17.3

• Meningitis


  Inflammation of the meninges - can have many causes, including the ingestion of poisons, the ingestion or injection of drugs, a reaction to a vaccine, or a pathogen
• Causes of meningitis


  • Virus
  • Bacterium
  • Fungus
  • Protozoan
• Viral meningitis


  May be caused by a virus that specifically infects the meninges, or may be the result of an immune reaction to a virus that does not specifically infect the brain
• Viral meningitis is sometimes referred to as "aseptic meningitis" because in about 50% of the cases the pathogen cannot be identified
• Viruses that cause meningitis

  • Enteroviruses
  • Coxsackieviruses
  • Echoviruses
  • Mumps virus
  • Arboviruses
  • Poliovirus
  • Adenoviruses
  • Measles virus
  • Herpes simplex
  • Varicella virus
• Viral meningitis tends to be less serious than bacterial meningitis
• Historical major causes of bacterial meningitis

  • H. influenzae
  • N. meningitidis
  • S. pneumoniae
• All three of these bacterial pathogens now have vaccines that have dramatically reduced the incidence of meningitis in the United States
• In third world countries, meningitis caused by these organisms is still commonplace
• Less common causes of bacterial meningitis

  • Listeria monocytogenes
  • S. aureus
  • Pseudomonas aeruginosa
  • Salmonella spp.
  • Klebsiella spp.
• Major causes of bacterial meningitis in neonates

  • Streptococcus agalactiae (Group B, β-hemolytic streptococci)
  • E. coli and other members of the family Enterobacteriaceae
  • L. monocytogenes
• Symptoms of bacterial meningitis

  • Fever
  • Headache
  • Stiff neck
  • Sore throat
  • Vomiting
  • Dizziness
  • Convulsions
  • Minor paralysis
  • Coma
• Meningitis is a medical emergency, and steps must be taken immediately to determine the cause
• Diagnosis is usually made by a combination of patient symptoms, physical examination, and Gram staining and culture of the CSF
• Parasites that can cause CNS diseases

  • Free-living amebas (Naegleria, Balamuthia, Acanthamoeba)
  • Toxoplasma
  • Trypanosoma
• Occasionally, fungal pathogens, especially Cryptococcus neoformans (an encapsulated yeast), cause meningitis
• Examples of bacterial neurotoxins

  • Botulinum toxin
  • Tetanospasmin
• Diseases caused by fungal toxins (mycotoxins)

  • Ergot from grain moulds
  • Mushroom poisoning
• Gymnodinium, an alga found in algal "blooms", produces neurotoxins, which may concentrate in bivalve shellfish and cause paralytic symptoms following ingestion of the contaminated shellfish
• A variety of other algae also produce neurotoxins
• Opportunistic infections (OIs)


  Infections that normally would not occur in healthy, immunocompetent individuals or would, at most, cause only mild infections, but are relatively common in immunosuppressed individuals and often contribute to their death
• Examples of common opportunistic infections

  • Aspergillosis and other mould infections
  • Candidiasis
  • Cytomegalovirus infection
  • Herpes simplex virus infections
  • Malaria
  • Mycobacterium avium complex
  • Pneumocystis pneumonia
  • Toxoplasmosis
  • Tuberculosis
• In the late 1960s, the Surgeon General of the United States declared that it was time to close the book on infectious diseases and, to instead, pay closer attention to chronic ailments, such as cancer and heart disease
• Examples of emerging infectious diseases in the past 30 years

  • Avian influenza ("bird flu")
  • Chikungunya virus infection
  • Cryptococcus gattii infection
  • Cryptosporidiosis
  • Dengue fever and dengue hemorrhagic fever
  • E. coli O157 infections
  • Ebola hemorrhagic fever
  • Hantavirus pulmonary syndrome
  • Hendra virus infection
  • HIV infection and AIDS
  • Human monkeypox
  • Lassa fever
  • Legionellosis
  • Lyme disease
  • Marburg hemorrhagic fever
  • Middle East respiratory syndrome (MERS)
  • Nipah virus encephalitis
  • Severe acute respiratory syndrome (SARS)
  • Variant Creutzfeldt-Jakob disease
  • West Nile virus encephalitis
  • Zika virus infection
• Causes of reemerging infectious diseases

  • Pathogen mutations and genetic recombinations
  • Acquired drug resistance
  • Decreased compliance with vaccination policies and other breakdowns in public health measures
  • Population shifts
  • War and civil conflicts
  • Famine
  • Floods
  • Droughts
  • Bioterrorism
• Examples of infectious diseases that have reemerged or shown up in new geographic areas in recent years


  • Chikungunya
  • Cholera
  • Dengue fever
  • Diphtheria
  • Malaria
  • Rift Valley fever
  • Tuberculosis
  • West Nile encephalitis
  • Yellow fever
  • Zika virus
  • Infections caused by methicillin-resistant S. aureus and other "superbugs"
• The microbiome has been under attack ever since the dawn of the antibiotic era, and recent studies have linked changes in the microbiome to some of the most pressing medical problems of our time, including obesity, allergies, diabetes, bowel disorders, and even psychiatric problems like autism, schizophrenia, and depression