G is Giardia
Giardia is a protozoal infection (giardiasis) that infects the intestines of mammals, birds, and amphibians. It is most commonly contracted and spread through fecal oral contamination – inadequate hygiene and eating or drinking contaminated food and water.
Symptoms are related to the gastrointestinal tract – diarrhea, gas, and dehydration. Dehydration can be so severe that hospitalization may required. Diagnosis is through fecal testing – looking for the parasite under the microscope or other laboratory tests. In animals, an in office snap test can be used and generally only takes about 8-10 minutes.
Treatment generally focuses on antibiotics, cleaning of the environment as it can survive for long periods of time outside of the body, and supportive care, such as fluid therapy.
Although there are many types of giardia, there is a small risk of cross species infection of giardia from dogs and cats to people. The CDC has a lovely page on pets and giardia.