Cholera (Vibrio cholera)

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Cholera (Vibrio cholera)
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Introduction

• Cholera, sometimes known as Asiatic cholera or
  epidemic cholera, is an infectious
  gastroenteritis caused by the bacterium Vibrio
  cholerae.12
• Transmission to humans occurs through ingesting
  contaminated water or food.
• The major reservoir for cholera was long assumed
  to be humans themselves, but considerable
  evidence exists that aquatic environments can
  serve as reservoirs of the bacteria.

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• Vibrio cholerae is a Gram-negative bacterium that
  produces cholera toxin, an enterotoxin, whose
  action on the mucosal epithelium lining of the
  small intestine is responsible for the
  characteristic massive diarrhoea of the
  disease.1
• In its most severe forms, cholera is one of the
  most rapidly fatal illnesses known, and a healthy
  person may become hypotensive within an hour of
  the onset of symptoms infected patients may die
  within three hours if treatment is not
  provided.1

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• In a common scenario, the disease progresses from
  the first liquid stool to shock in 4 to 12 hours,
  with death following in 18 hours to several days
  without oral rehydration therapy.

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Symptoms

• The diarrhea associated with cholera is acute and
  so severe that, unless oral rehydration therapy
  is started promptly, the diarrhea may within
  hours result in severe dehydration (a medical
  emergency), or even death.
• Author Susan Sontag wrote that cholera was more
  feared than some other deadly diseases because it
  dehumanized the victim. Diarrhea and dehydration
  were so severe the victim could literally shrink
  into a wizened caricature of his or her former
  self before death.5
• Other symptoms include rapid dehydration, rapid
  pulse, dry skin, tiredness, abdominal cramps,
  nausea, and vomiting.
• Traditionally, Cholera was widespread throughout
  third world countries, however more recently
  outbreaks have occurred in more rural parts of
  England and the United States' mid-west region.

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Treatment

• Water and electrolyte replacement are essential
  treatments for cholera, as dehydration and
  electrolyte depletion occur rapidly.
• Prompt use of oral rehydration therapy is highly
  effective, safe, uncomplicated, and inexpensive.
• The use of intravenous rehydration may be
  absolutely necessary in severe cases, under some
  conditions.
• In addition, tetracycline is typically used as
  the primary antibiotic, although some strains of
  V. cholerae exist that have shown resistance.

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• Other antibiotics that have been proven effective
  against V. cholerae include cotrimoxazole,
  erythromycin, doxycycline, chloramphenicol, and
  furazolidone.6 Fluoroquinolones such as
  norfloxacin also may be used, but resistance has
  been reported.7
• Recently Hemendra Yadav reported his findings at
  A.I.I.M.S., New Delhi that Ampicillin resistance
  has again decreased in V.cholerae strains of
  Delhi.
• Rapid diagnostic assay methods are available for
  the identification of multidrug resistant V.
  cholerae.8 New generation antimicrobials have
  been discovered which are effective against V.
  cholerae in in vitro studies.

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Holding or transport media

• Venkataraman-ramakrishnan (VR) medium This
  medium has 20g Sea Salt Powder and 5g Peptone
  dissolved in 1L of distilled water.
• Cary-Blair medium This the most widely-used
  carrying media. This is a buffered solution of
  sodium chloride, sodium thioglycollate, disodium
  phosphate and calcium chloride at pH 8.4.
• Autoclaved sea water

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Enrichment media

• Alkaline peptone water at pH 8.6
• Monsur's taurocholate tellurite peptone water at
  pH 9.2

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Vaccine for cholera

• A recently developed oral vaccine for cholera is
  licensed and available in other countries
  (Dukoral from SBL Vaccines).
• The vaccine appears to provide somewhat better
  immunity and have fewer adverse effects than the
  previously available vaccine.
• However, CDC does not recommend cholera vaccines
  for most travelers, nor is the vaccine available
  in the United States . Further information about
  Dukoral can be obtained from the manufacturers
• Dukoral SBL Vaccin AB, SE-105 21 Stockholm,
  Swedentelephone 46-8-7351000,e-mail
  info_at_sblvaccines.sewebsite www.sblvaccines.se

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• Pathogenesis and Epidemiology of cholera
• Virulence factor
• Colonization of the small Intestinal Mucosa
• Cholera toxin
• Other toxin produced by V. cholerae
• Virulence gene Cassette ctx, ace and zot
• Transcriptional Regulation of Virulence Genes
• toxR, ToxS, ToxT System

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Plating media

• Alkaline bile salt agar (BSA) The colonies are
  very similar to those on nutrient agar.
• Monsur's gelatin Tauro cholate trypticase
  tellurite agar (GTTA) medium Cholera vibrios
  produce small translucent colonies with a greyish
  black centre.
• TCBS medium This the mostly widely used medium.
  This medium contains thiosulphate, citrate, bile
  salts and sucrose. Cholera vibrios produce flat
  2-3 mm in diameter, yellow nucleated colonies.
• Direct microscopy of stool is not recommended as
  it is unreliable. Microscopy is preferred only
  after enrichment, as this process reveals the
  characteristic motility of Vibrios and its
  inhibition by appropriate antiserum. Diagnosis
  can be confirmed as well as serotyping done by
  agglutination with specific sera.

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Biochemistry of the V. cholerae bacterium

• Most of the V. cholerae bacteria in the
  contaminated water that a host drinks do not
  survive the very acidic conditions of the human
  stomach.
• The few bacteria that do survive conserve their
  energy and stored nutrients during the passage
  through the stomach by shutting down much protein
  production.
• When the surviving bacteria exit the stomach and
  reach the small intestine, they need to propel
  themselves through the thick mucus that lines the
  small intestine to get to the intestinal wall
  where they can thrive.
• V. cholerae bacteria start up production of the
  hollow cylindrical protein flagellin to make
  flagella, the curly whip-like tails that they
  rotate to propel themselves through the mucous
  that lines the small intestine.

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• Once the cholera bacteria reach the intestinal
  wall, they do not need the flagella propellers to
  move themselves any longer.
• The bacteria stop producing the protein
  flagellin, thus again conserving energy and
  nutrients by changing the mix of proteins that
  they manufacture in response to the changed
  chemical surroundings.
• On reaching the intestinal wall, V. cholerae
  start producing the toxic proteins that give the
  infected person a watery diarrhoea.
• This carries the multiplying new generations of
  V. cholerae bacteria out into the drinking water
  of the next hostif proper sanitation measures
  are not in place

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• On reaching the intestinal wall, V. cholerae
  start producing the toxic proteins that give the
  infected person a watery diarrhoea.
• This carries the multiplying new generations of
  V. cholerae bacteria out into the drinking water
  of the next hostif proper sanitation measures
  are not in place

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• Microbiologists have studied the genetic
  mechanisms by which the V. cholerae bacteria turn
  off the production of some proteins and turn on
  the production of other proteins as they respond
  to the series of chemical environments they
  encounter, passing through the stomach, through
  the mucous layer of the small intestine, and on
  to the intestinal wall.
• Of particular interest have been the genetic
  mechanisms by which cholera bacteria turn on the
  protein production of the toxins that interact
  with host cell mechanisms to pump chloride ions
  into the small intestine, creating an ionic
  pressure which prevents sodium ions from entering
  the cell.

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• The chloride and sodium ions create a salt water
  environment in the small intestines which through
  osmosis can pull up to six liters of water per
  day through the intestinal cells creating the
  massive amounts of diarrhoea.
• The host can become rapidly dehydrated if an
  appropriate mixture of dilute salt water and
  sugar is not taken to replace the blood's water
  and salts lost in the diarrhoea

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