What is Giardia?
Giardia is a microscopic, single-celled, parasitic organism that causes an intestinal infection in humans and animals called giardiasis. The Giardia parasite occurs worldwide and is a common cause of "Traveler's Diarrhea" in humans. Outdoor enthusiasts who drink contaminated water may develop "beaver fever," another name for giardiasis in humans.
Giardiasis can be an important cause of diarrhea in animals and people. However, most 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 (trophozoite) lives in the gut of infected animals. A hardy cystic form is shed in feces and can survive several months in the environment, particularly in water and damp environments.
How are dogs infected with Giardia?
A dog becomes infected with Giardia when it swallows the cyst stage of the parasite. When the cyst passes into the dog's intestines, it transforms into the trophozoite form and attaches to the intestinal wall to feed. If there are enough trophozoites, the dog will develop clinical signs of damage to the intestinal wall.
Trophozoites reproduce by dividing, and some transform into the cystic form. Eventually, the dog passes infectious cysts in its stool. The time from ingestion of cysts to passage in feces is 5 to 12 days in dogs. These cysts can immediately infect another animal. Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground or drinking contaminated water.
When Giardia cysts are found in the stool of a healthy adult dog without diarrhea, they are generally considered a transient, insignificant finding. However, in puppies and debilitated adult dogs, they may cause severe, watery diarrhea that may be fatal if left untreated.
Dogs are more likely to develop disease when large numbers of cysts are present in the environment due to fecal contamination. Giardiasis is common in densely populated environments, such as kennels, pet stores, or animal shelters.
What are the clinical signs of giardiasis?
Clinical signs include:
- Acute, sudden onset of foul-smelling diarrhea
- Weight loss
- Chronic, intermittent diarrhea, ranging from soft to watery
- Fatty stool
- Stool with a greenish tinge
- Blood in the stool
- Excess mucus in the stool
- Vomiting
- Low energy
Signs may persist for several weeks, and gradual weight loss may become apparent. Younger animals are more likely to exhibit clinical signs. The disease is not usually life-threatening unless the dog’s immune system is immature or compromised. Many dogs are asymptomatic carriers and never develop any signs of illness.
How is giardiasis diagnosed?
A routine fecal flotation test may fail to detect tiny Giardia cysts, which are shed inconsistently in the feces and often require a special zinc sulfate flotation solution. Occasionally, the parasites may be seen on a direct smear of the feces.
If your veterinarian suspects giardiasis, they may request a stool sample to be analyzed for Giardia-specific antigens (cell proteins). Some Giardia tests are available for in-clinic use, while others must be submitted to a reference laboratory. Many cases are presumptively diagnosed based on medical history and clinical signs.
How is giardiasis treated?
The most common drugs used to kill Giardia are fenbendazole (Panacur®) and metronidazole. These drugs are usually given for 3 to 10 days. These drugs may be given together, if necessary. This combination is usually administered to dogs with refractory diarrhea (diarrhea that has not responded to treatment). Your dog may need supportive treatment with other drugs if dehydration or severe diarrhea is present.
A low-residue, highly digestible diet may help lessen loose stools during treatment and some pets may benefit from added fiber. Probiotics may also be recommended. Some dogs may require follow-up tests and treatments based on their condition and severity of infection. Your veterinarian will help determine the best treatment for your pet.
Giardia cysts are infective as soon as the dog passes them, so you must quickly remove feces from the environment and dispose of them. Bathe infected animals regularly to remove cysts from their hair coat.
What is the prognosis for giardiasis?
The prognosis is good in most cases. Debilitated or geriatric animals and those with incompetent immune systems are at increased risk of complications, including death. All pets diagnosed with Giardia should be re-tested two to four weeks after they complete treatment.
Can my dog give Giardia to me or my family?
Giardia can cause diarrhea in humans and can be passed from dogs to humans. In the past, it was assumed that cats, dogs, and wildlife were an important source of human infection. Although there is some controversy as to how easily infection passes between dogs and humans, it is best to assume that it could occur. Human-to-human transmission is also important, such as contaminated municipal water supplies.
If your dog is diagnosed with giardiasis, it is essential to disinfect the environment and maintain good personal hygiene to prevent accidental spread to humans. People undergoing chemotherapy or those with immunodeficiency, such as AIDS or cancer, should use extreme care, especially when handling feces or administering medications.
For environmental disinfection, you can use chlorine bleach at 1:32 or 1:16 dilution, or 1 to 2 cups of bleach in a gallon of water (60-120 mL of bleach per liter of water). However, be sure that the affected surfaces can be safely treated with bleach.
Lysol® and quaternary ammonium compounds (e.g., Parvosol®) are also reported to kill cysts effectively. Giardia cysts are susceptible to drying, so keep your environment as dry as possible. For best results, thoroughly clean the pet's living and sleeping areas and then allow the areas to dry out for several days before reintroducing pets.
