Download Cholera


Cholera is a highly infectious disease.
Infection occurs by the oral route through
contaminated food and drinks. Water born
epidemics are reported. The source of
infection is either a case or a carrier.

The pathogenesis of cholera is dependent on
colonization of the small intestine by the
organism and secretion of enterotoxin.

V. cholera is not an invasive organism, so it
does not reach blood stream (no bacteremia).
 Subcultures
are subsequently made on
alkaline agar or TCBS (Thiosulfate-bile sucrose
medium) medium on which V. cholerae
produces yellow colonies.
The growth is subsequently identified by:
1.
Microscopic examination Fresh examination
demonstrates the actively motile vibrios
under dark field microscopy
2.
Gram-stained smears Show Gram-negative
comma-shaped bacilli, non-spore forming
and non-capsulated
3.
Biochemical reactions and cholera red
reaction
4.
Agglutination with anti-O1 and anti O139
antisera.
Molecular methods:


PCR amplification has been used for the
detection of the cholera toxin A subunit
gene in the rice water stools.
DNA probe for detecting toxigenic V.
cholerae.
Treatment:
 The
most important part is restoration of
fluid and electrolyte balance to correct
dehydration and acidosis by giving
intravenous fluids.
 Antibiotics (tetracyclines) have a secondary
role.
Prevention:
 Public
health measures directed to sewage
disposal, clean water supply, isolation of
cases (similar to s. typhi)
 Chemoprophylaxis
by
tetracyclines
to
exposed persons.
 Vaccines:
 Extract
of killed bacteria given I.M.
 Oral vaccine consisting of inactivated V.
cholerae with B subunits.
 A live attenuating oral vaccine

The efficiency of this vaccine in protection is
disputed as it stimulates antibacterial but not
antitoxic antibodies.

Attempts to develop new vaccines given
orally to protect against cholera toxin are
under trails.
VIBRIO PARAHAEMOLYTICUS
 This
is a marine vibrios requires a high Na cl
concentration to grow (halophilic).
 It
produces blue-green colonies on TCBS
medium.
 It
is associated with food poisoning due to
eating shell fish or raw fish the clinical picture
caused by V. parahaemolyticus varies from
mild to quite severe watery diarrhea.
 The
illness is self limited.
Plesiomonas
 Related to vibrios, but halophilic.
 Plesiomonas shigeloides sometimes causes
water-borne outbreaks of diarrhea in warm
countries.
 (halophilic -requires a high conc. of Nacl to
grow).