Question
Four workers from a construction site were admitted in a primary health centre with watery diarrhoea, fatigue and muscle cramps. On examination, they were dehydrated with tachycardia. The stool samples were collected for examination and appeared like rice water. The bacteria isolated in stool culture was comma shaped and motile.
- (a) What is the most probable clinical diagnosis
- (b) Name the causative agent.
- (c) Write the mode of transmission of the infective agent
- (d) Describe the pathogenesis of the condition e) Write briefly on the laboratory diagnosis f) How will you treat the condition g) Write briefly on the prophylaxis (1+1+1+3+3+3+3) (P.T.O)
Answer
a) Most probable clinical diagnosis: Cholera — watery diarrhoea, dehydration, tachycardia, rice-water stool, with a comma-shaped, motile bacterium isolated in culture is classical.
b) Causative agent: Vibrio cholerae (serogroups O1 — biotypes classical and El Tor — and O139).
c) Mode of transmission: faecal-oral route — ingestion of water or food contaminated with the organism from the faeces of an infected patient or asymptomatic carrier; contaminated drinking water, poor sanitation, and shellfish/seafood from contaminated water are common sources, with this construction-site outbreak scenario suggesting a shared contaminated water/food source among the workers.
d) Pathogenesis V. cholerae is non-invasive; it colonizes the small intestinal mucosa via flagellar motility and adhesins, without penetrating the epithelium. The organism elaborates cholera toxin, an AB-type exotoxin — the B subunit binds the GM1 ganglioside receptor on enterocytes, facilitating entry of the A subunit, which ADP-ribosylates the Gs protein, causing persistent activation of adenylate cyclase and a sustained rise in intracellular cAMP. This drives massive, unregulated active secretion of chloride (and passive water/sodium/bicarbonate) into the gut lumen, overwhelming the intestine’s absorptive capacity and producing the profuse, isotonic, rice-water diarrhoea, rapidly leading to severe dehydration, hypovolaemic shock, and muscle cramps (from electrolyte loss) if untreated.
e) Laboratory diagnosis
- Direct microscopy — hanging-drop preparation showing characteristic “darting/shooting-star” motility, immobilized by specific antiserum.
- String test — a rapid presumptive test (mucoid string formation in 0.5% sodium deoxycholate).
- Culture — enrichment in alkaline peptone water (pH 8.6), then plated on TCBS agar, giving characteristic yellow (sucrose-fermenting) colonies.
- Biochemical confirmation and serotyping — slide agglutination with specific O1/O139 antisera; O1 further subtyped as Ogawa/Inaba/Hikojima.
f) Treatment Rehydration is the cornerstone — Oral Rehydration Solution (ORS) for mild-moderate dehydration; intravenous fluids (e.g., Ringer’s lactate) for severe dehydration/shock; antibiotics (doxycycline, azithromycin, or ciprofloxacin) shorten the duration of illness and reduce stool volume/vibrio shedding, though rehydration remains the priority and life-saving intervention.
g) Prophylaxis Safe drinking water supply and proper sanitation/sewage disposal; food hygiene and thorough cooking of seafood; hand hygiene and health education; oral cholera vaccines (killed whole-cell, e.g., Dukoral, Shanchol) for high-risk populations/outbreak settings; chlorination of water sources and prompt outbreak response during epidemics.