Chapter 19

 

Infectious Diseases Affecting the Nervous System

 

 

Meningitis

   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

   Meningococcal Meningitis

  can result in shock and death within 24 hours after infection

  associated with epidemics; most cases are in children younger than 2

  The causative agent is Neisseria meningitidis

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

  N. meningitis in the nervous system causes a massive inflammatory response, causing brain swelling and infarcts

  bacteria and leukocytes degrade glucose in cerebrospinal fluid potentially depriving the brain of nutrients

  N. meningitis produces an endotoxin that causes a drop in blood pressure leading to shock

  Polysaccharide conjugate vaccine available or antibiotic prophylaxis

 

   Streptococcus pneumoniae

  gram positive coccus that is alpha-hemolytic

  leading cause of community-acquired meningitis

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

  polysaccharide conjugate vaccine available or antibiotics

  Prevnar for children; Pneumovax for adults

 

   Haemophilus influenza

  gram negative pleomorphic rods

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

  conjugate polysaccharide vaccine available or antibiotic prophylaxis

 

   Listeriosis

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

  The causative agent is Listeria monocytogenes

  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

 

   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

  Person to person transmission does not occur

  Treat with anti-fungals for several weeks

 

   Coccidioides immitis

  Coccioidomycosis - a 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

  Usually transmitted from mother to baby in utero or during birth

  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

          

 

 

Meningoencephalitis

   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

   Toxoplasmosis

  Caused by the protozoan Toxoplasma gondii

  Can infect many species but cats are the  primary host

  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

 

 

Rabies

   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

   The disease progresses through identifiable stages

   Incubation lasts 1-2 months

  Occurs at the wound site

  Some feel pain, burning, & tingling

   Prodromium

  Characterized by fever, anorexia, nausea, vomiting, headache, sore throat, muscle aches, and fatigue

   Acute neurological phase

  Furious form

  Agitation, disorientation, seizures, confusion, light sensitivity, hallucination, and twitching

  Hydrophobia also is seen because of the pain involved with swallowing

  Dumb form

  Patient is usually paralyzed, & disoriented

   Coma

   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 in 25-50% of patients

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

 

 

Tetanus

   Caused by Clostridium tetani

  a gram-positive, spore-forming rod found in the soil and the GI tract of animals

   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 DPT booster every 10 years

  anti-toxin is also available (TIG)

 

 

Botulism

   Caused by Clostridium botulinum

  An anaerobic, gram-positive spore-forming rod  found in the soil and GI tract of animals

   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

  Most common type in US

  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