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Symptoms and Signs of Brain Infection

Doctor's Notes on Brain Infection

A brain infection is a bacterial, viral, fungal, or parasitic infection of the tissue of the brain itself or the membranes surrounding the brain and spinal cord (meninges). Bacteria and viruses are the most common causes of brain infections. An abscess is a localized collection of infectious organisms that can also occur in the brain.

Signs and symptoms of a brain infection depend to some extent on the type of infection. Viral meningitis usually causes much milder symptoms than bacterial meningitis, which can be fatal. Symptoms associated with bacterial meningitis can include severe headache, neck stiffness, high fever, nausea, vomiting, pain or discomfort when looking at bright lights, sleepiness, and confusion. Affected infants may be fussy, irritable, and feed poorly.

Medical Author:
Medically Reviewed on 3/11/2019

Brain Infection Symptoms

Various types of brain infections lead to many different symptoms, which can depend on the age of the person, the type of bacteria, the type of infection, and the acuteness of the disease.

  • In general, people older than 2 years of age with acute bacterial infection develop high fever, severe headache, stiff neck, nausea, vomiting, discomfort when looking into a bright light, sleepiness, and confusion.
  • Newborns and infants can be unusually fussy, irritable, and sleepy. They may feed poorly and not be comforted by holding. Seizures can be a late development of the disease.
  • Severe forms of bacterial meningitis, particularly meningococcal, can cause shock with complete loss of consciousness and coma and bring about a spreading purplish rash. An infant can have bulging fontanelles (soft spots) on the head and have a decreased muscle tone in arms and legs.
  • Someone with viral brain infections tends to appear somewhat less ill. Flu-like symptoms in addition to mild signs and symptoms outlined for each condition may be seen.

Brain Infection Causes

Causes of bacterial meningitis: Three types of bacteria are the most common causes of meningitis in all age groups except newborns:

The introduction of Hib vaccine as part of routine pediatric immunization has significantly reduced the occurrence of serious Hib disease. Newborns are usually infected with coliform bacteria (bacteria in the gut, contracted at birth) such as Escherichia coli or Listeria.

  • How organisms are transmitted: Unlike the flu or the common cold, which can be transmitted by casual contact or by simply breathing the air in the same room with an infected person, most of the bacteria causing meningitis are not very contagious. It would take the exchange of respiratory and throat secretions, from coughing, sneezing, or kissing, to spread the bacteria. The only exception is meningococcal meningitis. Anyone in the same household, or who had a prolonged contact, or was in direct contact with a person's oral secretions would be considered at increased risk of contracting the infection. People who have been exposed in this manner should receive preventive antibiotics.
  • Those most at risk: Anyone can get bacterial meningitis. It most commonly affects infants and small children. Anyone who had close or prolonged contact with a person affected by certain bacteria (such as N. meningitidis or Hib) are also at increased risk. This includes day-care workers, military recruits, jail cellmates, and anyone directly exposed to discharges from the mouth or nose of an infected person. The other groups at risk include people with weakened immune systems, diabetics, chronic alcoholics, IV drug abusers, and anyone older than 60 years of age.
  • The following are other common brain infections:
    • Toxoplasmosis (also known as toxo) is caused by the parasite Toxoplasma gondii. Infection is acquired, for example, from an infected mother to an unborn baby, by eating unwashed vegetables or undercooked meat, or by direct contact with cat feces (the cat is a host for this organism). The symptoms are similar to a mild form of bacterial meningitis. People at risk are pregnant women and those with weakened immune systems, such as people who are HIV positive. Prognosis is poor for infections transmitted from mother to newborn. More than 50% of affected infants die within a few weeks after birth. The disease also is severe in someone with a weakened immune system, and aggressive treatment with medications is used. Frequently, death results.
    • Cerebral cysticercosis is caused by the pork tapeworm. The infestation is acquired when people eat food contaminated by feces containing tapeworm eggs. This disease has recently become relatively common in the southwestern U.S. Depending on the stage of the disease, symptoms could be those of a mild form of meningitis, or more severe form, or even cause sudden death. The most common symptoms are seizures. Few medications can stop the progression of the disease. However, once the cerebral form is acquired, treatment is usually given to relieve the symptoms.
    • Trichinosis is caused by the roundworm Trichinella spiralis. It is acquired by eating larvae in raw or undercooked pork and some other wild meats, including bear, moose, and wild boar. An infected person may have symptoms similar to encephalitis with confusion and delirium. Coma, seizures, paralysis, and other signs of neurologic loss are found in more severe forms. Most people recover within a few days or weeks without any long-term problems. The treatment is usually directed at symptom relief.
    • One of the most common infections transmitted by insects in the U.S. is Lyme disease. It is caused by the bacterium Borrelia burgdorferi, which infects and multiplies inside of ticks of the Ixodes species. Then it is transmitted to humans by the tick bite. If remained untreated, the disease can have serious complications, which include various neurologic problems. The most common neurologic complication is facial seventh nerve palsy (Bell's palsy, presenting as a facial droop) or damage to other facial nerves, and inflammatory radiculopathy (compression of nerve roots in the spine), which appears as tingling, burning pain, or numbness in an extremity. Although rare, the most concerning neurologic complication of late Lyme disease is meningitis, with its typical symptoms and signs. A small percentage of the patients with untreated Lyme disease and neurologic complications developed short-term memory problems and other cognitive deficits. Early treatment with antibiotics is advised when Lyme disease is suspected.
    • Coccidioidal meningitis is a severe complication of coccidiomycosis (valley fever), a common fungal infection in the southwestern U.S. The primary disease is caused by the inhalation of the Coccidioides soil fungal spores, leading to predominantly respiratory symptoms. Once the infection spreads to other organs via the bloodstream, almost half of those affected develop meningitis. The meningitis, in addition to the typical signs and symptoms, is most commonly complicated by the presence of a hydrocephalus, which is the abnormal accumulation of cerebrospinal fluid (CSF, fluid that bathes the brain and spinal cord) in the ventricles of the brain. Additionally, the inflammatory changes of the brain and its great vessels could cause symptoms similar to those of a stroke. The treatment of this condition is very complex, with both intravenous antifungal therapy and occasional direct infusion of the medication in fluids bathing the brain and spinal cords. The hydrocephalus frequently requires the placement of a ventriculoperitoneal shunt (which drains the extra CSF directly from the brain ventricles into the abdominal cavity). Despite all the technological and pharmacological developments in recent years, the prognosis for this condition remains poor.
    • An uncommon causative agent of meningitis, affecting almost exclusively immunocompromised people, is a fungus from the Cryptococcus family. This ubiquitous fungus thrives in soil and in the debris around tree bases, with a particular predilection for bird droppings. The usual mode of transmission is the inhalation of the fungal spores in soil, with subsequent spread through the bloodstream to the CNS. Cryptococcal CNS infection causes the typical symptoms and signs of meningitis. If left untreated, the patient has severe complications with permanent brain damage, hearing loss, and coma. In patients with severe immunodeficiency, the untreated disease is invariably fatal. The usual treatment is in-hospital long-term infusion of intravenous antifungal drugs. All people at risk should avoid bird droppings and any outside activities, including digging and working with soil.
    • Tuberculosis, caused by Mycobacterium tuberculosis, can spread through the lymphatic system to the CNS. The resulting meningitis, has a short initial period with symptoms of upper respiratory infection, followed by the onset of various neurologic deficits, such as visual impairment, focal weakness and numbness, and unstable gait with paralysis. The treatment is the same as for tuberculosis, with a multidrug regimen and symptomatic management in a hospital. Some studies suggested that BCG vaccination offers significant protection against tuberculous meningitis and should be strongly considered in people with high risk of contracting this disease.
    • Cerebral abscess is often a complication of chronic sinus or middle-ear infections or the distant spread of the infection from somewhere else (such as a lung abscess or pneumonia). It can also be a consequence of head trauma or a neurosurgical procedure. The symptoms depend on the location of the abscess, but almost all people with this condition have a severe headache, fever, or generalized malaise. Treatment includes IV antibiotics and frequently surgical drainage.
  • Spinal abscess is caused by various bacteria. Most commonly, infection spreads to the spinal canal directly from any inflammation near the spine, such as certain ulcers or large and deep skin abscesses, extension from the GI tract, or from a source of infection elsewhere in the body. Groups at risk include IV drug users, people with diabetes, or anyone on therapy with a weakened immune system. The spinal abscess usually develops suddenly, with fever, back pain, redness, and swelling of the affected area. Without treatment, muscular weakness and paralysis of the extremities may develop. Treatment includes surgical drainage and extensive use of IV antibiotics in the hospital.
  • The West Nile virus and other members of the encephalitis-causing virus family (St. Louis encephalitis, western equine and eastern equine encephalitis, and La Crosse encephalitis) are usually spread by bites of ticks, mosquitoes, and flies. Specifically, the West Nile-transmitting vector is the mosquito, feeding on infected birds (which serve as a natural reservoir), and then passing the infected blood to humans. The virus itself, as well as the host's immune response, disrupt normal function of nerve cells, especially in the gray matter of the brain. This leads to various cognitive and psychiatric signs including confusion, lethargy, problems with coordination, and possible seizures. Very common symptoms of the infected person, especially with West Nile infection, are headaches, fever, nausea, vomiting, and photophobia (sensitivity to light). Most of the infections have a mild course with a favorable prognosis; however, the patients with more severe degree of infection may develop altered mental status, very high fever, neck stiffness, and seizures. Rarely, especially in very old and immunocompromised patients, the disease progresses to full-blown encephalitis, with subsequent coma, stupor, and death. Unfortunately, there is no specific treatment for this type of viral infection. All patients should get supportive therapy for symptom relief. Preventive measures include the liberal use of insect repellants when spending time outdoors in endemic areas.
  • The members of herpes virus family (herpes simplex types 1 and 2, varicella zoster, Epstein-Barr, as well as cytomegalovirus) can enter the central nervous system from the peripheral nervous system (along the nerves outside of the brain and spinal cord), where they reside, and cause severe illness such as fulminant meningitis, encephalitis, or myelitis. These infections are particularly deadly in immunocompromised patients. The clinical presentation is usually typical for CNS infection, with headaches, lethargy, nausea, vomiting, and neck stiffness. The signs and symptoms of specific infection can include psychiatric features and multiple seizures in herpes simplex 1, radicular symptoms (compression of nerve roots at the spinal column; numbness and tingling of the arms or legs) with urinary retention in herpes simplex type 2; and blindness from cytomegalovirus infection in severely immunocompromised patients. The Epstein-Barr virus CNS infection is a very strong risk factor for developing multiple sclerosis in the future. Unlike most of the other viral CNS infections, there are multiple effective antiviral medications available to treat these potentially deadly infections.
  • Poliomyelitis (polio) is caused by a small poliovirus. The spread to the nervous system occurs when orally ingested virus multiplies in the digestive system, then gets into the bloodstream, and eventually enters the central nervous system. The disease progressively worsens and eventually leads to paralysis, coma, and arrest of the respiratory and cardiac muscle. Since the advent of the polio vaccine, the incidence of this disease has decreased dramatically in most of the developed countries. In the U.S., it is limited to a few isolated cases imported from overseas. The last naturally occurring case of wild polio in the U.S. was in 1979. The vaccination includes three doses of vaccine within the first year of life, which would give a lifelong immunity. Infants with weak immune systems are at risk for contracting polio through immunization, but the risk is extremely small.
  • Rubella (German measles) is caused by the rubella virus. The consequences of this disease, affecting the unborn fetus infected during the first trimester of pregnancy, can be devastating. The baby may be born with a variety of defects including deafness, cognitive dysfunction, and heart problems. At birth, the infant has a meningitis-like illness and usually is lethargic and inactive. The proper immunization of the mother, with a series of vaccinations given throughout adolescence and early adulthood, prevents a woman from getting rubella, which is especially important during pregnancy.
  • Mumps and measles are both caused by viruses. Young children are most commonly affected. Transmission occurs through the respiratory routes. Complications may include viral meningitis or encephalitis in varying degrees of severity. The most common complications of mumps and measles are deafness and seizures, respectively. Prevention is attained through adequate childhood immunization.
  • Rabies is another viral infection. It is transmitted to humans by the bite of an infected animal or, in rare instances, by an inhalation of airborne viral particles in bat-infested caves or by laboratory workers. Worldwide, the disease is commonly caused by the bite of a rabid dog but also might be transmitted by cats, raccoons, skunks, foxes, wolves, and many other domestic and wild animals. Despite popular belief, no transmission has occurred from the bites of mice, rats, or rabbits. The disease is rare in the U.S., where we have tight control of rabid animals. The virus causes a severe form of encephalitis and myelitis. It may cause initial flu-like symptoms, very high fever (up to 107 F), extreme restlessness, hypersensitivity to touch, general convulsions, total body paralysis, bizarre hallucinations, excessive flow of saliva, absolute refusal to drink any fluids, with gradual paralysis, coma, and almost invariably death. There is no specific antiviral therapy available, but postexposure immune globulin and immunization are very effective and widely available.
  • AIDS and HIV encephalitis (also known as AIDS dementia) is caused by the human immunodeficiency virus (HIV). HIV can directly infect the central nervous system, causing a range of neurologic conditions. The most common is so-called AIDS dementia. It is characterized by the slow onset of behavioral, intellectual, and motor impairment. Early symptoms include confusion, loss of libido, social withdrawal, decreased concentration, poor balance, and weakness. Psychiatric problems are common. In the late stage, severe dementia, inability to control urine flow, and an inability to speak and walk may occur. The treatment includes standard antiretroviral drugs for HIV with variable results.
  • Infection with Zika virus has been in the recent news due to a significant increase in the birth of babies with head deformities (microcephaly) and various neurologic complications born to mothers infected with this virus. There is still an ongoing debate about the causal link between the infection of the pregnant woman and this devastating adverse pregnancy complication and outcome. Zika virus is transmitted to humans by the bite of an infected mosquito, with the majority of cases occurring in South and Central America. The illness has a very mild course in most cases, with a fine rash as the most common presenting sign, as well as some other symptoms such as low-grade fever, headache, muscle and joint aches, and pink or reddened eyes. The disease is usually self-limiting, with most patients recovering fully in a few days.
  • Very few patients infected withZika virus develop a rare late neurologic complication known as a Guillain-Barré syndrome. This potentially fatal condition is triggered by a severe autoimmune reaction to the central and peripheral nervous system. It is characterized by progressively worsening weakness and paralysis of the muscles of the entire body, painful sensations in the extremities, and involvement of the nerves that supply the head and neck. All patients diagnosed with Guillain-Barré syndrome are admitted to the hospital for observation and management of symptoms, since there is no specific medication or treatment for this condition. Most patients will have a complete recovery, with very few remaining with debilitating residual neurologic symptoms.

Bacterial Infections 101 Types, Symptoms, and Treatments Slideshow

Bacterial Infections 101 Types, Symptoms, and Treatments Slideshow

Bacteria are microscopic, single-cell organisms that live almost everywhere. Bacteria live in every climate and location on earth. Some are airborne while others live in water or soil. Bacteria live on and inside plants, animals, and people. The word "bacteria" has a negative connotation, but bacteria actually perform many vital functions for organisms and in the environment. For example, plants need bacteria in the soil in order to grow.

The vast majority of bacteria are harmless to people and some strains are even beneficial. In the human gastrointestinal tract, good bacteria aid in digestion and produce vitamins. They also help with immunity, making the body less hospitable to bad bacteria and other harmful pathogens. When considering all the strains of bacteria that exist, relatively few are capable of making people sick.


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.