Encephalitis - Causes, Symptoms and Treatment
What is Encephalitis?
A severe inflammation of the brain, encephalitis is usually caused by a mosquito-borne or (in some areas) a tick-borne virus. The virus may also be transmitted through ingestion of infected goat's milk and accidental injection or inhalation of the virus. In encephalitis, intense lymphocytic infiltration of brain tissues and the leptomeninges causes cerebral edema, degeneration of the brain's ganglion cells, and diffuse nerve cell destruction. Eastern equine encephalitis may produce permanent neurologic damage and is often fatal.
What are the Causes of Encephalitis?
Encephalitis generally results from infection with arboviruses specific to rural areas. In urban areas, it's most frequently caused by enteroviruses (coxsackievirus, poliovirus, and echovirus).
Other causes include herpesvirus,mumps virus, human immunodeficiency virus, adenoviruses, and demyelinating diseases following measles, varicella, rubella, or vaccination.
Between World War I and the Depression, a type of encephalitis known as lethargic encephalitis, von Economo's disease, or sleeping sickness occurred with some regularity. The causative virus was never clearly identified, and the disease is rare today. Even so, the term sleeping sickness persists and is often mistakenly used to describe other types of encephalitis as well.
The prognosis depends on factors such as immune status, pre-existing neurologic conditions, and extremes of age (very young or elderly) as well as the virulence of the virus.
What are the Signs and Symptoms of Encephalitis?
All viral forms of encephalitis have similar clinical features, although certain differences do occur.
Usually, the acute illness begins with sudden onset off ever, headache, and vomiting and progresses to include signs and symptoms of meningeal irritation (stiff neck and back) and neuronal damage (drowsiness, coma, paralysis, seizures, ataxia, and organic psychoses). After the acute phase of the illness, coma may persist for days or weeks.
The severity of arbovirus encephalitis may range from subclinical to rapidly fatal necrotizing disease. Herpes encephalitis also produces signs and symptoms that vary from subclinical to acute and often fatal fulminating disease. Associated effects include disturbances of taste or smell.
Diagnosis for Encephalitis
During an encephalitis epidemic, diagnosis is easily based on clinical findings and patient history. Sporadic cases are difficult to distinguish from other febrile illnesses, such as gastroenteritis and meningitis. When possible, identification of the virus in cerebrospinal fluid (CSF) or blood confirms the diagnosis.
The common viruses that also cause herpes, measles, and mumps are easier to identify than arboviruses. Arboviruses and herpes viruses can be isolated by inoculating young mice with specimens taken from patients. In herpes encephalitis, serologic studies may show rising titers of complement-fixing antibodies.
In all forms of encephal it is- CSF pressure which is elevated, and despite inflammation, the fluid is often clear. White blood cell and protein levels in CSF are slightly elevated, but the glucose level remains normal. An EEG reveals abnormalities. Occasionally, a computed tomographic scan may be ordered to rule out cerebral hematoma.
Treatment for Encephalitis
The antiviral agents acyclovir and foscarnet are effective only against herpes encephalitis. Treatment of all other forms of encephalilis is entirely supportive.
Drug therapy includes phenytoin or another anticonvulsant, usually given I.V.; glucocorticoids to reduce cerebral inflammation and edema; furosemide or mannitol to reduce cerebral swelling; sedatives for restlessness; and aspirin or acetaminophen to relieve headache and reduce fever.
Other supportive measures include adequate fluid and electrolyte intake to prevent dehydration and antibiotics for an associated infection such as pneumonia. Isolation is unnecessary.
Special Considerations and Prevention Tips for Encephalitis
During the acute phase of the illness:
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