Download 06_-_Cholera

Cholera
Cholera
A life-threatening secretory diarrhea
induced by enterotoxin secreted by
V. cholerae ( non-invasive)
Water-borne illness caused by
ingesting water/food contaminated
by copepods infected by V. cholerae
A major epidemic disease
V. cholerae
Transmitted by fecal-oral route
Endemic in areas of poor sanitation
(India and Bangladesh )
May persist in shellfish or plankton
7 pandemics since 1817 – first 6 from
Classical strains, 7th from El Tor
Cholera is not transmissible personto-person, but can easily be spread
through contaminated food and water
People Most at Risk
People with low gastric acid levels
Children: 10x more susceptible than
adults
Elderly
Blood types
O>> B > A > AB
Incubation Period
• Ranging from a few hours to 5 days
• Most cases presenting within 1-3 days
• As expected for organisms passing through the
gastric barrier, the incubation period is shortest
when:
• highest dose of ingested organsim
• High gastric pH
• Infectious dose ranges from 106_ 1011 colonizing units
Symptoms
Occur 2-3 days after consumption of
contaminated food/water
Usually mild, or no symptoms at all
75% asymptomatic
20% mild disease
2-5% severe
Vomiting
Cramps
Watery diarrhea (1L/hour)
Without treatment, death in 18 hoursseveral days
Cholera Gravis
More severe symptoms
Rapid loss of body fluids
6 liters/hour
107 vibrios/mL
Rapidly lose more than 10%
of bodyweight
Dehydration and shock
Death can occur within 2-3
hours
Consequences of Severe
Dehydration
Intravascular volume
depletion
Severe metabolic
acidosis
Hypokalemia
Cardiac and renal failure
Sunken eyes, decreased
skin turgor
Almost no urine
production
Mortality
• In untreated patients, mortality can reach 5070%
• Risk much higher in children
• 10x greater than adults
• As well as pregnant women
• 50% risk of fetal death in 3rd trimester
• Patients can die within 2-3 hours of first sign
of illness also seen from 10 hours- several
days
Diagnosis
No clinical manifestations help
distinguish cholera from other causes
of severe diarrhea:
Enterotoxigenic e. coli
Viral gastroenteritis
Bacterial food poisoning
Laboratory Diagnosis
• Made through isolation of bacteria from stool
samples
• Specimens are collected
• Gram Stain show sheets of curved Gram negative
rods
• Untreated patients have 106 to 108 organisms / mL of
stool
• Important to start treatment before the cause of
infection is identified: death can occur within
hours
Labroratory Diagnosis Cont.
Vibrios often detected by dark field
microscopy of stool
 Organisms are motile, appearing like
“shooting stars”
 When plated on sucrose dishes, yellow
colonies appear confirming cholera
 Additional methods of detection include
PCR and monoclonal antibody-based stool
tests.

Treatment
• Three options prove most effective:
• Oral Rehydration
• Intravenous Rehydration
• Antimicrobial Therapy
Treatment: Oral Rehydration
Salts (ORS)
Reduces mortality from
over 50% to less than
1%
O.R.S.
• The WHO recommends a solution
containing:
•
•
•
•
3.5 g NaCl
2.9 g trisodium citrate/ NaHCO3
1.5 g KCl
20 g glucose or 40 g sucrose
• Per liter of water
• Min. of 1.5 x the stool volume losses should be
administered
• Commercially sold over-the-counter
Intravenous Rehydration
•
•
Used in patients who lost more than
10% of body weight from diarrhea or
are unable to drink due to vomiting
Ringer’s Lactate is usually used in
hospitals.
Intravenous Rehydration –
Additional Options
•
Saline can be used, however bicarbonate and
potassium losses are not being replaced
Antimicrobial Therapy
Seen as an adjunct to appropriate rehydration
• Reduce the volume of diarrhea by a half and the
duration of excretion to about 1 day, therefore,
they lower the expense of treatment and play a
role in cholera control.
• Due to short duration of illness, antibiotics not
highly recommended
•
Dosage – Antibiotic Agents
Given orally when vomiting
stops.
• Tetracycline is the standard
treatment
• Administered in single dose
primarily to prevent spread
of secondary infection
•
WHO guidelines
Prevention
V. Cholerae is spread through contaminated
food and water, therefore, prevention
depends upon the interruption of fecal-oral
transmission
• Antibiotic prophylaxis, vaccines and
surveillance of new cases are the answer to
preventing the spread of disease.
•
Antibiotic prophylaxis
The WHO recommends prophylaxis if 1
household member in a family becomes ill.
• Mass administration of antibiotics to a whole
community is not effective nor recommended
•
Vaccines
•
Two types :
– Killed-whole-cell formulation:
Provides immunity to only 50% of adult
victims and to less than 25% of children
– Live-attenuated vaccine, geneticallyengineered
Provides >90% protection against classical
biovar and 65-80% against El-Tor biovar.
Traveling Precautions
Boil or treat water with chlorine or
iodine
No ice
Cook everything
Rule of thumb: “Boil it, cook it, peel
it, or forget it.”
Wash hands frequently