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10.3Diseases and Immunity

Cholera — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

5 min read 9 parts Lesson 3 of 3 1 quiz

📚 Cambridge IGCSE Biology 0610 Hub / Topical Revision
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Lesson summary

10.3 Cholera — IGCSE BIOLOGY notes: Explain how Vibrio cholerae causes diarrhoea and how cholera is spread, prevented and treated (Supplement).Diarrhoea — The loss of watery faeces from the anus.Danger — Severe, long diarrhoea can cause death.Effect — Large losses of water and io…

  • Dehydration
  • Loss of salts
  • Oral rehydration therapy
  • Severe cases
  • Antibiotics
  • Water potential

Part 1 of 7Diarrhoea

Diarrhoea
  • The loss of watery faeces from the anus.
Danger
  • Severe, long diarrhoea can cause death.
Effect
  • Large losses of water and ions stop tissues and organs working properly.
Causes
  • There are many, one of which is infection with Vibrio cholerae, which causes cholera.

Part 2 of 7How cholera causes diarrhoea

1
The bacteria enter in infected water or food and attach to the wall of the small intestine.
2
They produce a toxin.
3
The toxin stimulates the cells lining the intestine to release chloride ions into the lumen.
4
The chloride ions accumulate and lower the water potential in the lumen.
5
Once it is lower than in the lining cells, water moves out of the cells into the intestine by osmosis.
6
Large quantities of water are lost from the body in watery faeces.
7
The blood is left with too little water and chloride ions.

Part 3 of 7Transmission

Source
  • Infected people pass large numbers of bacteria in their faeces.
Spread
  • Untreated sewage reaches rivers, wells or pipes and people drink or eat contaminated water or food.
Flies
  • Houseflies can carry bacteria from faeces to food.
Outbreaks
  • They are common after floods, wars and disasters when sanitation breaks down.

Part 4 of 7Symptoms

Diarrhoea
  • Sudden severe watery diarrhoea.
Dehydration
  • Vomiting, extreme thirst, dry mouth and sunken eyes.
Loss of salts
  • Muscle cramps and weakness.
Untreated
  • Low blood volume can lead to shock and death.

Part 5 of 7Treatment

Oral rehydration therapy
  • A drink with a small amount of salt and sugar dissolved in it.
  • It replaces water and ions lost, and glucose helps the intestine absorb sodium ions and water.
Severe cases
  • Fluids may be given directly into a vein.
Antibiotics
  • They kill the bacteria and shorten the illness.

Part 6 of 7Prevention

MeasureHow it helps
Clean water supplyWater free of pathogens prevents waterborne disease
Sewage treatmentStops faeces contaminating water supplies
Hand washing with soapRemoves bacteria before they reach food or the mouth
Hygienic food preparationCooking food and covering it keeps bacteria and flies away
VaccinationAvailable for people at high risk

Part 7 of 7More from the specification

More from the specification
Immune
  • Able to destroy a pathogen before it causes disease.
Active immunity
  • Immunity from making your own antibodies and memory cells.
Passive immunity
  • Short-term immunity from antibodies given by another individual.
Transmissible disease
  • A disease in which the pathogen can be passed from one host to another.
Antibody
  • A protein made by lymphocytes that binds to a specific antigen.
Immunity
  • Protection from a disease through memory cells.
Antigen
  • A molecule on the surface of a cell that lymphocytes can recognise.
Lymphocyte
  • White blood cell that produces antibodies.
Specific
  • Able to act on only one type of substrate.
Barrier
  • A structure that prevents pathogens from entering.
Population
  • A group of organisms of one species in the same area at the same time.

Key terms

TermMeaning
CholeraA disease caused by Vibrio cholerae bacteria that causes severe diarrhoea.
DiarrhoeaThe loss of watery faeces from the anus.
ToxinA poison released by bacteria.
Water potentialThe tendency of water to move; lowered by dissolved ions.
Oral rehydration therapyA drink of water with a little salt and sugar that replaces lost water and ions.
OsmosisNet movement of water from higher to lower water potential through a partially permeable membrane.

Avoid these mistakes

1
Saying the bacterium itself causes the loss of water — its toxin releases chloride ions that draw water out by osmosis.
2
Saying chloride ions raise water potential in the gut — they lower it.
3
Treating cholera with antibiotics only — rehydration to replace water and ions is the key treatment.
4
Saying cholera spreads through the air — it spreads in contaminated water and food.

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