Giardiasis (pronounced "jee-ar-DYE-uh-sus"), or giardia, is an infection of the intestines caused by the parasite Giardia lamblia. You may become infected with giardia if you eat food or drink water that is contaminated with human or animal waste. You can also get giardia by coming into close contact with an infected person. The illness is most often a problem in developing countries where tap water is not safe; but you can get giardiasis in developed countries, too. In the UK, water purification systems mean that it is very unlikely that tap water could be contaminated by Giardia. However, avoid drinking untreated water from rivers, or lakes. This is true even in mountain lakes and streams, where the water may seem pure. Follow the links below to find BootsWebMD's comprehensive coverage about how giardiasis is contracted, what symptoms it causes, how to treat it and much more.