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General Microbiology II

Central Nervous System Infections

• Botulism
  • epidemiology: botulism is caused by ingestion of botulin produced by Clostridium botulinum in foods contaminated with spores and improperly canned (~20 cases per year in US); Did ya know ... infant botulism is an infectious disease transmitted by infants eating honey, which may contain Clostridium botulinum spores?
  • pathogenesis: after 12-36 hour incubation period, exotoxin (botulin) causes flaccid paralysis of neck and chest, which can cause death (up to 70% of untreated cases; ~5% of treated cases) due to cardiac and/or respiratory failure
  • treatment: antitoxin (available from CDC)
  • prevention: avoid ingestion of contaminated foods via better food washing and canning techniques (sanitation)
• Tetanus
  • epidemiology: Clostridium tetani; endospores of this bacterium enter body via animal bites, scratches, puncture wounds; fewer than 10 cases per year in US ... more info ... more info
  • pathogenesis: toxin (tetanospasmin) causes CNS damage (4-21 days); complications - respiratory failure causes death (70% of patients die)
  • treatment: antitoxin; penicillin; valium, barbituates (minimize damage)
  • prevention: antitoxin, vaccine (DPT vaccine @ 2, 4, 6, 18 months and Td vaccine boosters at 7-10 year intervals)
• Encephalitis
  • epidemiology: Encephalitis viruses are transmitted by mosquitoes (Culex tarsalis; others); reservoirs are other animals, including birds, reptiles and horses; infection is most prevalent in summer and fall; found in many places in the world, these diseases cause 150-3,000 cases per year in the US despite our expenditure of ~$150 million per year dealing with viruses encephalitis transmitted by mosquitos (including estimated cost of vector control and surveillance activities); ~800 primary cases of non-West Nile encephalitis per year in the US (~150 post-infection cases); the newest member of this group in the US is West Nile Fever is a recently emerging encephalitic disease in the US that sickened 4156, and killed 284, people during 2002 ... distribution info
  • pathogenesis: mosquito "injects" virus into bloodstream; virus replicates in the CNS, causing fever and headache, vomitting,stiff back and neck, drowsiness, tremors, loss of coordination, convulsions, seizures; complications - may lead to coma as a result of CNS damage (can lead to mental impairment (retardation in children), paralysis) and death occurs in 1-60%, depending upon the virus responsible; in West Nile encephalitis, the death rate is ~7% and the leading cause of death in 25% of victims is weakness in the muscles involved in breathing (most victims are over 65 years of age)
  • treatment: TLC ... management of symptoms and complications
  • prevention: vaccines (none for West Nile Fever); mosquito repellent use; mosquito control
• Poliomyelitis
  • epidemiology: Polio Virus (virus) is transmitted via water (summer); fewer than 10 cases per year in the US; ~270,000 cases (~25,000 deaths) per year, worldwide; polio costs ~$1.5 billion per year ($230 million in the US)
  • pathogenesis: intestinal infection leads to infection of motor neurons, damage causes paralysis; complications include muscle atrophy, paralysis, death (postpolio syndrome, which only affects those who had polio earlier in their lives, and for which there is some help)
  • treatment: TLC, supportive measures ... such as braces, wheelchairs or iron lungs
  • prevention:
    • sanitation ... adequate treatment of drinking water and prevention of its contamination with sewage
    • vaccines
      • injectable polio vaccine (IPV)
        • inactivated viruses - doesn't cause disease, but induces production of neutralizing antibodies (only)
        • Jonas Salk developed this vaccine
      • oral polio vaccine (OPV)
        • attenuated, infectious viruses - can cause disease in immunocompromised children, but induces CTLs as well as neutralizing antibodies
        • Albert Sabin developed this vaccine
      • CDC recently decreed that only IPV should be used for vaccinating infants in the US
      • World Health Organization (WHO) is spearheading a move to eradicate polio, and good progress is being made in this effort
• Mad Cow Disease (Bovine Spongiform Encephalopathy)
  • epidemiology: Prusiner established that prions are ingested by people eating beef from cattle stricken with Bovine Spongioform Encephalopathy (BSE); this disease was discovered in Great Britain in the 1980s, and ~200 people have died of it so far, but BSE has yet to emerge in the US
  • pathogenesis: prions are taken up from the digestive tract and somehow get into the brain, where they interact with cell receptors, changing their shape or conformation, which causes accumulation of prion molecules as the cells replace the altered receptor molecules; this causes accumulation of fibrils of insoluble prion complexes and results in slow degeneration of the central nervous system with obvious dysfunction, progressive dementia, and vacuolar degeneration of the brain known as new variant Creutzfeldt-Jakob disease (nvCJD)
  • treatment: TLC
  • prevention: avoid eating beef that may contain prions ... how to tell if your cow has mad cow disease ... mad cow meets bird flu