Giardia duodenalis (G. lamblia and G. intestinalis) are flagellated, single-cell protozoan that cause Giardia infections. Giardiasis is the most common parasitic intestinal infection in the US. Infection occurs when people come into contact with Giardia, usually via contaminated water. Giardia can form an outer shell, called a cyst, allowing it to survive outside of a body for long periods of time. Because of the cyst, Giardia is able to survive in natural bodies of water like lakes and streams and is less likely to be affected by chlorine and other municipal water treatments. Not only can it survive in natural bodies of water, it can also survive in swimming pools and tap water. Even if the water looks clean, Giardia can still be present in it. Make sure to filter any water consumed in nature.
To test for Giardia a stool sample is required. The symptoms of Giardiasis include abdominal cramps, gas, belching, and watery, foul-smelling diarrhea. Nausea is also a symptom but it may persist or subside throughout the infection. Tiredness, general malaise, and lack of appetite are also symptoms of Giardiasis. Diarrhea may last for weeks if the infection is not treated, and people who have had Giardiasis may become lactose intolerant. In severe cases the diarrhea can last even longer and may result in malabsorption of nutrients, leading to significant weight loss. Typically it takes one to two weeks after infection for symptoms to appear. The current treatments are delayed if possible if the person suffering the infection is pregnant. If the symptoms are severe, a specific treatment may be used, but it is only used in this instance. Even after being cured, lactose intolerance or irritable bowel syndrome may persist.