Water-borne Bacterial Infections

Question 1

Examples of pathogenic organisms transmitted by water:

Answer 1

Bacterial:

• Vibrio cholerae
• Shigella dysenteriae

Question 2

2 main ways of eliminating water-borne disease:

Answer 2

• treatment of sewage

- purification of drinking water

Question 3

Cholera 1854 John Snow

Answer 3

• Broad street pump accident

- cholera transmitted by faecally-contaminated water

Question 4

Cholera 1883 Robert Koch

Answer 4

-Cholera caused by the gram-ve, motile, curved rods of the bacterium Vibrio cholerae

Question 5

Epidemiology

Answer 5

• 7th cholera pandemic
• Patients can shed up to 10(12) organisms per day
• spread: biofilms, asymptomatic carriers

Question 6

Clinical features:

Answer 6

incubation 2-3days, duration up to 7 days

• watery diarrhoea
• 40-60%mortality in untreated

Question 7

Treatment

Answer 7

intravenous or oral fluid and electrolyte replacement with a simple glucose and salts solution

Question 8

Pathogenesis

Answer 8

• large infective dose required
• 10(9) -10(11) organisms
• rapidly killed by gastric activity
• colonisation of small intestine depends on motility, production of mucinase (protease), TCP (toxin-co-regulated pilus) adhesin

Question 9

serotype 01

Answer 9

• cholera vibriosis

- classic/EI Tor biotype

Question 10

non01

Answer 10

FREE-LIVING, NONCHOLERA VIBRIOSIS, in aquatic environments

Question 11

7th pandemic

Answer 11

EI Tor biotype

-better survival rates

Question 12

1992 outbreak due to new serotype 0139

Answer 12

-no cross immunity between 01 and 0139

Question 13

V.cholerae is non-invasive

Answer 13

-symptoms mainly due to cholera toxin, an A/B subunit toxin

Question 14

ZOT (zonula occludens toxin)

Answer 14

-affects intercellular tight junctions

Question 15

Ace (accessory cholera toxin)

Answer 15

-causes increased transmembrane ion transport

Question 16

Immunity

Answer 16

• surface antigens is necessary to prevent infection

- killed whole-cell vaccines are poorly effective

Question 17

new oral vaccines

Answer 17

-better for stimulating mucosal immunity (igA antibodies)

Question 18

WC/B:

Answer 18

heat-killed and formalin-killed cells of various serotypes and biotypes and B subunit of cholera toxin

Question 19

live attenuated vaccine

Answer 19

-a subunit gene deleted

Question 20

Shigellosis (Bacillary dysentery)

Answer 20

Shigella - non-motile gram-ve rods (closely related to E.coli)

Question 21

Epidemiology: Sh.dysenteriae (serotype 1)

Answer 21

• human pathogen
• noanimal or environmantal reservoir
• high fatality rate in children

Question 22

Epidemiology

shig

Answer 22

• low infective dose (10-100) organisms

- survives stomach acidity

Question 23

Clinical features (SHIG)

Answer 23

• incubation 1-4d, duration 5-7d
• diarrhoea with blood and mucous
• treatment =oral rehydration therapy
• antibiotics only given in severe cases
• ab resistance=common and plasmid-mediated

Question 24

Pathogenesis

Answer 24

• organisms attach to mucosal epitheliam of the distal ileum and colon causing inflammation and ulceration
• bacteria first taken up by M cells of the Peyer’s patches then invade mucosal epithelial cells

Question 25

Sh. dysenteriae (serotype 1)

Answer 25

• shiga toxin A/B toxin
• A subunit cleaves ribosomal RNA
• inhibits protein synthesis and kills target cells
• no effective vaccines