How Serious Is Encephalitis?

All cases of encephalitis should be considered a medical emergency.

The severity of the illness varies a great deal. Some cases are mild, and full recovery follows in a week or two. Other cases may be severe with permanent effects or even death.

One of the most dangerous types is measles encephalitis, which can follow a bout with measles and has a death rate approaching 50%. Survivors are likely to have lasting effects like learning difficulties or a physical handicap. Luckily, it is preventable by the common measles vaccination.

Encephalitis due to herpes virus may be serious. When it is passed on to a newborn, it often leaves the baby with neurological damage and is fatal in many instances.

Of the illnesses caused by arboviruses, the most serious are Western equine encephalitis, found mostly in the western U.S. and Canada, and Eastern equine encephalitis, seen mostly in the Atlantic and Gulf Coast regions of the U.S. During outbreaks of Eastern equine encephalitis, as many as 70% of those affected die, and survivors often have permanent brain or nervous system damage.

Western equine encephalitis is most severe in young children and causes seizures in 90% of infants. Half of them will have permanent brain damage.

Other types of encephalitis, such as St. Louis encephalitis and those caused by enteroviruses, are less deadly but can still have serious lasting effects. They include seizures (which can be controlled with anti-convulsant medicines), weakness in a part of the body, partial hearing or vision loss, and a slight alteration of personality. Many problems improve over time but, in some cases, they can be permanent.

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