Chapter 19


Infectious Diseases Affecting the Nervous System




  Inflammation of the meninges characterized by headache, stiff neck, vomiting, and fever

  Bacterial meningitis - a more serious form usually associated with a previous viral infection




Meningitis: Causes

  Neisseria meningitidis (Meningococcal)

  Can result in shock and death within 24 hours after infection

  Associated with epidemics; most cases are in young children

  Meningitis symptoms are accompanied by purplish spots on the skin called petechiae

  Virulence factors include IgA protease and a capsule to avoid phagocytosis

  Endotoxin released in the bloodstream causes a drop in blood pressure leading to shock

  Transmitted by respiratory droplets or secretions

  Polysaccharide conjugate vaccine available or antibiotic prophylaxis


  Streptococcus pneumoniae (Pneumococcal)

  Leading cause of community-acquired meningitis

  Usually preceded by otitis media, sinusitis, or pneumonia; If not treated, can lead to coma

  Virulence factors include alpha-hemolysin and capsule to protect from phagocytosis

  Polysaccharide conjugate vaccine available or antibiotics

Prevnar for children; Pneumovax for adults


  Haemophilus influenza

  was a common cause of severe meningitis and death before vaccine was introduced

  conjugate polysaccharide vaccine available or antibiotic prophylaxis


  Listeria monocytogenes  (Listeriosis)

  Foodborne disease commonly contracted from eating nonpasteurized dairy products or contaminated poultry and meat

  The bacteria penetrate the intestinal linings and enter the bloodstream, then cross over into the cerebrospinal fluids where they infect the meninges

  Usually a mild disease in healthy adults, but causes meningitis in elderly, immunocompromised, or very young

  Bacteria easily transmitted to babies through the placenta or birth canal

  The organism can grow in commercially prepared foods at refrigerator temperatures

resistant to cold, heat, salt, pH extremes, and bile

  Treated with antibiotics early


  Cryptococcus neoformans

  Opportunistic fungal infection acquired by inhalation of dust laden with pigeon droppings

  Rarely invades the nervous system of healthy people, but can be fatal in patients with diabetes, cancer, and immunodeficiency

highest rates of disease are among AIDS patients

  Causes confusion, dizziness, headache, vomiting, weight loss, paralysis, seizures, coma

  No person to person transmission

  Treat with anti-fungals for several weeks


  Coccidioides immitis  (Coccidioidomycosis)

  Systemic fungal infection caused by inhalation of spores

  Prevalent in dry, semi-arid desert areas in the southwestern US

  Begins as a respiratory infection, but quickly disseminates through the body, especially in immunocompromised

affects meninges, bone, and skin

  Treat with anti-fungal medications


  Viral meningitis

  Also called Aseptic Meningitis because no bacteria or fungi are found in the cerebrospinal fluid (CSF)

  Much more common than bacterial meningitis, it causes much milder symptoms with recovery in 7 to 10 days

  Most cases are caused by enteroviruses and occur in children   


  Neonatal meningitis

  Streptococcus agalactiae

group B strep that colonizes 10-30% of female genital tracts and is most frequent cause of neonatal meningitis

  Escherichia coli K1

serious disease in premature babies; transmitted through birth canal

  Cronobacter sakazakii

environmental bacteria transmitted through contaminated powdered infant formula





  Naegleria fowleri protozoan acquired from swimming in warm, natural bodies of fresh water

  Amoebas enter nasal passages and migrate to brain

  Primary amoebic meningoencephalitis (PAM) rapid, massive destruction of brain and spinal tissue

causes hemorrhage, coma, and death within a week

  Treat immediately with anti-protozoan drugs

  Acanthamoeba protozoan acquired from swimming in warm waters; invades broken skin or eye

  Granulomatous amoebic meningoencephalitis (GAM) similar to Naegleria, but course of infection is longer




Acute Encephalitis

  Most cases are caused by viruses

  Viral encephalitis is much more likely to cause death or permanent disability than viral meningitis

  Same onset as meningitis, but can lead to epilepsy, paralysis, tremor, deafness, blindness, seizures, or coma    

  Can be sporadic (a few widely scattered cases all the time) or it can be epidemic

  Epidemic encephilitis - caused by Arboviruses (arthropod-borne)

  Most are transmitted by mosquitos

  Virus is released into tissues through a bite, replicates in lymphatic tissues, and then migrates to the brain, causing swelling and damage to brain, nerves, and meninges

  No treatment exists, but live attenuated vaccines are available for some

  Western Equine Encephalitis (WEE)

  Eastern Equine Encephalitis (EEE)

  LaCrosse Encephalitis

  St. Louis Encephalitis (SLE)

  West Nile Encephalitis

  Sporadic encephalitis - usually due to herpes simplex viruses, JC virus, or measles virus




Subacute Encephalitis

  Symptoms take longer to show up and are less striking


  Caused by the protozoan Toxoplasma gondii

  Can infect many species but cats are the primary host

  Transmitted by inhalation of oocysts in cat feces or ingestion of contaminated meats

  Oocysts are ingested by rodents or birds, which are then eaten by cats and released in feces to complete the cycle

  Mostly asymptomatic or mild symptoms, but can be fatal in immunocompromised individuals

produces brain lesions and fatal disruptions of the heart and lungs

  Congenital transmission can result in stillbirth or severe abnormalities

  Treated with anti-protozoan drugs for long periods


  Transmissible Spongiform Encephalopathies

  Chronic degenerative brain diseases of animals and humans caused by prions

  prions are misfolded forms of normal cell proteins (PrP) that are toxic to neurons

  Abnormal PrP can spontaneously convert other normal PrP to the abnormal form

  Prions are resistant to chemicals, radiation, and heat

  Accumulation of abnormal PrP causes death of neurons, giving brain tissue a spongy appearance

  Human diseases include: Creutzfeld-Jacob disease (CJD), Gerstmann-Strussler-Scheinker disease, and fatal familial insomnia

  Symptoms include altered behavior, dementia, impaired senses, delirium, premature senility, and uncontrollable muscle contractions

  Other diseases include scrapie, transmissable mink encephalopathy, and bovine spongiform encephalopathy (mad cow disease)

  CJD can be inherited or acquired from exposure to infected brain tissue or blood

  No known treatment; usually ends in death within a year




  A slow progressive zoonotic disease characterized by fatal encephalitis

  Caused by the Rabies virus

  The virus is spread to humans from wild and domestic reservoirs via bites, scratches, and sometimes inhalation of respiratory droplets

  The virus initially stays at the entry site and multiplies before moving along sensory nerves to the CNS

  Viral replication in the CNS is followed by migration to structures such as the eye, heart, skin, and salivary glands

  Prodromal phase - characterized by non-specific flu-like symptoms

  Furious form includes agitation, disorientation, seizures, and twitching

Hydrophobia also is seen because of the pain involved with swallowing

  Dumb form - patient is usually paralyzed & disoriented

  Both forms progress to coma and death

  Diagnosis is difficult because symptoms of rabies often mimic other diseases

  Often occurs postmortem

  Requires 6 injections of inactivated vaccine and rabies immune globulin (HRIG) before symptoms




Poliomyelitis (Polio)

  Acute infection of the spinal cord that can cause neuromuscular paralysis

  Caused by Polioviruses and spread via the fecal-oral route

  infects the throat and intestinal tract, invades the bloodstream, and then crosses the blood-brain barrier

  Begins with symptoms of meningitis

  The virus invades and destroys motor neurons of the brain and spinal cord

  leads to paralysis, muscle atrophy, and severe deformities of the trunk and limbs

  Bulbar poliomyelitis - the brain stem, medulla, or cranial nerves are affected

  may require mechanical respirator to breath

  Post-polio syndrome (PPS) - a progressive muscle deterioration that occurs decades later

  Prevented with Salk inactivated, injectable vaccine or Sabin oral attenuated vaccine




  Neuromuscular disease caused by Clostridium tetani

  Bacteria causes an infection at the wound site if anaerobic conditions exist

  puncture wounds, burns, body piercing, tattoos, bites, stings, IV drugs

  Tetanospasmin a neurotoxin that blocks the release of neurotransmitters, resulting in uncontrolled muscle contractions (spastic paralysis)

  Jaw muscles are the first affected = lockjaw

  Death can occur if respiratory muscles are affected

  Immunization with toxoid DTaP booster every 10 years

  anti-toxin is also available (TIG)




  Caused by Clostridium botulinum

  Characterized by dizziness, blurred vision, difficulty swallowing, leading to generalized paralysis and respiratory compromise

  Botulinum toxin - neurotoxin which blocks the release of neurotransmitters and prevents muscle contraction (flaccid paralysis)

  Food-borne Botulism in Children and Adults

  Heat-resistant spores allow the bacteria to survive in improperly processed foods under anaerobic conditions; toxins released in food survive stomach acids

  Infant botulism

  Common in infants who eat contaminated honey   

can develop weak sucking response, generalized loss of tone, and respiratory complications

  Wound botulism

  occurs when spores enter a wound or  puncture, similar to Tetanus

  Botox is weakened form of neurotoxin

  Treat with horse antitoxin




African Sleeping Sickness

  Caused by the protozoan Trypanosoma brucei and transmitted to humans via the bite of a tsetse fly

  maintained in wild and domestic animals and humans

  Initially the organism multiplies in the skin forming a primary chancre, then it enters the lymphatics and blood circulation

  Once the nervous system is involved the patient experiences uncontrollable sleepiness, tremors, shuffling gait, slurred speech, seizures, and local paralysis

  Death results from coma, secondary infections, or heart damage

  Antigenic shift - the protozoan continually changes its surface antigens to evade the hosts IgM response

  Medications are available but have toxic side effects