Question
A twenty five years old man presented with the complaints of frequent passage of profuse, painless, watery diarrhea and copious effortless vomiting for the past two days. He was severely dehydrated and his stool was rice watery with flecks of mucous. Answer the following: What is your diagnosis Name the bacteria causing this disease Mention the mode of transmission of this disease Discuss the laboratory diagnosis of this condition List the preventive measures to be followed to prevent this disease.(1+1+2+4+2)
Answer
Diagnosis: Cholera — profuse, painless, effortless watery diarrhoea and vomiting with severe dehydration and rice-water stool is pathognomonic.
Causative bacteria: Vibrio cholerae (serogroups O1 — biotypes classical and El Tor — and O139).
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 supplies, seafood/shellfish harvested from contaminated water, and poor sanitation are the principal sources, with outbreaks classically associated with floods and disaster situations where water supplies become contaminated.
Laboratory diagnosis
- Direct microscopy — hanging-drop preparation showing characteristic “darting/shooting-star” motility, specifically immobilized by V. cholerae O1/O139 antiserum — rapid presumptive diagnosis.
- String test — a loopful of growth in 0.5% sodium deoxycholate forms a mucoid string when the loop is lifted.
- Culture — enrichment in alkaline peptone water (pH 8.6, selectively favours V. cholerae), then plated on TCBS agar, giving characteristic yellow (sucrose-fermenting) colonies.
- Biochemical confirmation and serotyping — oxidase-positive Gram-negative curved bacilli, confirmed by slide agglutination with specific O1/O139 antisera; O1 further subtyped as Ogawa/Inaba/Hikojima, and biotyped as classical/El Tor.
- Sample transport: stool/rectal swab in Venkatraman-Ramakrishnan (VR) or Cary-Blair medium, avoiding glycerol-based media (toxic to V. cholerae).
Preventive measures 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 (case management, contact tracing, water testing) during epidemics; isolation and appropriate disposal of excreta from cases to prevent secondary spread.