THE CHOLERA STORY
Cholera is a killer disease, especially of children in developing countries. When people drink water contaminated by Vibrio Cholera, they suffer drastic fluid loss (dehydration) through diarrhea. Sick people can lose 2-3 gallons a day.
Symptoms show up quickly in children. Children are at a much higher risk of fluid loss because they exchange about a 1/5th their body fluids normally every day, a turnover amount much higher than that of adults (1/7th). Children will quickly show secondary symptoms of life-threatening dehydration, including thirst, sunken eyes, dry tongue, shriveled fingertips, and weakness. If untreated, especially in young children, loss of consciousness and death can follow rapidly.
Other dehydrating diseases include Rotavirus, Shigella, and Typhoid Fever. The way people get any of these diseases, including Cholera, is usually by eating or drinking something contaminated with a parasite, virus, bacteria or other infectious microbe.* The disease organisms grow quickly in the digestive tract, disrupting the normal functions the tract is designed to perform.
Cholera works by attacking cell membranes, changing the balance of water and dissolved particles inside and outside the cell. Investigators found that when someone has the disease cholera, the cholera bacteria, Vibrio Cholera, sticks to the walls of the intestines and makes many tiny holes, or pores, through the cell membranes of the cells of the intestinal walls.* Since all cells have water, the cells lost water through its pores.
For a long time people tried simply to replace the lost fluids of these patients with water. But that didn't work. Why not? What else is in a cellular fluid besides water? Why would that be important?
Water in body tissues normally also transports energy nutrients like sugar, together with critical salt ions like sodium and chloride, useful for cell signals, into our cells. Water also carries out cell wastes. Keeping the right amount of water in the cells, and keeping the materials like salt and sugar in stable solutions, is therefore critically important. (Atheletes, too, who sweat a great deal, need to be very careful to maintain the right amount of water, salt and sugar. They often drink special drinks in order to stay hydrated and strong. Which drinks may be the healthiest for atheletes? Is there salt lost in sweat?)
A normal cell regulates the amount water and nutrients by a series of openings, called pores, set within its outer membrane. The shape and size of many pores are designed to allow just one or two kinds of molecules through. Water, for example, passes through its own "aquapores." Some openings, on the other hand, are not so specific, and let many different types of molecules through. The holes made by the cholera bacteria allow water, sugar and salts to leave the cell.**
Consequently, the water and salt loss effects the shape of a cell, decreasing a cell's roundness (turgor). The cell becomes very wrinkled. As our cells are also designed to be a certain shape, fitting and working together in a tissue, a change in shape can effect the way the cell and the tissue work.
Discovering how best to restore the salt, sugar and water balance has been an important medical success, saving many lives. (Curious? Go on to read The Oral Rehydration Story) Now, when Cholera breaks out, tents are immediately put up and intravenous solutions containing just the right amount of salts and sugars to repair the cells and save lives are are rushed to the area.
You can learn more about cholera
Summary in Science, vol. 292, 6 April 2001, from Cell, 104, 937 (2001)
Research on the web: key words -- cholera, vibrio cholerae, oral rehydration
Learn about another membrane-attacking diseases:
Cystic Fibrosis is in many ways the opposite condition of Cholera. Salt is retained, water moving to accompany the salt across the membrane gradient, and the outside muscus layer is thickened, making it hard to breathe and operate in general.
_______________________ *After the bacteria cholera protein attaches to a cell surface; a portion breaks off and enters cell to interfere with the energy production at the cell membrane, energy that is needed to maintain pores. The pores in the membranes, therefore, don't work well, and water rushes out of the cell.
**This system of membranes with pores developed because cells in the early soupy water of Earth's history did better if they concentrated nutrients such as sugars and salts, as well as proteins and other useful materials, closely together inside cell. Cells tend to want more of some molecules, for example, and less of others. Putting the ingredients closely together in the cell made a kind of reaction chamber in which life processes could be encouraged to "go". The membrane developed openings designed not only to let certain molecules enter and exit, but also to regulate which direction they should go.
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