Vibrio cholerae is responsible for causingcholera, whileseveral other species (V. parahaemolyticus, V. vulnificus, V.mimicus, V. alginolyticus) are known to cause shellfish-asso-ciated outbreaks of gastroenteritis.
· Contaminated food and water. Oysters and crabs are noto-rious for harbouring the micro-organism.
· Two types of pathogenic Vibrio cholerae have been identi-fied, both belonging to Group 1:
o The classical biotype which is responsible for the most severe form of the disease (now restricted mainly to Bangladesh).
o The El Tor biotype which is responsible for some of the recent epidemics.
· Both the classical and El Tor vibrios are further divided into 3 serological types—Inaba, Ogawa, and Hikojima. Most of the El Tor vibrios isolated in India belong to the Ogawa serotype.
The main toxin (choleragen, cholera toxin, or CT) is a heat-labile molecule consisting of one A and 5 B sub-units. The former is the active sub-unit, and after being transported into the enterocytes, dissociates into two fragments, A1 and A2. The A1 fragment causes prolonged activation of cellular adenylate cyclate and accumulation of cAMP, leading to outpouring into the small intestinal lumen of large quantities of water and electrolytes, and the consequent watery diarrhoea.
About 1 to 5 days.
1. Cholera usually manifests dramatically and abruptly as profuse painless watery diarrhoea and copious effortless vomiting. Death due to massive loss of fluid and electro- lytes may occur within 24 hours. Stools are colourless and watery with flecks of mucus (rice water stools). There is an inoffensive sweetish odour.
d.Base-deficit acidosis and shock
e. Haemoconcentration and hypokalaemia
a.Stool specimen is best collected by introducing a lubri- cated rubber catheter into the rectum and letting the liquid stool flow directly into a screw-capped container. Alternatively, rectal swabs can be used.
b.Stools must be transported at 4°C or in some appro- priate holding medium such as VR (Venkatraman- Ramakrishnan) medium or alkaline peptone water. If transport media are not available, strips of blotting paper may be soaked in the watery stool and sent to the laboratory packed in plastic envelopes.
c.Diagnosis may be accomplished by demonstration of motile vibrio under dark field or phase contrast micros- copy, and by culture in appropriate media.
2. Analysis of suspect water sample: By culture.
3. Serological examination: This is generally not helpful in diagnosis, but may help in assessing the prevalence of cholera in a region.
o Rapid fluid and electrolyte replacement.
o Antibiotic therapy: Tetracycline and doxycycline are the antibiotics of choice. Many strains are resistant to cotri- moxazole and furazolidone.
o Antiemetics, antidiarrhoeals, and antispasmodics are contraindicated.
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