Water-borne Bacterial Infections Flashcards
Examples of pathogenic organisms transmitted by water:
Bacterial:
- Vibrio cholerae
- Shigella dysenteriae
2 main ways of eliminating water-borne disease:
- treatment of sewage
- purification of drinking water
Cholera 1854 John Snow
- Broad street pump accident
- cholera transmitted by faecally-contaminated water
Cholera 1883 Robert Koch
-Cholera caused by the gram-ve, motile, curved rods of the bacterium Vibrio cholerae
Epidemiology
- 7th cholera pandemic
- Patients can shed up to 10(12) organisms per day
- spread: biofilms, asymptomatic carriers
Clinical features:
incubation 2-3days, duration up to 7 days
- watery diarrhoea
- 40-60%mortality in untreated
Treatment
intravenous or oral fluid and electrolyte replacement with a simple glucose and salts solution
Pathogenesis
- 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
serotype 01
- cholera vibriosis
- classic/EI Tor biotype
non01
FREE-LIVING, NONCHOLERA VIBRIOSIS, in aquatic environments
7th pandemic
EI Tor biotype
-better survival rates
1992 outbreak due to new serotype 0139
-no cross immunity between 01 and 0139
V.cholerae is non-invasive
-symptoms mainly due to cholera toxin, an A/B subunit toxin
ZOT (zonula occludens toxin)
-affects intercellular tight junctions
Ace (accessory cholera toxin)
-causes increased transmembrane ion transport
Immunity
- surface antigens is necessary to prevent infection
- killed whole-cell vaccines are poorly effective
new oral vaccines
-better for stimulating mucosal immunity (igA antibodies)
WC/B:
heat-killed and formalin-killed cells of various serotypes and biotypes and B subunit of cholera toxin
live attenuated vaccine
-a subunit gene deleted
Shigellosis (Bacillary dysentery)
Shigella - non-motile gram-ve rods (closely related to E.coli)
Epidemiology: Sh.dysenteriae (serotype 1)
- human pathogen
- noanimal or environmantal reservoir
- high fatality rate in children
Epidemiology
shig
- low infective dose (10-100) organisms
- survives stomach acidity
Clinical features (SHIG)
- 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
Pathogenesis
- 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
Sh. dysenteriae (serotype 1)
- shiga toxin A/B toxin
- A subunit cleaves ribosomal RNA
- inhibits protein synthesis and kills target cells
- no effective vaccines
