Since the cysts are excreted only from time to time and trophozoites even less often, analyzing just one or two fecal samples may miss them. Parasitologists recommend repeated stool examinations or analysis of a sample of the intestinal contents. The trophozoites or cysts can sometimes be seen under a microscope, but immunological tests that detect proteins from the parasite are most effective for making an accurate diagnosis. But veterinarians commonly use a far less accurate test. Veterinary experts say that unless the stool sample is floated in a zinc sulfate solution and then strained and centrifuged, it is very easy to miss the giardia parasite.
Treatment is another problem.
There is none known that is 100 percent effective, and all the drugs that kill giardia have nasty side effects. Less common but more serious side effects include seizures and numbness and tingling in the arms, legs, hands and feet. Further complicating treatment is that some giardia organisms have developed resistance to Flagyl. For treatment of a pet and pet owners to have a lasting effect, it is crucial to prevent reinfection. First, if a pet has been given a diagnosis of giardiasis, those in close contact with the animal, and especially any children in the household, might also be tested.