What Is a Brain Infection?

A brain infection can occur as a result of a virus, bacteria, fungus, or parasite. It often involves other parts of the central nervous system (CNS) as well, including the spinal cord. There are several types of brain infections, each of which strikes different areas:

• Encephalitis, inflammation of the brain
• Meningitis, inflammation of the lining of the brain and spinal cord (the meninges)
• Traverse myelitis, inflammation of the spinal cord
• Cerebral abscess, a pocket of pus in the brain

Inflammation, the body's natural response to infection, can trigger both physical and neurological symptoms due to the swelling of the brain or spinal cord. Abscesses pose harm by placing pressure on the functional tissues of the brain, called the parenchyma.

This article explores four common types of brain infections, including their causes and symptoms. It also explains how brain infections are diagnosed, treated, and prevented.

Types of Brain Infections

The different types of brain infections vary by cause and location. Some like encephalitis affect the entire brain, while others are localized to one area of the brain, such as an abscess. However, each type of brain infection requires treatment right away. 

Encephalitis

Encephalitis is usually caused by a virus, such as the herpes simplex virus types 1 and 2, or arboviruses, in the United States. Arboviruses are spread from animals to humans and causes mosquito-borne disease. An example is the West Nile virus.

Symptoms may start out as mild flu-like symptoms and headaches, quickly followed by behavioral changes, hallucinations, and confusion.  

Meningitis

Meningitis can be caused by a virus or bacteria. Bacterial meningitis is a serious condition and needs to be treated immediately. Rarely, meningitis can also be caused by a fungus or parasite. 

Several types of bacteria can first cause an upper respiratory tract infection and then travel through the bloodstream to the brain. Bacterial meningitis can also occur when certain bacteria invade the meninges directly.

The classic signs of meningitis include a sudden fever, severe headache, stiff neck, photophobia, and nausea and vomiting. Being unable to bend your chin down to your chest is a sign of meningitis. While the symptoms may start out resembling those of a cold or upper respiratory infection, they can quickly become more severe. 

Traverse Myelitis

The spinal cord is responsible for carrying sensory information back to the brain and motor messages from the brain to the body. When it is inflamed like in the case of traverse myelitis, symptoms can include pain, weakness in the limbs, bowel and bladder problems, and sensory problems. Many people with myelitis also experience muscle spasms, headache, fever, and loss of appetite. 

Myelitis may be related to an immune disorder or infection from a virus, bacterium, fungus, or parasite. Most people who experience myelitis make a full recovery, but the process can take months to years. There is no cure for myelitis, but the symptoms can be treated. 

Cerebral Abscess

A cerebral abscess, also known as a brain abscess, occurs when a collection of pus becomes enclosed in brain tissue. This rare condition can be caused by a bacterial or fungal infection, and is also a possible complication of surgery or trauma. People with compromised immune systems are more at risk of having a brain abscess. 

Symptoms include a high fever, severe headache, behavior changes, and nausea and vomiting. Over time, an abscess can cause changes in speech, motor weakness, spasticity, and seizures. Once it is discovered, an abscess must be located and surgically drained, followed by four to eight weeks of antibiotic therapy. 

Causes

There are several types of causes of brain infections, and each one has its own transmission route. Viruses may be spread through close contact or respiratory secretions, such as sharing drinking glasses or kissing. Bacterial infections can also be spread through close contact or contaminated food preparation. 

Here's a breakdown of all possible causes of brain infections:

• Virus: While rare, several viruses can lead to an infection of the brain, spinal cord, or surrounding area. Possible causes include the herpes simplex virus, varicella zoster virus, cytomegalovirus, Epstein-Barr virus, and influenza viruses. Mosquito-borne illnesses like West Nile and Zika may also lead to a brain infection.
• Bacteria: The bacteria most likely to lead to a bacterial brain infection in the United States include Streptococcus pneumoniae, group B Streptococcus, Neisseria meningitidis, Haemophilus influenzae ,and Listeria monocytogenes.
• Fungus: A fungal infection that spreads to the brain may be caused by the Aspergillus, Blastomyces, Coccidioides, or Cryptococcus fungus.
• Parasite: A parasitic infection in the brain may be caused by toxoplasmosis, cysticercosis, schistosomiasis, or strongyloides. 
• Immune system disorders: If you have a compromised immune system for any reason, you may be more at risk of experiencing a brain infection. People with an HIV infection are more at risk of rare infections such as a brain abscess. Multiple sclerosis may also lead to myelitis. 

Symptoms

The symptoms of a brain infection will depend on the area of the brain that has been infected, as well as the severity of the infection. 

The symptoms for each type of brain infection vary as follows:

• Meningitis: Sudden fever, severe headache, stiff neck, photophobia, and nausea and vomiting
• Encephalitis: Headache, behavioral changes, hallucinations, altered level of consciousness
• Myelitis: Weakness of the arms and legs, shooting pain, numbness and tingling, bowel and bladder dysfunction
• Abscess: High fever, severe headache, behavior changes, and nausea and vomiting

Diagnosis

The diagnostic tool used to diagnose your brain infection will depend on your symptoms and physical exam findings. Any symptoms of a brain infection should be evaluated by a healthcare provider right away. If you are concerned about a brain infection, your doctor will perform a neurological exam to evaluate your motor and sensory function. 

After taking a thorough history and performing a physical exam, your healthcare provider may recommend the following tests: 

• Imaging studies: Imaging studies are used to detect inflammation or lesions in the brain or spinal cord. A brain MRI can detect an abscess or lesion, as well as an underlying condition that could be causing the symptoms, such as multiple sclerosis. A brain CT scan may be used to detect inflammation. 
• Blood cultures: If a bacterial infection is suspected, blood cultures will be drawn to determine the specific type of bacteria causing the infection. This information will then be used to select the most effective antibiotic medication. 
• Lumbar puncture: A lumbar puncture, also called a spinal tap, involves inserting a needle in between the vertebrae in the lower back to remove cerebrospinal fluid, which flows through the brain and spinal cord. This fluid may be tested for bacteria, proteins, or increased white blood cells. 

Treatment

Treatment for a brain infection depends on which type of infection you have. However, early treatment is essential for minimizing complications and dangerous symptoms, so never hesitate to see your healthcare provider if you are concerned. 

Therapies used to treat a brain infection can include the following:

• Antibiotics are started right away if a bacterial infection is suspected. If you are being evaluated for meningitis, your medical team will most likely start IV antibiotics while waiting for test results. 
• Corticosteroids are usually prescribed to help lower inflammation in the brain or spinal cord. Most brain infections involve some degree of inflammation, which can put pressure on the brain and spinal cord and lead to serious complications. A corticosteroid may help reduce swelling and immune system activity.
• Antiviral medications are prescribed when the medical team suspects that your brain infection is caused by a virus. If you present with symptoms of encephalitis, an antiviral drug is usually prescribed right away.

Prognosis

The prognosis for a brain infection depends on the severity of your condition, what caused the infection, and how fast treatment was initiated. Most people who experience a brain infection make a full recovery.

The following treatments may be needed for long-term recovery:

• Physical therapy
• Occupational therapy
• Psychotherapy 

Recovery from an infection of the brain will vary depending on the degree of brain inflammation. In some cases, inflammation of the brain can lead to coma and death.

Survival and Mortality

The risk of death (mortality) can vary by both the location of the infection, the type of infection and other factors:

• Encephalitis: Between 5% of 20% of people hospitalized for encephalitis die in the hospital irrespective of the infection type.
• Meningitis: Streptococcus pneumonia, the most frequent cause of bacterial meningitis, is associated with a 17% risk of mortality among hospitalized people.
• Traverse myelitis: Studies vary, but some suggest that the median survival time from the time of diagnosis is 8.9 years, with some people living up to 16 years. Older age and tobacco use contribute to shorter survival times.
• Cerebral abscess: Again, studies vary, but most suggest that the in-hospital death rate among people with a brain abscess hovers at around 16%. Cases commonly involve Streptococcus bacteria.
  

Prevention

A brain infection cannot always be prevented, but one effective step to take is to get vaccinated. Many causes of bacterial brain infections are now preventable with the following vaccines:

• Meningococcal vaccines help protect against N. meningitidis
• Pneumococcal vaccines help protect against S. pneumoniae
• Hib vaccines help protect against Hib

To prevent viral and bacterial infections that can spread to the brain, take regular safety precautions like washing your hands and avoiding contact with individuals who are ill.

To protect yourself against mosquito- or tick-borne illnesses that could lead to a brain infection, use insect repellent when spending time outdoors and opt for long sleeves and pants. Aim to limit your outdoor activities at night when mosquitoes are more active and address any standing water around your home.

Summary

If you have symptoms of a brain infection, talk to your healthcare provider or get emergency medical help immediately. Left untreated, a brain infection can cause serious complications.

A Word From Verywell

A brain infection is a serious condition that can quickly become life-threatening if left untreated. Learning what signs to look out for can help you prepare and get help right away if you do become infected. Be on the lookout, especially if you have a condition that places you at higher risk of a brain infection.

If you or a loved one believe you are experiencing the symptoms of a brain infection, see your healthcare provider or seek emergency medical help right away. Early treatment is crucial, and remember that most people who are treated right away make a full recovery.