Water-borne infections Flashcards
What are the public health measures to prevent water-borne infections?
Treatment of sewage
Treatment of drinking water
Will eliminate or reduce most water-borne disease
What is cholera responsible for?
The foundation of the science of epidemiology and for start of public health measures to control disease
How many organisms are shed a day in someone with cholera?
10 (power 12) organisms a day
Who does vibrio cholerae infect?
Infects only man
How does vibrio cholerae?
Environmental survival (fresh and salt water) biofilms Short-term, asymptomatic carriers
What is the main infectious serotype of v. cholerae?
Serotype O1
How many pandemics has there been of cholera?
7
What are the clinical features of cholera?
Incubation 2-3 days, duration up to 7 days
Profuse watery diarrhoea (rice-water stools) up to 20 L/day
40-60% mortality if untreated, <1% if treated
How is cholera treated?
Intravenous or oral fluid and electrolyte replacement with a simple glucose and salts solution
Is v. cholerae invasive?
No
Sits on epithelial and produces a AB subunit toxin
What is the A/B subunit toxin encoded by?
CTX phage- intestinal colonisation factor TCP
What is A1?
A1 is ADP-ribosyl transferase, transfers ADP-ribose moiety from NAD to G protein Gs
What does A1 activate?
Activates host cell adenylate cyclase giving high levels of cAMP from ATP
What type of signal is cAMP?
Intracellular
What does cAMP cause?
Causes active secretion of Cl- Decreased absorption of Na+ and Cl-
Massive loss of water and electrolytes from body
What are additional toxins?
Zot (Zonula occludens toxins)
Ace (Accessory cholera toxin)
What does Zot affect?
Intracellular tight junctions
What does Ace cause?
Increased transmembrane ion transport
How is infection prevented in cholera?
Both cholera toxin and bacterial surface antigens are necessary
What are the new oral vaccines for cholera?
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
What is shigella?
Non-motile Gram-negative rods (closely related to E. coli)
How severe is shigella sonnei?
Usually mild disease
How severe is Sh. Flexneri, Sh. Boydii?
More severe
How severe is Sh. Dysenteriae?
Most severe
How is shigellosis spread?
Person to person
Who does shigellosis primarily affect?
Primarily a disease of children and the elderly
What is Sh. Dysenteriae (serotype 1)?
Mainly associated with epidemics in developing countries
Affects all ages
High fatality rate in children
What are the clinical features of shigellosis?
Incubation 1-4d, duration 5-7d
Diarrhoea with blood and mucus, abdominal cramps, fever
Dehydration may be severe
Frequent complication: kidney damage in S. dysenteriae infections (vero toxin)
What’s the treatment of shigellosis?
Oral rehydration therapy
Antibiotics only given in severe cases
Antibiotic resistance is common and plasmid-mediated
How does shigellosis cause disease?
Organisms attach to, invade and destroy the cells of the mucosal epithelium of the distal ileum and colon, causing inflammation and ulceration
What happens in shigellosis when bacteria is taken up by M cells of the Peyer’s patches?
Then invade the mucosal epithelial cells
Escape from the phagosome into the cytoplasm
Multiply rapidly
Spread from cell to cell via actin filaments
What vaccines are there for shigellosis?
No effective vaccines
