Giardia:  Single-celled parasite.

Common in:  Dogs living in kennel type situations (shelters, pet stores, etc.) 

Can be found in: Intestines of dogs, cats, and humans.

Diagnosis: Microscopic fecal exam from very fresh fecal specimen.  Note: False negative tests are common, so treatment without verification is common.

Treatment: Oral medication.

Possible Symptoms: Intermittent or continuous diarrhea, weight loss, depression, and a loss of appetite.

Possible Transmission: Infected feces contaminating the yard.  

Lifestyle Prevention: Careful disposal of all fecal material; cleaning contaminated areas.  

Medical Prevention: Vaccination.  Note:  Effectiveness of the vaccination is questionable at this time.  

Zoonotic Transmission: Yes; wash hands and utensils.