Merck Manual

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Quick Facts

Overview of Brain Infections

By

The Manual's Editorial Staff

Last full review/revision Sep 2020| Content last modified Sep 2020
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Brain infections are very serious and can be fatal. They can be caused by:

  • Viruses (most common)

  • Bacteria

  • Fungi or parasites (rare)

Infections that involve only the brain are called encephalitis. Infections that involve the layers of tissue (meninges) that cover the brain and spinal cord are called meningitis. But encephalitis can spread and cause meningitis. And sometimes meningitis spreads to cause encephalitis.

Brain infections from a virus usually affect your whole brain. Brain infections caused by bacteria sometimes cause a pocket of pus, called a brain abscess.

How do infections get in your brain?

Infections usually start somewhere else. They can get to your brain and meninges in several ways:

  • From an infection nearby, such as in your teeth, sinuses, or ears

  • Through your blood from another part of your body

  • Directly from the outside, for example, through a skull fracture or during brain surgery

Infections that spread through your blood sometimes come from bug bites, particularly from mosquitoes and ticks.

What are the symptoms of brain infections?

Brain infections keep your brain from working properly. You often have:

  • Headache

  • Confusion and trouble thinking clearly

You may not act like yourself. Severe infections can cause seizures and make you go into a coma, have trouble breathing, and sometimes die.

How do doctors diagnose brain infections?

Doctors usually do:

How do doctors treat brain infections?

Doctors try to treat the cause of the infection. Antiviral drugs or antibiotics work for some infections but not all. Doctors also give medicine to relieve symptoms. If needed, they may put the person on a ventilator or give treatments to support the person's blood pressure.

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