Human Diseases Worldwide

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Human Diseases Worldwide

• Diarrheal diseases account for 16 of human
  illness
• 2-4 billion cases/yr 3-5 million deaths/yr
  (mostly children lt5 yrs)
• 50 of diarrheal disease caused by bacteria
• most severe diarrheal disease is cholera
• most common diarrheal disease caused by
  enterotoxigenic E. coli
• one billion cases/yr 300,000-500,000 deaths/yr
  (young children)

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Vibrio cholerae and Enterotoxingenic E. coli
(ETEC)

• Organism similarities
• Gram negative organisms
• Adhere to small intestine (uppermost 20 of gut)
• Gastrointestinal pathogens contracted by
  consumption of contaminated water (fecal oral
  route)
• Cause diarrheal disease
• Similar virulence strategy and factors
• Neither organism induces histological changes in
  gut epithelium

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V. Cholerae and ETEC Disease

• V. cholerae causative agent of cholera
• severe diarrhea only observed in humans
• massive fluid loss (up to 20L/day)
• 30 mortality without supportive therapy (rapid
  dehydration resulting in hypovolemic shock)
• epidemic disease (7 pandemics)
• first reported in India, 1817
• current pandemic began 40 years ago in
  Bangladesh
• endemic in areas with poor sanitation
• ETEC causes cholera-like disease
• causes disease in humans, calves and piglets
• diarrheal disease less severe than cholera
• not associated with epidemics
• primarily observed in impoverished children
• number one cause of bacterial diarrheal disease
  worldwide

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Cholera and the Birth of Epidemiology

• Grim urban conditions fueled cholera spread
• industrial revolution attracted and concentrated
  people in cities
• cities lacked infrastructure to support ever
  growing masses
• Pestilential odors rose from over 200K cesspools
  and accumulated sewage piled up in every ditch
  and alleyway sewage overflowed from storm-water
  sewers during rainstorms and Thames's high tides
• Rivers viewed as a waste-disposal system Thames
  became a reeking brown sewer scenario pervasive
  across Europe
• 1858, London wrapped in "The Great Stink" due to
  Thames contamination
• Cholera outbreak kills hundreds of thousands
• Germ theory of disease not established
• disease caused by supernatural forces or miasma
  (bad air)
• public health efforts focused on locating bad
  air source
• pleasant or strong smelling odors protective
• herbs, alcohol, smoke

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Cholera and the Birth of Epidemiology (cont.)

• John Snow, English anesthesiologist
• Argued that cholera transmitted by contaminated
  food or water
• couldn't be airborne because it didn't affect
  the lungs
• theory was ignored because he couldn't identify
  the "poison" in the water
• Mapped cholera outbreaks in London to discern
  how the disease spread

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Cholera and the Birth of Epidemiology (cont.)

• Mapped outbreaks to a water pump on Broad Street
• most infected people had drank water from pump
• those who did not live in area came to this pump
  for water because it tasted better than other
  city water
• Snow recommended that the Broad Street pump
  decommission
• pump handle removed
• number of new cholera cases decreased
  dramatically
• Medical community not convinced cholera was
  spread by contaminated water

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Cholera and the Birth of Epidemiology (cont.)

• Two London water companies supplied one area of
  city
• both provided water directly from the Thames
• Southwark and Vauxhall company water from within
  city limits
• Lambeth company water acquired upstream of
  London
• Snow documented number of deaths/water company
• Southwark and Vauxhall water 70/10,000 deaths
• Lambeth company water 5/10,000 deaths
• Findings sparked massive public concern
• sanitary reform followed
• Final London cholera epidemic in 1866
• 2200 deaths

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Cholera Remains a Serious Threat

• Inadequate sanitation and access to clean water
  fuel endemic and pandemic disease

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Vibrio cholerae Virulence Factors

• Evolution
• V. cholerae are non-pathogenic marine organisms
  present in all oceans
• Virulence consequence of infection of 2
  serotypes (O1 and O139) with bacteriophages that
  encode elements essential for disease
• Adhesions
• Toxin co-regulated pilus (Tcp)
• hair-like appendages extend from bacteria,
  contact host cell
• Encoded within the Vibrio pathogenicity island
  (VPI) maybe phage genome
• Essential for adhesion to upper 20 of intestine
• Only known to cause disease in humans
• Toxin
• Encoded on a filamentous bacteriophage genome
  (separate from VPI)
• Disrupts electrolyte balance resulting in fluid
  secretion
• Infects V. cholerae through TCP
• Virulence factor regulation
• Tightly regulated expression governed by sensors
  of 2 environmental cues
• Cell density dependent signal (Quorum sensing)

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ETEC Virulence Factors

• Evolution
• ETEC likely derived from gt70 different commensal
  E. coli strains
• Virulence consequence of acquisition of
  plasmid(s)
• Adhesions
• Plasmid encoded
• Attachment fimbriae termed colonization factor
  antigens (CFA)
• gt20 different CFA variants identified
• Adhesions likely associated with host
  specificity (humans, calves, piglets)
• Toxins (strains may express 1 or more toxins)
• Heat-labile toxin (LT)
• Plasmid encoded
• Identical to Cholera toxin (CT)
• ETEC strains do not secrete LT/CT as efficiently
  as V. cholerae
• V. cholerae CT secretion mediated by dedicated
  T2SS
• ETEC genome does not encode dedicated T2SS
• diminished toxin secretion (10) maybe
  associated with less severe disease
• Heat-stabile toxins A and B (STa and STb)

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ETEC Heat Stabile (ST) Toxins

• STa toxins
• encoded within a composite transposon located on
  plasmids
• small peptides (11-18 amino acids)
• associated with porcine, bovine, and human ETEC
  strains
• stimulates guanylate cyclase system
• cGMP accumulation diminished water and
  electrolyte absorption
• STb toxins
• encoded within a composite transposon
• small peptide (48 amino acids)
• associated with porcine ETEC strains
• does not increase cyclic nucleotide accumulation
  (mechanism not established)

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Cholera Toxin

• CTX phage lysogenic filamentous virus buds from
  cell (no lysis)
• CT produced in gut lumen following attachment to
  enterocytes
• Pentomeric CT subunit B (CTB) binds toxin to
  host cell GM1 ganglioside receptors on enterocyte
  apical membrane surface CT internalized into
  cell inside membrane bound vesicle
• CT escapes into host cell cytosol
• CT subunit A (CTA)
• synthesized as single protein
• cleaved into 2 subunits (CTA1 and CTA2) by V.
  cholerae protease A subunits are joined via
  disulfide bond
• CTA1 subunit is an ADP ribosylating enzyme
  (toxic activity)
• CTA2 mediates insertion into CTB pentamer
• CTA2 subunit KDEL C-terminus mediates CTA escape
  into cytosol

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Cholera Toxin A 1 Enzyme Activity

• ADP ribosylates the heterotrimeric Gsalpha
  subunit of Adenylate Cyclase

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• ON ADP-ribosyl adenylate cyclase increases
  cellular cAMP
• cAMP activates PKA and PO4 (activation) of major
  intestinal chloride channel (CFTR)
• CFTR activation increases Cl- secretion
• change in osmotic balance leads to fluid
  secretion

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Vibrio cholerae Ecology

• V. cholerae are marine organisms present in all
  oceans
• Organism is sensitive to stomach acid
• Relatively high infectious dose
• Inconsistent with ability to cause epidemics
• Oceanic V. cholerae present in viable
  non-culturable state
• Organisms shed in cholera rice water stools are
  more infective than those cultured in lab
• Microscopic analyses demonstrated stool and
  oceanic viable non-culturable V. cholerae present
  in biofilms

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Vibrio cholerae Bioflims

• V. cholerae biofilms bind marine organisms
  (copepods) and phytoplankton
• Biofilm V. cholerae in quiescent state
• resistant to environmental stresses including
  acid

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Infectivity of V. cholerae Bioflims

• Observations influencing anti-cholera practices
  and policies

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Ocean Climate Influences V. cholerae Outbreaks
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New Methods to Monitor Oceanic V. cholerae

• Satillite surveillance of ocean temperatures
• Monitoring of copepod and phytoplankton blooms
• Monitoring of oceanic phages that kill V.
  cholerae