vomiting, weakness, and a stiff neck. Encephalitis disrupts normal brain function, causing personality changes, seizures, weakness of one or more parts of the body, confusion, sleepiness that can progress to coma, and the symptoms of meningitis.
Certain viruses produce additional symptoms. For example, the herpes simplex virus often induces repeated seizures in the early stages of encephalitis. The cerebrospinal fluid in herpes simplex encephalitis contains red blood cells in addition to white blood cells - this is unusual in other milder types of viral infection. This virus also causes swelling in the temporal lobe of the brain, which can be diagnosed early by a magnetic resonance imaging (MRI) scan begins to show changes only after severe damage has occurred.
Other signs and symptoms of encephalitis depend on which area of the brain is most affected; these may include an impaired ability to use or comprehend words or coordinate voluntary muscle movements, muscle weakness or partial paralysis on one side of the body, uncontrollable tremors or involuntary movements, and an inability to regulate body temperature.
Arboviruses, or viruses carried by insects, are among the most common causes of viral encephalitis. Some of the major arboviruses include:
Other viruses that commonly cause viral encephalitis include:
Less common causes include:
Not all cases of encephalitis are caused by viruses. Some nonviral causes of encephalitis include:
The following factors may increase an individual's risk for becoming infected with viral encephalitis:
Encephalitis is a serious condition, so diagnosis and initial treatment usually take place in a hospital setting. After performing a physical exam, a physician may take the following steps to diagnose the condition:
At first, doctors may have difficulty distinguishing viral or aseptic meningitis from bacterial meningitis, and encephalitis may closely resemble many other diseases that cause abnormal brain function. At the first sign of either of these conditions, doctors try to pinpoint the cause of the infection. They almost always perform a spinal tap to evaluate the cerebrospinal fluid. In viral infections, the number of white blood cells in the fluid is increased, but no bacteria are present. Culturing viruses from the fluid is difficult and takes many days.
Doctors also use immunologic tests that measure antibodies against viruses. Even with tests, a specific virus is identified less than half the time. The doctor may order a CT or MRI scan to be sure the symptoms aren't being caused by a brain abscess, stroke, or structural problem, such as a hematoma, aneurysm, or tumor.
The most effective way for an individual to prevent encephalitis is to avoid contracting viruses that lead to encephalitis:
Because encephalitis is a serious condition that can cause severe complications, treatment usually occurs in the hospital and sometimes requires intensive care.
Medications used to treat viral encephalitis include:
Many people who have viral brain infections recover completely. The chances of survival and recovery depend largely on the type of virus. Herpes encephalitis causes severe brain damage but can be treated with acyclovir. To ensure a good recovery, treatment must be given before the person lapses into a coma. Infants are more likely to have permanent damage. Young children tend to recover over a long period, while adults tend to recover quickly. The drug zidovudine (AZT) may slow dementia caused by the AlDS virus. Progressive multifocal leukoencephalopathy is sometimes treated with cytarabine or vidarabine, but at best these drugs only slow progression of the infection.
Although complementary and alternative therapies have not been extensively studied for the treatment of encephalitis, some studies indicate that , combined with proper medication, may aid in the healing process. Careful observation and supportive care, including rest, proper nutrition, and fluids are a mainstay of treatment for encephalitis and allow the body to fight the infection.
Although nutrition and dietary supplements have not been scientifically evaluated for use in treating encephalitis in humans, some studies suggest that melatonin may protect animals from serious complications associated with the condition and even increase their survival rates. In one study of mice that had been infected with Venezuelan equine encephalitis virus, melatonin supplements significantly reduced the presence of viruses in the blood and decreased the rate of death by more than 80%. More studies are needed, however, to determine whether similar treatment may offer the same protection to humans with viral encephalitis.
Animal studies suggest that Astragalus (Astragalus membranaceus), an herb used in Asia to improve weakness and to enhance immune function, may also protect humans from contracting viral encephalitis. In one study, mice that were given astragalus extracts before being infected with Japanese encephalitis virus, had a 60% to 80% chance of survival. Mice that did not receive astragalus extracts before being infected with the virus only had a 10% chance of survival. More studies are needed, however, to determine whether similar treatment may offer the same protection to humans with viral encephalitis.
Professional herbalists may also use a combination of herbs to relieve the symptoms associated with viral encephalitis, such as cognitive impairment, visual and speech disturbances, and difficulty performing routine functions. This herbal mixture includes:
A study of a small number of individuals with complications associated with encephalitis suggests that acupuncture delivered to the scalp may lessen the severity of such complications and reduce the symptoms associated with the condition. Some researchers theorize that scalp acupuncture is effective for individuals with encephalitis because all meridians converge at the head, and the method can stimulate and regulate qi throughout the entire body. More research is necessary, however, to conclusively determine whether scalp acupuncture is safe and effective for individuals with encephalitis.
Recently, behavioral and physical training techniques have been explored in the treatment of individuals recovering from encephalitis. In one case, a woman experiencing poor short-term memory and decreased muscle coordination as a result of viral encephalitis began to improve significantly after participating in a behavioral rehabilitation training program. As a result of the program, she gained a high level of independence and was able to return home from the hospital with only minimal assistance by a caregiver. More studies are needed to determine whether behavioral training is safe and effective for other individuals recovering from encephalitis.
Other ConsiderationsThe most common cause of encephalitis in newborns is vaginal delivery from a mother who is infected with herpes simplex virus 2 (HSV 2). This infection in newborns is often severe and fatal. For this reason, cesarean section may be advised for pregnant women with a history of HSV 2, even if there is no sign of an active infection.
Full recovery from encephalitis can take weeks or months, during which time many individuals experience complications ranging from fatigue and difficulty concentrating to tremors and personality changes.
The most severe complications associated with encephalitis result from the destruction of nerve cells in the brain that do not regenerate. The severity of complications depends on the condition of the immune system (whether it is healthy or weak) and the infection causing the encephalitis. For example, 80% of those infected with Eastern equine encephalitis, St. Louis encephalitis, and Japanese encephalitis, have permanent neurologic impairments (such as memory, speech, vision, hearing, muscle control, and sensation) and a very low survival rate, while those infected with EBV or Venezuelan equine encephalitis rarely experience any serious complications. The long-term outlook for those with HSV encephalitis depends primarily on how quickly the condition is treated.
Between 80% and 95% of individuals infected with viral encephalitis will survive the condition, but 20% will experience debilitating side effects or complications, such as memory loss or severe personality changes. The survival rate for those with HSV encephalitis increases dramatically from 30% to 70% when the condition is detected early and treated with antiviral medications.