11: Cholera

Question 1

why is cholera different from everything else we’ve looked at?

Answer 1

only bacterium we take about

Question 2

what is the cholera epidemic thought to be?

Answer 2

beginning of the study of epidemiology

also important because it caused epidemics for a very long time

Question 3

serotypes

Answer 3

based on antibodies to the antigen on the surface of cholera

differentiated based on ability of antibodies to recognise different O antigens
- only O1 and O139 have been found to cause widespread human disease/pandemics

comes from serum antibodies positive for that type

Question 4

biotypes

Answer 4

serotypes like O1 can be further separated into biotypes

based on results of biological tests

what we will look at is classic and el tor

Question 5

where is cholera heavily endemic?

Answer 5

Bangladesh

attack rate low in adults compared to children
- disease of children in Bangladesh but disease of everyone else in non-endemic areas

Question 6

cholera prevention

Answer 6

good sanitation and clean water

Question 7

pandemics of cholera since the 1800s

Answer 7

1. 1816-1826
   - Bengal, India, China
2. 1829-1851
   - London, Paris, Russia and North America
3. 1852-1860
   - Russia had over a million deaths
   - biggest one yet
4. 1863-1875
   - Europe, Africa, etc.
5. 1881-1896
   - Germany, last serious outbreak in Europe
6. 1899-1923
   - Russia, Africa
7. 1961-present

first 6 of the classic serotype and now el tor

Question 8

uniqueness of cholera pandemic

Answer 8

slowest one ever

Question 9

seasonality?

Answer 9

comes in waves (not necessarily just once a year)

seasonality that comes and goes in Bangladesh

Question 10

environmental reservoir

Answer 10

fact that cholera bacteria lives on small animals in the water

bacteria can still grow and replicate outside of humans and also in the absence of animals even if they stay attached to animals mostly

seasonality has to due with things in the environment and then contact with humans

Question 11

does cholera damage environmental reservoir?

Answer 11

no damage made to host

just live on the outer surface like bacteria on our skin/gut

Question 12

why is cholera not a virus?

Answer 12

extracellular bacteria that causes disease in the small intestine

doesn’t affect cells like a virus

Question 13

immune reaction to cholera

Answer 13

intestinal IgA antibody can prevent attachment of the bacteria to the mucosal surface and neutralise/prevent binding of the enterotoxin
- blocks them from being attached to the intestine wall so they get washed out

also other antibodies that bind to the toxin and prevent it from binding to epithelial cells and squeezing water out

Question 14

where does cholera disease come from?

Answer 14

cholera toxin (CT) which triggers release of fluid from muscosal epithelial cells lining the GI tract and causes diarrhoea
- diarrhoea beneficial for cholera to pass to next host

CT acts on epithelial cells making them secrete all their water
- individuals die of dehydration from severe diarrhea

Question 15

cholera treatment

Answer 15

usually oral rehydration solution (ORS)
- contains glucose, sodium chloride, potassium chloride and trisodium citrate

electrolytes and sugar to allow you to recover from electrolyte imbalance

Question 16

cholera toxin phage

Answer 16

phage as a virus infecting cholera and carrying genes encoding for CT

infects bacteria, stays there and replicates with bacteria to produce the toxin protein

without the phage, cholera does not cause severe disease/death in humans

virulence factor that can be transferred to different cholera types
- phage can carry CT from one cholera serotype to another (creating a new wave of human infections)

Question 17

cholera vaccines

Answer 17

three pre-qualified oral vaccines (OCV) by WHO
- Dukoral, Shanchol, Euvichol-Plus

all heat inactivated vaccines containing whole bacteria

not highly effective and offer incomplete protection