Chapter 13 Human disease Flashcards
13.1 What pathogen causes cholera?
Vibrio cholerae
13.1 What are the symptoms of Cholera?
- Diarrhoea and therefore severe dehydration
13.1 How is cholera transmitted?
By the ingestion of water or more rearely, food that has been contaminated with faecal material containing *Vibrio cholerae *
13.1 Give a few examples of how cholera can be transmitted.
- Drinking water that isn’t properly purified
- Untreated sewage leaks into water courses
- Food contaminated by people who prepare and serve it
- Organisms (especially shellfish), have fed on untreated sewage released into rivers or the sea
13.1 Suggest three measures that can be taken to limit the spread of cholera?
- Proper personal hygiene
- Proper food hygiene
- Proper sanitation and sewage treatment
13.1 How does Vibrio cholerae cause disease?
- Surviving bacteria reach the small intestine and use their flagella to propel themselves through the mucus lining of the intestinal wall
- They then start to produce a toxic protein. It is made up of two parts, one part binds to specific carbohydrate receptors on the cell surface membrance (only epithelial cells of the small intestine have these specific receptors - explains why this is the only reigion of the body the cholera toxin affects). While the other, enters the epithelial cells causing the ion channels on the cell surface membrane to open and the chloride ions flood out of the epithelial cells and into the lumen of the intestine
- The loss of chloride ions from the epithelial cells increases its WP and decreases the WP in the lumen. This causes water to move by osmosis from the cells into the lumen
- The loss of ions from the epithelial cells establish a concentration gradient and causes ions from the surrounding blood and tissues to move into the epithelial cells by diffusion. This then establishes a WP gradient which causes water to move by osmosis from the blood and surrounding tissues into the cells
- It is this loss of water from the blood and other tissues and into the small intestine which causes the symptoms of cholera.
13.1 How is Cholera treated?
By restoring water and ions using oral rehydration therapy
13.1 Extra notes
- The domain and genus of Vibrio cholera= Eubacterium, Vibro
- Vibrio cholerae is a curved rod-shaped bacterium and is characterised by the presence of a falgellum at one end
- Some people show few if any symptoms and may act as carriers and unintentionally transmit cholera
- Almost all Vibrio cholerae bacteria ingested by humans are killed by the acidic conditions in the stomach. However, some may survive and then they cause disease.
13.2 What is diarrhoea?
- It is an intestinal disorder in which watery faeces are produced frequently
13.2 What causes diarrhoea?
- Damage to the epithelial cells lining the intestine
- Loss of microvilli due to toxins
- Excessive secretion of water due to toxins. e.g. cholera toxin
13.2 Why is only drinking water infective in treating diarrhoeal diseases?
- Water isn’t being absorbed from the intestine
- Drinking water doesn’t replace the electrolytes (ions) that are being lost from the epithelial cells of the intestine
13.2 What are the two ways of treating diarrhoea?
- It is possible to replace the water and electrolytes lost, by a drip but this requires trained personnel
- The ingredients needed can be mixed and packaged as a powder, which can be made into a solution by adding boiled water. It can be administered by people with minimal training and needs to be given regurlarly and in large amounts during the illness time period
13.2 How can the patients be rehydrated if the intestine isn’t absorbing water?
There are alternative carrier protiens on the cell-surface membrane of the epithelial cell that absorb sodium ions.
By developing a rehydration solution that uses these alternative pathways, sodium ions can be absorbed, causing the WP of the cell to drop and therefore, water moves into the cell by osmosis.
13.2 What does a oral rehydration solution need to contain and why?
- Water- to rehydrate tissues
- Sodium- to replace sodium ions lost from the epithelium of the intestine and encourage the use of the sodium-glucose transporter proteins to absorb more sodium ions
- Glucose- stimulates the uptake of sodium ions from the intestine and provides energy as it is a respiratory substrate
- Potassium- to replace potassium ions lost and to stimulate appetite
- Other electrolytes- such as, chloride and citrate ions, to help prevent electrolyte imbalance (too much or too little of an electrolyte)
13.2 Important note:
- ORS solutions doesn’t prevent or cure diarrhoea, they only rehydrate and noursih the patient untill the diarrhoea is cured by other means
