What is Giardia?
Giardiasis is an intestinal infection that can be transmitted to humans and animals. It is a one-celled parasitic species; it is not a “worm”, bacteria or virus.
Giardiasis can be an important cause of illness, especially diarrhea, in animals. However, the majority of dogs infected with Giardia do not have diarrhea, vomiting, or any other signs of illness. The Giardia organism has two forms. A fragile feeding form, known as the trophozoite, exists in the gut of infected animals, while a hardy cystic form is shed in feces and can survive several months in the environment, particularly in water and damp environments.
How do dogs get giardiasis?
A dog becomes infected with Giardia when it swallows the cyst stage of the parasite. In susceptible dogs, once the cyst passes into the dog’s intestines, it goes through a transformation to the trophozoite, or feeding form, and attaches to the intestinal wall to feed. If sufficient numbers are present, clinical signs of damage to the intestinal wall will develop. Eventually, the dog passes infectious cysts in its stool. The time it takes from ingestion of cysts to passage in feces is 5 to 12 days in dogs and 5 to 16 days in cats. These cysts are immediately able to infect another animal. Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground, or by drinking contaminated water.
What are the clinical signs of giardiasis?
These microscopic parasites attach themselves to the intestinal wall and the damage causes an acute, sudden-onset of foul- smelling diarrhea. Infection in dogs may lead to weight loss, chronic intermittent diarrhea, and fatty stool. The stool may range from soft to watery, often has a greenish tinge to it, and occasionally contains blood. Infected dogs tend to have excess mucus in the feces. Vomiting may occur in some cases. The signs may persist for several weeks and gradual weight loss may become apparent.
How is giardiasis diagnosed?
A routine fecal flotation test may fail to detect these tiny cysts, which are shed inconsistently in the feces, and which often require a special zinc sulfate flotation solution for detection. Occasionally, the parasites may be seen on a direct smear of the feces. If your veterinarian suspects giardiasis, a sample of stool may be analyzed for the presence of specific antigens (cell proteins). Some tests are available for in-clinic use while other tests require you to submit a stool sample to a reference laboratory.
How is giardiasis treated?
The most common drugs used to kill Giardia are fenbendazole and metronidazole. These drugs are normally given for three to ten days. Both drugs may be given in combination if necessary. This combination is usually administered to dogs with refractory diarrhea (diarrhea that hasn’t responded to treatment). Supportive treatment with other drugs may be needed as supplemental therapy if dehydration or severe diarrhea is present. Your veterinarian will help determine what course of treatment is best for your pet.
Because Giardia cysts are infective immediately when passed into the environment, feces should be removed quickly and disposed of. Infected animals should be bathed regularly to remove cysts from the hair coat.