Smallpox, typhoid fever, bubonic plague, cholera... These may be health problems you know best from history class—or even from novels in your literature class. In a world in which super-bugs lurk on the medical fringe and new viruses like H1N1 and SARS have threatened to explode to pandemic proportions, it's sometimes easy to discount diseases, viruses, and bacteria that have proven epidemic in the past.

But many of these bugs from "long ago" haven't ever completely disappeared. A bit of research on health crises through the years shows a number of repeat offenders, outbreaks that have returned on an epidemic scale, time and again and around the world.

For example, high incidence of Cholera showed up in 2007 and 2008 in Vietnam, and in both India and Iraq in 2007. In recent months, cholera has reared its head in mass numbers, sweeping through both Haiti and Nigeria.

Can You Catch It?

An infection that attacks the small intestine, cholera is caused by the bacterium Vibrio cholera. Luckily, cholera is not an airborne disease—unless picked up and spread by a natural disaster like a tornado or hurricane. The disease is transmitted primarily through contaminated water or food, and in impoverished conditions, poor sanitary conditions and inferior (or nonexistent) sewage removal systems contribute to the spread and risk.

What's in the Water?

Water is an essential staple for life. But the water we drink and use day to day has to be safe. If it isn't purified, water may contain compounds we don't want to drink (like salt or toxic elements like lead), or it may contain pathogens, like the bacteria that causes cholera.

To learn more about testing and purifying water, check the following Science Buddies project ideas:

• Solar-Powered Water Desalination (Difficulty: 6-7)
• Learn How to Disinfect Contaminated Water (Difficulty: 7-9)