Questions and Answers
What is the primary causal agent of cholera?
Vibrio cholerae
Which biotype of Vibrio cholerae is currently the predominant cholera pathogen worldwide?
Cholera can be transmitted through the fecal-oral route.
True
What are the two main reservoirs for Vibrio cholerae?
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Cholera has ______ main biotypes.
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What is the incubation period for cholera?
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Which symptom is typically absent in cholera patients?
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What is the preferred solution for rehydration in cholera treatment?
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Which of the following complications can arise from untreated cholera?
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Antibiotic therapy for cholera should be started only after laboratory confirmation.
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What type of Shigella causes the most severe epidemics?
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What is the typical symptom of Shigella infection?
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Study Notes
Epidemiology of Cholera
- Cholera is caused by the bacterium Vibrio cholerae, discovered in 1883 by Robert Koch.
- There are two major biotypes: classical and El Tor, with El Tor being the predominant pathogen worldwide.
- The bacterium is a comma-shaped, gram-negative, aerobic bacillus measuring 1-3 mm in length and 0.5-0.8 mm in diameter.
History of Cholera Pandemics
- There have been seven cholera pandemics since 1817, with the seventh pandemic starting in Indonesia in 1961 and affecting more countries and continents than the previous six.
- The first six pandemics were caused by V. cholerae classical biotype, while the seventh pandemic was caused by V. cholerae El Tor biotype.
Epidemiology of Cholera
- Cholera is transmitted through contaminated water and food, with person-to-person infection being rare.
- The infectious dose of bacteria required to cause clinical disease varies with the source, with 10^3-10^6 organisms needed when ingested with water and 10^2-10^4 when ingested with food.
- Crowding and gathering of people during religious rituals can enhance the spread of infection.
- Index cases who travel back to their homes can pass the organism to at-risk individuals, leading to secondary epidemics or small-scale infections.
Pathogenesis
- V. cholerae causes clinical disease by producing an enterotoxin that promotes the secretion of fluid and electrolytes into the lumen of the gut.
- The enterotoxin acts locally and does not invade the intestinal wall, resulting in few WBC and no RBC found in the stool.
- Fluid loss originates in the duodenum and upper jejunum, with the colon being in a state of absorption, resulting in severe diarrhea.
Clinical Picture
- The incubation period is 24-48 hours, with symptoms beginning with sudden onset of watery diarrhea, which may be followed by vomiting.
- Fever is typically absent, and the diarrhea has a fishy odor in the beginning but becomes less smelly and more watery over time.
- In severe cases, stool volume exceeds 250 ml/kg, leading to severe dehydration, shock, and death if untreated.
At-Risk Groups
- All ages are affected, but children and the elderly are more severely affected.
- Subjects with blood group "O" are more susceptible, and those with reduced gastric acid production are at increased risk.
Diagnosis
- The organism can be seen in stool by direct microscopy after gram stain and dark field illumination to demonstrate motility.
- Cholera can be cultured on special alkaline media like triple sugar agar or TCBS agar.
- Serologic tests are available to define strains, but this is needed only during epidemics to trace the source of infection.
Treatment
- The primary goal of therapy is to replenish fluid losses caused by diarrhea and vomiting.
- Fluid therapy is accomplished in two phases: rehydration and maintenance.
- Ringer lactate solution is preferred over normal saline because it corrects the associated metabolic acidosis.
- IV fluids should be restricted to patients who purge >10 ml/kg/h and for those with severe dehydration.
Cholera Vaccines
- Two new oral vaccines became available in 1997: a killed and a live attenuated type.
- Both vaccines provoke a local immune response in the gut and a blood immune response.
- Cholera vaccination is no longer required for international travelers because the risk is small.
Shigellosis
- Shigellosis is a bacterial dysentery caused by four species of Shigella: boydii, dysenteriae, flexneri, and sonnei.
- Shigella dysenteriae causes deadly epidemics, while flexneri and sonnei are more common in the US, with 448,240 cases reported last year.
Signs and Symptoms
- Shigellosis causes diarrhea (bloody), fever, and stomach cramps, usually resolving in 5-7 days.
- Children and the elderly may have diarrhea so severe that they need to be hospitalized.
- Severe infection in a child less than 2 may cause seizures, and some show no signs at all but still pass the Shigella bacteria to others.
Diagnosis
- Determining that Shigella is the cause of the illness depends on laboratory tests.
- Tests identify if it is Shigella and what type, and stools of an infected person are tested.
- Diarrhea with blood and mucus is a typical symptom of Shigella.
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Description
This quiz covers the background and epidemiology of Cholera, a disease caused by Vibrio cholerae bacteria. It was first discovered by Robert Koch in 1883 and has two major biotypes: classical and El Tor.
