Definition

Encephalitis is an inflammation of the brain, usually caused by a direct viral infection or a hypersensitivity reaction to a virus or foreign protein. Brain inflammation caused by a bacterial infection is sometimes called cerebritis. When both the brain and spinal cord are involved, the disorder is called encephalomyelitis

Description

Encephalitis is an inflammation of the brain that is a reaction of the body's immune system to infection or invasion. During the inflammation, the brain's tissues become swollen. The combination of the infection and the immune reaction to it can cause headache and a fever, as well as more severe symptoms in some cases.

The viruses causing primary encephalitis can be epidemic or sporadic. The poliovirus is an epidemic cause. Insect-borne viral encephalitis is responsible for most epidemic viral encephalitis. The viruses live in animal hosts and mosquitoes that transmit the disease. The most common form of non-epidemic or sporadic encephalitis is caused by the herpes simplex virus, type 1 (HSV-1) and has a high rate of death. Mumps is another example of a sporadic cause.

Causes

There are more than a dozen viruses that can cause encephalitis, spread by either human-to human contact or by animal bites. Encephalitis may occur with several common viral infections of childhood. Viruses and viral diseases that may cause encephalitis include:

·        ·        Chickenpox

·        ·        Measles

·        ·        Mumps

·        ·        HIV

·        ·        Herpes virus strains

·        ·        Polio

·        ·        Rabies

·        ·        Mosquito-borne viruses 

Primary encephalitis is caused by direct infection by the virus, while secondary encephalitis is due to a post-infectious immune reaction to viral infection elsewhere in the body. Secondary encephalitis may occur with measles, chickenpox, mumps, rubella, and EBV. In secondary encephalitis, symptoms usually begin 5-10 days.

Mosquitoes are carriers to many types of encephalitis including the Japanese type. The risk of contracting a mosquito-borne virus is greatest in mid- to late summer when mosquitoes are most active. The viruses responsible for this disease are classified as arbovirus and these diseases are collectively called arbovirus encephalitis.

Herpes simplex encephalitis is a disease responsible for 10% of all encephalitis cases and is the main cause of fatal encephalitis. In untreated patients, the rate of death is 70%.

Symptoms

Symptoms may progress rapidly, changing from mild to severe within several days or even several hours. The symptoms of encephalitis range from very mild to very severe and may include:

·        ·        Headache

·        ·        Fever

·        ·        Lethargy (sleepiness, decreased alertness, and fatigue)

·        ·        Malaise

·        ·        Nausea and vomiting

·        ·        Visual disturbances

·        ·        Tremor

·        ·        Decreased consciousness (drowsiness, confusion, delirium, unconsciousness)

·        ·        Stiff neck

·        ·        Seizures.

Diagnosis

Diagnosis of encephalitis includes careful questioning to determine possible exposure to viral sources. Tests that can help confirm the diagnosis and rule out other disorders include:

·        ·        Blood tests. These are to detect antibodies to viral antigens, and foreign proteins.

·        ·        Cerebrospinal fluid analysis (spinal tap). This detects viral antigens

·        ·        Electroencephalogram (EEG)

·        ·        CT and MRI scan.

·        ·        A brain biopsy (surgical gathering of a small tissue sample)

Treatment

Choice of treatment for encephalitis will depend on the cause. Bacterial encephalitis is treated with antibiotics. Viral encephalitis is usually treated with antiviral drugs including acyclovir, ganciclovir, foscarnet, ribovarin, and AZT. Viruses that respond to acyclovir include herpes simplex.

The symptoms of encephalitis may be treated with a number of different drugs. Corticosteroids are sometimes prescribed to reduce inflammation and brain swelling. Anticonvulsant drugs are used to control seizures. A person with encephalitis must be monitored carefully, since symptoms may change rapidly.

Prognosis

Encephalitis symptoms may last several weeks. Most cases of encephalitis are mild, and recovery is usually quick. Mild encephalitis usually leaves no residual neurological problems. Overall, approximately 10% of those with encephalitis die from their infections or complications such as secondary infection. Some forms of encephalitis have more severe courses, including herpes encephalitis, in which mortality is 15-20% with treatment, and 70-80% without. Antiviral treatment is ineffective for eastern equine encephalitis, and mortality is approximately 30%.

Permanent neurological consequences may follow recovery in some cases. Consequences may include personality changes, memory loss, language difficulties, seizures, and partial paralysis.

Prevention

Because encephalitis is due to infection, avoiding the infection may prevent it. Minimizing contact with others who have any of the viral illness listed above may reduce the chances of becoming infected. Most infections are spread by hand-to-hand or hand-to-mouth contact; frequent hand washing may reduce the likelihood of infection if contact cannot be avoided.

Mosquito-borne viruses may be avoided by preventing mosquito bites. Mosquitoes are most active at dawn and dusk, and are most common in moist areas with standing water. Minimizing exposed skin and use of mosquito repellents on other areas can reduce the chances of being bitten.

Vaccines are available against some viruses, including polio, herpes B, Japanese encephalitis, and equine encephalitis. Rabies vaccine is available for animals; it is also given to people after exposure.