Cholera and Bacillary Dysentery

Question 1

Which of cholera and bacillary dystentery are notifiable?

Answer 1

Both are!!

Question 2

Cholera: Microbiology, source, epidemiology

Answer 2

Vibrio cholerae

• serogroups based on O antigen
• O1 and O139 responsible for pandemics; O1 El Tor in 7th pandemic (1960), O139 in 8th pandemic (1992)
• Non-agglutinating vibrios (non-O1/O139) = self limiting GE and wound infections

Source: marine environments

Question 3

Cholera: transmission, infective dose, invasive?

Answer 3

Transmission: Faecal-oral route (contaminated food/water)

Non-acid resistant: survive gastric acid by large inoculum size (high infectious dose) and protection by food
–> use of antacids or PPI increases risk of infection and lowers infectious dose

Multiply in small intestine

Attach to intestinal mucosa by pili

NON-INVASIVE

Question 4

Cholera: pathogenesis of toxin

Answer 4

Cholera toxin (enterotoxin)
- binds to enterocyte surface receptor (GM1)
- activation adenylate cyclase and increase cAMP
- increase Cl- secretion (create osmotic gradient with Na, K and water lost passively) and decrease Na/Cl reabsorption
==> massive secretion of isotonic fluid into intestinal lumen

Question 5

Cholera: clinical presentations

Answer 5

Most are asymptomatic
Acute onset of watery diarrhoea
(incubation hours - 5 days)

Severe cases (10%): vomiting, rice-like stool (mucus), dehydration –> hypovolemic shock and electrolyte imbalance –> death within 12 hrs

NO HIGH FEVER,
Little abdominal pain
Ileus and muscle cramps common

Question 6

Cholera: investigations

Answer 6

STOOL: MICROSCOPY AND CULTURE

• gram -ve curved rods
• yellow TCBS due to sucrose fermentation

(recall other characteristics: halophilic, tolerate 6% NaCl, oxidase positive, motile)

Question 7

Cholera: treatment

Answer 7

REHYDRATION
- ORS or IVF replacement if severe or can’t tolerate oral

Antibiotics (tetra/doxycycline, erythromycin/azithromycin, ciprofloxacin) NOT ESSENTIAL

• reduce volume of diarrhoea
• decrease vibrio excretion by 1 day as infection control measures in outbreak

Question 8

Cholera: prevention

Answer 8

WASH (water sanitation, hygiene)
Proper waste disposal
Surveillance

Vaccines - generally not indicated

• -> 2 oral-killed doses for travellers to endemic areas
• -> but limited efficacy and short duration

Question 9

Dysentery definition

Answer 9

Frequent passing of stool with blood and mucus, along with painful defecation

Can be amoebic or bacillary
Bacillary can be shigella or invasive strains of E. coli (generally refers to shigella)

Question 10

Shigella dysentery: microbiology

Answer 10

Shigella species (47 seroptypes in 4 groups)

S. dysenteriae - most pathogenic
S. flexneri
S. boydii
S. sonnei - least pathogenic

Enterobacteriaceae, non-motile (c.f. E. coli and salmonella, non-lactose fermenter c.f. E. coli)

Question 11

Shigella dysentery: pathogenesis - transmission, infective dose, invasive?, toxin

Answer 11

Transmission: faecal-oral route (contaminated food/water, human-to-human)

Gastric acid resistant: low infective dose of 10-100 bacteria

INVADES enterocytes, multiplies and destroys intestinal mucosa –> colonic ulceration and mucosal abscesses

Shiga toxin (enterotoxin and cytotoxic)
--> binds to GB3 receptor on intestinal mucosa --> cause cell death and vascular injury 

Rarely invades systemically

Question 12

Shigella dysentery: clinical presentations

Answer 12

Incubation period: 1-7 days

Diarrhea with blood and mucus (50-80%)
Fever, abdominal pain, vomiting

DISEASE OF CHILDREN (<5yrs)

Question 13

Shigella dysentery: investigation

Answer 13

STOOL CULTURE

rarely require blood culture

Question 14

Shigella dysentery: treatment

Answer 14

Rehydration
ANTIBIOTICS INDICATED – lower excretion and decrease duration of symptoms (as there is high risk of spread with low infective dose c.f. cholera)
–> fluoroquinolone, 3rd gen cephalosporin (ceftriaxone), azithromycin, septrin

Question 15

Shigella dysentery: prevention

Answer 15

No vaccine

Clean food and water, proper waste disposal, sanitation
Infection Control

Question 16

Escherichia coli infections: strains, source

Answer 16

Only certain strains cause diarrhoea
- EPEC, ETEC (traveller’s diarrhoea), EIEC (can also cause dysentery), EHEC

O157:H7 EHEC/ verotoxigenic E. coli

• • found in GIT on CATTLE - GROUND BEEF
• • hamburgers as common source

O104:H4 recent outbreak in Germany due to sprouts

Question 17

E. coli diarrhoea: pathogenesis

Answer 17

Human-to-human transmission

EHEC
- bloody diarrhoea by Shiga-like toxin (verotoxin) with similar mechanism as shigella – toxigenic and haemorrhagic

ETEC
- traveller’s diarrhoea with heat labile toxin similar to that of cholera toxin (mild to severe diarrhoea)

Question 18

EHEC: clinical presentations

Answer 18

Watery diarrhoea, fever, vomiting

Haemorrhagic colitis in elderly (bloody diarrhoea)

HUS in children: triad of HA, thrombocytopenia (thrombotic microangiopathy) and AKI; mortality 3-5%

Question 19

EHEC: treatment

Answer 19

Supportive: rehydration

ANTIBIOTICS CONTRAINDICATED - increase the release of verotoxin and shedding period –> precipitate HUS

Question 20

General investigations and management of Dysentery

Answer 20

STOOL

• microscopy for ova, cysts, RBC, WBC
• culture on selective media
• modified acid-fast stain for parasites

Blood
- rarely culture in severe cases e.g. shigella in HIV patients

NOTIFICATION OF DOH

Outbreak:

• identify source and travel history
• culture suspected food
• contact precautions (enteric isolation - prevent spread by contact with faeces or vomit e.g. room, cohort, PPE, disinfection)

Treatment:

• FLUID AND ELECTROLYTE replacement (ORT, IV if severe or vomiting)
• Antibiotics not routine (only with systemic involvement, in shigella infection or for control in outbreaks in non-endemic countries; C/I in EHEC!!)