Goals of Treating Giardia
Giardia is treatable, usually on an outpatient basis. Unfortunately, the effectiveness of treatment is evaluated based on the presence or absence of cysts in the affected dog’s feces, which does not necessarily equate with whether the parasites are present inside of the dog. A dog can remain internally infected, without shedding the cyst form of the organism at the time the fecal sample is taken. In addition, infection can recur after the parasite is initially eliminated from a dog’s gastrointestinal tract. In other words, the first infection does not provide any immunity or protection against later infections.
The goals of treating giardiasis are to eliminate the shedding of infective cysts, eliminate the symptoms of the illness (diarrhea, abdominal pain, weight loss, etc.), and return the dog to a comfortable, pain-free quality of life.
The antibiotic drug metronidazole (Flagyl), and the anti-parasitic drug fenbendazole, are among the most frequently-used treatments for giardiasis in dogs. Other de-worming medications are available as well, includeing combinations of febantel, praziquantel and pyrantel pamoate, among others. While these drugs treat the parasitic infection, they also can cause of harmful side effects, such as liver damage. Many veterinarians will not prescribe metronidazole or fenbendazole unless the dog is showing moderate to severe symptoms of giardiasis. Metronidazole can cause physical malformations in developing embryos, so it should not be given to pregnant bitches. The same is true for a related medication, albendazole. Metronidazole also reportedly has a very bitter taste, making it difficult for some owners to administer. Some of these drugs reportedly also can cause acute anorexia, depression and vomiting.
Even with treatment, it is possible that only the cystic form of Giardia has been removed from the feces, while the infective trophozoite form in the dog’s small intestine remains. In other words, fecal tests for Giardia can be negative, but the parasites still can live inside the dog’s gastrointestinal tract, making those dogs a source of potential infection for other animals, and possibly for people. Giardia is rarely deadly in otherwise healthy dogs. Dogs infected with this parasite typically have flu-like symptoms that eventually resolve.