16. PATHOGENESIS
- V. cholera 01 causes an acute
diarrhoeal disease known as
cholera.
- It occurs only in man. The faeces
and vomitus of human cases or
carriers are the main source of
infection.
22. Contd...
- After passing the acid barrier of the
stomach, virulent vibrio cholera adhere
to the microvilli (brush border) of small
intestine mucosa and multiply and
secrete cholera toxin.
- The cholera toxin (CT) consist of two
major non covalently associated regions
: ‘ A’ active region (sub unit) and ‘B’
binding sub unit.
23. Contd...
- V. cholera 01 protease yield 2 fragments A1 and A2
which remain covalently connected by single
disulphide bond.
- After the B unit binds to the receptor of the cell
membrane, A sub unit dissociates from B sub unit
and penetrates the cell membrane. The disulphide
bond joining A1 and A2 is broken and the A1 sub unit
is activated.
24. Contd...
- The A sub unit stimulates cell bound adenylate cyclase
and adenyl cyclase activity of the cell increases , this in
turn converts ATP to cAMP in the gut epithelial cells.
- The increase c AMP level causes hype rsecretion of
electrolytes ( Na+ , K+ ) and water out of the cell and
into the lumen of the intestine.
25. Contd...
- This leads to an outporing of fluid and contains flakes
of mucus and little protein and result in vomiting
and profuse watery diarrhoea (rice water stool) .
- This result in varying degree of dehydration and
electrolyte imblance that can lead to metabolic
acidosis, hypokalaemia, shock and death in extreme
case.
29. Contd...
Clinical Features:
- The incubation period is 1-4 days for person who
develops symptoms.
- Manifest with:
. Nausea
. Vomiting
. Profuse diarrhoea
. Abdominal cramps
. Rice water stool
. Loss of fluids leads to profound dehydration,
circulatory collapse and anuria.
32. CONTD...
Transport:
If there are the chances of
delay, 2-3 gms of faeces are emulsified
in 10-15 ml VR(Venkataraman-
Ramakrishna) fluid medium or in
bile peptone transport medium or
in Cary- Blair medium.
