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Infection and Immunity > Water-borne infections > Flashcards

Water-borne infections Flashcards

1
Q

What are the public health measures to prevent water-borne infections?

A

Treatment of sewage
Treatment of drinking water
Will eliminate or reduce most water-borne disease

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2
Q

What is cholera responsible for?

A

The foundation of the science of epidemiology and for start of public health measures to control disease

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3
Q

How many organisms are shed a day in someone with cholera?

A

10 (power 12) organisms a day

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4
Q

Who does vibrio cholerae infect?

A

Infects only man

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5
Q

How does vibrio cholerae?

A 
Environmental survival (fresh and salt water) biofilms
Short-term, asymptomatic carriers
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6
Q

What is the main infectious serotype of v. cholerae?

A

Serotype O1

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7
Q

How many pandemics has there been of cholera?

A

7

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8
Q

What are the clinical features of cholera?

A

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

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9
Q

How is cholera treated?

A

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

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10
Q

Is v. cholerae invasive?

A

No

Sits on epithelial and produces a AB subunit toxin

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11
Q

What is the A/B subunit toxin encoded by?

A

CTX phage- intestinal colonisation factor TCP

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12
Q

What is A1?

A

A1 is ADP-ribosyl transferase, transfers ADP-ribose moiety from NAD to G protein Gs

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13
Q

What does A1 activate?

A

Activates host cell adenylate cyclase giving high levels of cAMP from ATP

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14
Q

What type of signal is cAMP?

A

Intracellular

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15
Q

What does cAMP cause?

A

Causes active secretion of Cl- Decreased absorption of Na+ and Cl-
Massive loss of water and electrolytes from body

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16
Q

What are additional toxins?

A

Zot (Zonula occludens toxins)

Ace (Accessory cholera toxin)

17
Q

What does Zot affect?

A

Intracellular tight junctions

18
Q

What does Ace cause?

A

Increased transmembrane ion transport

19
Q

How is infection prevented in cholera?

A

Both cholera toxin and bacterial surface antigens are necessary

20
Q

What are the new oral vaccines for cholera?

A

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

21
Q

What is shigella?

A

Non-motile Gram-negative rods (closely related to E. coli)

22
Q

How severe is shigella sonnei?

A

Usually mild disease

23
Q

How severe is Sh. Flexneri, Sh. Boydii?

A

More severe

24
Q

How severe is Sh. Dysenteriae?

A

Most severe

25
Q

How is shigellosis spread?

A

Person to person

26
Q

Who does shigellosis primarily affect?

A

Primarily a disease of children and the elderly

27
Q

What is Sh. Dysenteriae (serotype 1)?

A

Mainly associated with epidemics in developing countries
Affects all ages
High fatality rate in children

28
Q

What are the clinical features of shigellosis?

A

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)

29
Q

What’s the treatment of shigellosis?

A

Oral rehydration therapy
Antibiotics only given in severe cases
Antibiotic resistance is common and plasmid-mediated

30
Q

How does shigellosis cause disease?

A

Organisms attach to, invade and destroy the cells of the mucosal epithelium of the distal ileum and colon, causing inflammation and ulceration

31
Q

What happens in shigellosis when bacteria is taken up by M cells of the Peyer’s patches?

A

Then invade the mucosal epithelial cells
Escape from the phagosome into the cytoplasm
Multiply rapidly
Spread from cell to cell via actin filaments

32
Q

What vaccines are there for shigellosis?

A

No effective vaccines

Infection and Immunity (23 decks)

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