How do infections affect the brain?

Brain infections exist, but an infection doesn’t have to start in the brain to affect it. Many viral, fungal and bacterial infections start elsewhere in the body and can spread to or somehow affect the brain. How the brain is affected depends on the type of infection.

Types of Infections

How infections affect the brain and the rest of the body depends on the type of infection. Infections are caused by: bacteria, viruses, fungi, or parasitesand the source of the infection can influence the symptoms.

For example, a viral or bacterial infection can cause a fever, but with bacterial infections, a fever is likely to reach much higher temperatures.

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HIV is the virus that causes AIDS. It attacks the immune system, making the person vulnerable to infections. But also HIV straight away affects the braininfects the cells that protect and support neurons and causes inflammation.

These changes can cause confusion, forgetfulness, mood disturbances, headaches and movement problems. Some studies also show that HIV can shrink certain brain structures and affect information processing.

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Strep A

Group A streptococci cause a range of infections, from strep throat to rheumatic fever to toxic shock syndrome. studies show that recurrent streptococcal infections can affect the brain, especially in children.

Strep A has molecules in its bacterial cell wall that are similar to those found in brain tissue. The body recognizes these molecules and instead of attacking them, it reacts protectively and attacks the tissue that houses the virus. These cells can then enter the brain through the nasal cavity and travel to the part of the brain responsible for our sense of smell. Once in the brain, they break the blood-brain barrier so that other cells can invade, leading to inflammation.

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Herpes Simplex 1

Herpes simplex 1 (HSV-1) is a virus that causes cold sores and genital herpes† In rare cases, after the initial infection, the virus reaches the central nervous system and replicates, causing inflammation and encephalitis.

Interestingly, HSV-1 encephalitis has been associated with the accumulation of Alzheimer’s disease biomarkers.

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Cytomegalovirus or CMV belongs to the same family of viruses that cause cold sores and chickenpox. Most people with a CMV infection have no or mild symptoms, but people with compromised immune systems may have a more serious infection that affects the nervous system, including the brain

It can cause inflammation in the brain and spinal cord, and unborn babies whose mothers have CMV infections are at increased risk for hearing loss, seizures and visual disturbances at birth.

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Unlike most infections, rabies travels directly from the point of entry, usually an animal bite, nasty the brain† This process can take up to ten days, depending on the site of the bite. Once it reaches the brain, the virus begins to multiply and the disease is usually fatal.

Early symptoms are headache and fever, but once the infection reaches the brain, symptoms include hallucinations, confusion, agitation. As the infection spreads through the brain, the person may experience seizures, paralysis, coma, or death.

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Meningitis is a infection by the liner of the spinal cord and brain. This infection causes these membranes to swell and press against the brain and spinal cord, causing life-threatening complications. Symptoms, such as headache, high fever, and confusion, often come on suddenly and worsen quickly.

Many bacteria and viruses can cause meningitis. Viral meningitis is more common, but bacterial meningitis is more serious and can lead to stroke, paralysis, or brain damage. When detected and treated early, many people recover from meningitis without lasting damage. But even with prompt and effective treatment, this infection can lead to brain damage, hearing loss, seizures and permanent disabilities.

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Brain abscesses

Infections of the middle ear, sinuses, or mastoid cells in the temporal bones of the face can spread to the brain and brain abscess† Brain trauma or brain surgery can also cause these growths.

A brain abscess is a pocket filled with infected material or pus. It can cause swelling or cut off blood flow to parts of the brain and is a medical emergency. Signs of a brain abscess include fever, nausea, vomiting, confusion, weakness on one side of the body, and pain in the neck or back.

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COVID-19 has a wide range of symptoms that affect different parts of the body, including the brain† Studies show that 80 percent of people hospitalized with COVID-19 had some sort of neurological symptoms, including loss of taste and smell, brain damage, difficulty remembering words, coma and stroke.

Researchers also found that people with pre-existing neurological conditions, such as nervous disorders, dementia and chronic migraines, were more likely to experience neurological symptoms with a COVID-19 infection.

Woman sniffs the smell of coffee from the cup while preparing a drink in the kitchen in the morning NataBene/Getty Images

Infection and the blood-brain barrier

The blood-brain barrier is the microvasculature of the central nervous system. It has special properties that tightly regulate the movement of cells, molecules and ions in and out of the brain to maintain balance and keep out toxins, diseases and pathogens.

Systemic infection and inflammation can break this barrier, to make it is more permeable† While this may explain why so many infections affect the brain, researchers are also interested in whether they can use this permeability therapeutically, pointing to hope for future treatment of many conditions.

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