CholeraLearning Objectives• know that the cholera bacterium is an

example of a prokaryotic organism• Identify and label parts of a

prokaryotic cell. • understand how the cholera

bacterium causes symptoms of cholera

What do you know about cholera?

Discuss in pairs.

General Background• Infectious gastroenteritis

• Caused by bacterium vibrio cholerae

• Transmitted to humans through ingesting contaminated water or food

• Outbreaks are common in war zones, refugee camps, and places where people live close together in squalid conditions

Symptoms

Symptoms include• acute severe watery diarrohea (milky in colour –

appearance of rice)• Rapid dehydration• Rapid pulse• Dry skin• Tiredness• Nausea• Abdominal cramps• Vomiting

Cholera bacterium- example of a prokaryotic organism

Two types of organism - prokaryotic - eukaryoticProkaryotic cells• lack nucleus• DNA floats loosely in centre of cell• Most common form of life on earth• Divide and reproduce by simple mitosis

Prokaryotic cell

• Cell wall – protection and support• Plasma membrane – regulates exchange of

nutrients and oxygen• DNA – circular strand, floats free in cytoplasm• Cytoplasm – provides suitable environment• flagella –hair like structure, functions in movement• Plasmid – extra Chromosomal DNA,contains genes for antibiotic resistance

Effect of cholera toxin

• Cholera bacteria produce a toxin• chloride ion protein channels open in plasma

membrane of intestinal epithelial cells• Chloride ions move into lumen• Decreases water potential of liquid in lumen• Water moves out of blood, across epithelial cells

and into lumen by osmosis• Massive increase in water secretion into lumen –

diarrohea and dehydration

Effect of cholera toxin

Cell diagram

Task

• Explain how infection with cholera bacterium leads to watery diarrhoea and dehydration.

• Explain why cholera is more prevalent in developing countries.

• Name three organelles found in a prokaryotic cell and give their function.

Plenary

What is the difference between a prokaryotic and eukaryotic cell?

Can you label the structure of a prokaryotic cell?

What function does a flagellum play?

What is the cell wall made from?

How does the cholera toxin produce watery diarrohea?

Learning objectives

• Know how cholera is treated

• Understand the implications of scientific research into treatment

• Think about ethical implications of clinical testing

Treatments of cholera

Replacing fluid lost through diarrhoea is vital

Two options for replacing fluid

- intravenous drip

- oral re-hydration solutions

What might be the problem with using i.v. drips in developing countries?

Oral Re-hydration Solutions (ORS)

• Solution contains - large amounts of salts ( sodium and

chloride ions) - large amounts of sugars (glucose and sucrose all dissolved in water.

Sodium ions – increase glucose absorption (co- transported in epithelial cells)

Oral Rehydration solutions

• Getting the concentration is essential for effective treatment

(home made treatment – 8 teaspoons of sugar, 1 teaspoon of salt mixed in 1 litre of water)

• ORS should be taken in frequent, small amounts• Benefits include

- cheap treatment

- easy to administer

- easy to package and distribute to wide areas

Research into new ORS

• ORS vital in treating diarrhoeal disease

• Research into new improved ORS always being carried out

What do scientists have to do before a new treatment can be put onto the market?

Brainstorm

How can scientists prove that treatments are more effective and safe for humans?

Clinical testing on humans.

Is this right?

What ethical issues might be associated with trialling ORS

Ethical issues

• Diarrhoeal diseases mostly affect children – many trials involve children

• Parents decide if child will participate – child has no choice

• Treatment must be trialled on children to prove effectiveness

• Clinical trials involve blind trial – patients don’t know which treatment they are taking – standard or new ORS

• Blind trials eliminate bias that might skew the data (placebo)

Ethical issues

• When a new ORS is first trialled scientists cannot be sure that it will be better than current treatment

• Risk of patient dying when original better treatment was available.

Do patients have the right to know about and decide on which treatment they have?

Task

• Name three reasons why ORS used in treatment of cholera in developing countries.

• Explain why scientist have to perform clinical tests on any new treatments.

• Why are blind trials carried out and what are the ethical issues associated with this?

Homework

• Explain how infection with the cholera bacterium leads to diarrhoea

• Give one argument for and one argument against trialling new oral re-hydration solutions on children