VIBRIO CHOLERAE
Cholera, caused by Vibrio cholerae serotype 01, is the
archetype bacterial cause of acute watery diarrhoea.
Following its origin in the Ganges valley, devastating
epidemics have occurred, often in association with
large religious festivals, and pandemics have spread
world-wide. The seventh pandemic, due to the El Tor
biotype, began in 1961 and spread via the Middle East
to become endemic in Africa. In 1990 it reached Peru
and spread throughout South and Central America.
Since August 2000 there has been a massive outbreak
in South Africa. El Tor is more resistant than classical
Vibrio, and causes prolonged carriage in 5% of
infections. A new classical toxigenic strain, serotype
0139, established itself in Bangladesh in 1992 and
started a new pandemic.
Infection spreads via the stools or vomit of
symptomatic patients or of the much larger number of
subclinical cases. It survives for up to 2 weeks in fresh
water and 8 weeks in salt water. Transmission is
normally through infected drinking water, shellfish
and food contaminated by flies, or on the hands of
carriers.
Clinical features
Severe diarrhoea without pain or colic begins suddenly
and is succeeded by vomiting. Following the
evacuation of normal gut faecal contents, typical 'rice-
water' material is passed consisting of clear fluid with
flecks of mucus. Classical cholera produces enormous
loss of fluid and electrolytes, leading to intense
dehydration with muscular cramps. Shock and oliguria
develop but mental clarity remains. Death from acute
circulatory failure may occur rapidly unless fluid and
electrolytes are replaced. Improvement is rapid with
proper treatment.
The majority of infections, however, cause mild illness
with slight diarrhoea. Occasionally, a very intense
illness, 'cholera sicca', occurs, with loss of fluid into
dilated bowel, killing the patient before typical
gastrointestinal symptoms appear. The disease is more
dangerous in children.
Clinical diagnosis is easy during an epidemic.
Otherwise the diagnosis should be confirmed
bacteriologically. Stool dark field microscopy shows
the typical 'shooting star' motility of V. cholerae.
Rectal swab or stool cultures allow identification.
Cholera is notifiable under international health
regulations.
Management
Maintenance of circulation by replacement of water
and electrolytes is paramount. Early intervention
improves prognosis. A clinical assessment of
dehydration is made from the appearance of the
patient. Oral rehydration solution (ORS) is effective
and safe for all but the most severely dehydrated
patients. The addition of resistant starch to ORS
reduces faecal fluid loss and shortens the duration of
diarrhoea in adolescents and adults with cholera.
The effect is caused by enhanced sodium absorption in
the colon due to short-chain fatty acids produced in
the colon from non-absorbed carbohydrates. Ringer-
Lactate is the best fluid for intravenous replacement.
Vomiting usually stops once the patient is rehydrated,
and fluid should then be given orally up to 500 ml
hourly. The fluid required is calculated every 8 hours
from the urine volume, stool and vomit output, and
estimated insensible loss (as much as 5 litres/24 hours
in a hot humid climate). Total fluid requirements may
exceed 50 litres over a period of 2-5 days. Accurate
records are greatly facilitated by the use of a 'cholera
cot' which has a reinforced hole under the patient's
buttocks beneath which a graded bucket is placed.
In children careful attention to fluid balance is
required; they are prone to hypoglycaemia. Three days'
treatment with tetracycline 250 mg 6-hourly, a single
dose of doxycycline 300 mg or ciprofloxacin 1 g in
adults all reduce the duration of excretion of Vibrio
and the total volume of fluid needed for replacement.
Prevention
Strict personal hygiene is vital and drinking water
should come from a clean piped supply or be boiled.
Flies must be denied access to food. Parenteral
vaccination with a killed suspension of V. cholerae may
provide limited protection. Oral vaccines containing
killed V. cholerae and the B subunit of cholera toxin
are available but are of limited efficacy.
In epidemics public education, and control of water
sources and population movement are vital. Mass
single-dose vaccination and treatment with
tetracycline are valuable. Disinfection of discharges
and soiled clothing, and scrupulous hand-washing by
medical attendants reduce the danger of spread.
VIBRIO PARAHAEMOLYTICUS
This marine organism produces a disease similar to
enterotoxigenic E. coli. It is acquired from raw seafood
and is very common where ingestion of such food is
widespread (e.g. Japan). After an incubation period of
approximately 20 hours, explosive diarrhoea,
abdominal cramps and vomiting occur. Systemic
symptoms of headache and fever are frequent but the
illness is self-limiting, taking 4-7 days to resolve.
Rarely, a severe septicaemic illness arises. If Vibrio
infection of this nature is suspected, the laboratory
ought to be notified since specific halophilic culture
requirements apply.
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