UNIT 2

• Cholera is one of the oldest diseases with pandemic potential
• The world has experienced seven cholera pandemics in the last 194 years
• The first cholera pandemic occurred, largely originating in Jessore, India

  1817 - 1923
• The epidemic continued and eventually reached other continents including Europe and the Americas
• Cholera is one of the oldest diseases with pandemic potential
• The world has experienced seven cholera pandemics in the last 194 years
• The first cholera pandemic occurred, largely originating in Jessore, India


  1817 - 1923
• The epidemic continued and eventually reached other continents including Europe and the Americas
• The seventh pandemic began in the Celebes Islands, Indonesia, with spread to Asia, the Middle East, and Africa and continues today

  1961
• In the Philippines, the last case of cholera of the pandemic which commenced March 20, 1902, was reported to have occurred March 8, 1904. During that period 166,252 cases, with 109,461 deaths, were reported
• In 2019, the Department of Health (DOH) reported a 211% increase of reported cholera cases from 918 in 2018 to 2,856 cases in 2019
• Gram-negative curved or comma-shaped bacilli


  • Motile (polar, monotrichous flagellum), EXCEPT Vibrio metschnikovii; they exhibit "darting: or "shooting star" motility
  • Non-spore-forming
  • Facultative anaerobic
  • Aquatic organisms that are found in fresh water, brackish or estuarine water, and marine or salt water
  • Grow in alkaline media
  • Most are halotolerant, some are halophilic
  • Glucose fermentation
  • Catalase(+), EXCEPT Vibrio metschnikovii
  • Oxidase(+), EXCEPT Vibrio metschnikovii
• Kommabacillus


  Common name for V. cholerae because of the characteristic curved or comma-shaped appearance of the individual bacterial cells
• Cholera


  Also known as Asiatic cholera or epidemic cholera
• The incubation period is 12 hours up to 3 days depending on the size of the inoculum ingested
• Symptoms include sudden onset of nausea, vomiting, abdominal cramps and profuse "rice water" diarrhea (stool resembles water in which the rice has been boiled) that may be as many as 10 to 30 per day, containing mucus, epithelial cells, and large numbers of vibrios
• In severe cholera, infected individual can lose several liters of fluid, as much as 20-30 liters per day. If left untreated, it can result in a rapid fluid and electrolyte loss that leads to dehydration, hypovolemic shock, metabolic acidosis, and death in a matter of hours
• Virulence factors of V. cholerae


  • Motility and mucinase
  • Choleragen (cholera toxin)
• How cholera toxin causes disease

  1. The A subunit activates adenylate cyclase, causing increased levels of cyclic adenosine monophosphate (cAMP) and hypersecretion of electrolytes (Na+, K+, HCO3−) and water out of the cell and into the lumen of the intestine

  2. The B subunit binds the A2 subunit to the GM1 ganglioside receptor on the cell membrane of the enterocytes
• H antigen (or flagellar antigen)


  Heat-labile substances that are found in all V. cholerae strains
• O antigen (or somatic antigen)


  Cell wall lipopolysaccharides that confer serologic specificity to the bacterial cells
• Serogroups of V. cholerae


  • V. cholerae O1
  • V. cholerae non-O1
  • V. cholerae O139
• V. cholerae O1


  Is agglutinated by V. cholerae O1 antiserum, includes virulent strains producing cholera toxin, associated with epidemic cholera
• V. cholerae non-O1


  Is NOT agglutinated by V. cholerae O1 antiserum, includes V. cholerae O2 up to V. cholerae O138, does NOT produce cholera toxin but appears to produce an enterotoxin different from cholera toxin, has been associated with isolated cases of diarrheal disease (NOT epidemic-associated)
• V. cholerae O139


  Is NOT agglutinated by V. cholerae O1 antiserum, represented a new serogroup, produces cholera toxin in quantities similar to that produced by V. cholerae O1, has spread in epidemic proportions across the Indian subcontinent
• Biotypes of V. cholerae O1


  • Classical strain
  • El Tor strain
• Classical strain of V. cholerae


  Caused the epidemic cholera from early 1800s to early 1900
• El Tor strain of V. cholerae


  Isolated in the early 1900s from Mecca-bound pilgrims at the El Tor Quarantine Station in Sinai Peninsula, is hardier and better capable of surviving in the environment, associated with the epidemic in the Philippines in 1961 that has started the 7th pandemic, currently the predominant cholera pathogen
• Serotypes of V. cholerae O1

  • Ogawa
  • Inaba
  • Hikojima
• Ogawa and Inaba strains


  Considered the predominant epidemic strains
• Hikojima strain


  Has been isolated in outbreaks, but its occurrence has been rare
• Control rests on education and on improvement of sanitation, particularly of food and water
• Patients should be isolated, their excreta disinfected, and contacts followed up
• Repeated injection of a vaccine containing either lipopolysaccharides extracted from vibrios or dense Vibrio suspensions can confer limited protection to heavily exposed persons (eg, family contacts) but is not effective as an epidemic control measure
• Specimens for laboratory diagnosis


  • Feces (preferred specimen, collected and transported in Cary-Blair medium)
  • Rectal swabs (also acceptable)
• Microscopy


  • Gram-negative curved or comma-shaped bacilli, 2–4 µm long. On prolonged cultivation, vibrios may become straight rods that resemble the Gram-negative enteric bacteria
• Enrichment medium: Alkaline Peptone Water (APW)


  The 1% (w/v) sodium chloride incorporated in this medium promotes the growth of Vibrio species, while the alkalinity (pH 8.6) of this medium inhibits most of the commensal intestinal bacteria
• Alkaline Peptone Water (APW)


  Enrichment medium that promotes the growth of Vibrio species and inhibits most commensal intestinal bacteria
• Enrichment in APW


  1. Done when few organisms are present, as in specimens from convalescent patients and asymptomatic carriers

  2. Not necessary when patient is in very early stages of illness and is passing liquid stool
• 5% Sheep BAM


  • Colonies are typically medium to large, smooth, convex, creamy in consistency, gray-white, and have entire margins, smooth, opaque; may be β-hemolytic