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:
The classical biotype which is
responsible for the most severe form of the disease (now restricted mainly to
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
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.
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.
acidosis and shock
Haemoconcentration and hypokalaemia
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.
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.
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.
Rapid fluid and electrolyte
Antibiotic therapy: Tetracycline and
doxycycline are the antibiotics of choice. Many strains are resistant to cotri-
moxazole and furazolidone.
Antiemetics, antidiarrhoeals, and
antispasmodics are contraindicated.