Cholera is an acute intestinal infection caused by the bacterium Vibrio cholerae Despite being an avoidable and treatable condition, cholera kills over 100,000 individuals each year The main source of infection is contaminated water and food, with most cases occurring in developing countries The incubation period for cholera is short (less than one to five days); the bacteria multiply in the intestine where they release a powerful enterotoxin that produces severe inflammation of the intestine, causing a copious, watery diarrhoea to be produced

The main source of cholera infection is water contaminated by the faeces of sufferers and carriers; the bacterium is also spread by contaminated food Cholera is most prevalent in countries where access to safe water and sanitation measures is inadequate

Number of Cholera Cases The data below displays the cholera cases and deaths notified to the World Health Organisation (WHO) in 2003 Country/Area Number of Cholera Cases Log Number of Cases Deaths Africa 108 067 1884 Americas 33 Asia 3 463 10 Europe 12 Determine the log values for the number of cholera cases and display your data as a bar chart; comment on the world distribution of cholera and the number of reported deaths for the disease Oceania data was not reported in 2003

Number of Cholera Cases The data below displays the cholera cases and deaths notified to the World Health Organisation (WHO) in 2003 Country/Area Number of Cholera Cases % resulting in death Deaths Africa 108 067 1.74 1884 Americas 33 0.00 Asia 3 463 0.28 10 Europe 12 Determine the % for the number of cholera cases and display your data as a bar chart; comment on the world distribution of cholera and the number of reported deaths for the disease Oceania data was not reported in 2003

Number of Cholera Cases The data below displays the cholera cases and deaths notified to the World Health Organisation (WHO) in 2003 Country/Area Number of Cholera Cases Log Number of Cases Deaths Africa 108 067 5.03 1884 Americas 33 1.52 Asia 3 463 3.54 10 Europe 12 1.08 12 cases of cholera were reported in Europe where access to safe water and sanitation provision is good. How do you account for these cases?

Number of Cholera Cases All 12 cases occurring in Europe were imported The data below displays the cholera cases and deaths notified to the World Health Organisation (WHO) in 2003 Country/Area Number of Cholera Cases Log Number of Cases Deaths Africa 108 067 5.03 1884 Americas 33 1.52 Asia 3 463 3.54 10 Europe 12 1.08 All 12 cases occurring in Europe were imported

Comma-shaped bacterium (vibrio) Haemagglutinin Accessory colonisation factors Comma-shaped bacterium (vibrio) Flagellum Pili Flagellar motility and chemotaxis allow the bacteria to colonise the small intestine; bacteria swim into the intestinal mucosal layer The haemagglutinins, accessory factors and pili are required for adherence to and successful colonisation of intestinal epithelial cells Enterotoxin release disturbs normal gut homeostasis

Transmission electron microscope image of Vibrio cholerae that has false digital colour. This is a wild type strain, clearly showing the pili as 7 nm fibres that form bundles.

Normal Gut Homeostasis Within the human intestine, normal movement of ions involves the uptake of sodium ions from food into the bloodstream; there is no net movement of chloride ions from the blood into the lumen of the intestine Na+ from food When Vibrio cholerae colonise the intestine, normal ion movements are disrupted

Vibrio cholerae bind to intestinal epithelial cells releasing their enterotoxins; the toxin binds to sugar groups on the membrane Binding of enterotoxin Vibrio cholerae Cholera toxin activates an enzyme that catalyses the conversion of ATP to cyclic AMP (cAMP) within the cells Adenyl cyclase cAMP Cholera toxin ATP Increased cAMP levels block the transport of Na+ into the epithelial cells and bring about the active secretion of chloride ions into the lumen X Na+ Cl- Explain how the action of the enterotoxin leads to copious, watery diarrhoea

Vibrio cholerae bind to intestinal epithelial cells releasing their enterotoxins; the toxin binds to sugar groups on the membrane Binding of enterotoxin Vibrio cholerae Cholera toxin activates an enzyme that catalyses the conversion of ATP to cyclic AMP (cAMP) within the cells Adenyl cyclase cAMP Cholera toxin ATP Increased cAMP levels block the transport of Na+ into the epithelial cells and bring about the active secretion of chloride ions into the lumen X Na+ Cl- The change in ion concentrations across the epithelial cells disrupts the osmotic balance; the large concentration of ions in the intestinal lumen leads to the osmotic movement of large amounts of water into the lumen H2O

Cholera-induced dehydration is rapid and can quickly lead to death; this patient is being given oral rehydration therapy (a solution of glucose and salts) to counteract the severe dehydration

During a Cholera epidemic in Peru, some of the very ill patients are being treated by intravenous drip to counteract their severe dehydration

Prevention of Cholera The principle issues that need to be addressed to prevent outbreaks of cholera are: Improvements in water supply Improvements in sanitation and sewage disposal Food safety Community awareness of preventative measures Political commitment Oral cholera vaccines have recently become available for use by individuals; the use of vaccines as a preventative measure is still being researched and reviewed Use a variety of resources to research the current status of oral cholera vaccines

World Health Organisation – July 2004 “Cholera remains a global threat and one of the key indicators of social development. While the disease no longer poses a threat to countries with minimum standards of hygiene, it remains a challenge to countries where access to safe drinking-water and adequate sanitation cannot be guaranteed for all. Almost every developing country is facing either a cholera outbreak or the threat of a cholera epidemic.” World Health Organisation – July 2004