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 humans. However, many cats infected with Giardia do not have diarrhea, vomiting, or any other signs of illness. Giardia infection in cats is undoubtedly more common than recognized or diagnosed.
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 cats infected with Giardia?
A cat becomes infected with Giardia when it swallows the cyst stage of the parasite. When the cyst passes into the cat'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 cat passes infectious cysts in its stool. The time from ingestion of cysts to passage in feces is 5 to 16 days in cats. These cysts can immediately infect another animal. Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground or drinking contaminated water.
Giardiasis is relatively rare in healthy adult cats. Cats are more likely to develop disease when large numbers of cysts are present in the environment due to fecal contamination. It is more common in kittens and debilitated adult cats and often occurs in densely populated groups of cats, such as catteries, 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. The disease is not usually life-threatening but can be more severe in kittens, older cats, and cats with an immune system damaged by Feline Immunodeficiency Virus (FIV), Feline Leukemia Virus (FeLV), or other serious illnesses. Many cats are asymptomatic carriers and never develop signs of illness. Younger animals are more likely to exhibit clinical signs.
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 diagnosed based on medical history and clinical signs.
What is the treatment for giardiasis?
The most common drugs used to kill Giardia are Fenbendazole (Panacur®) and metronidazole. These drugs are usually given orally for 5 to 7 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 cat may need supportive treatment with other drugs if dehydration or severe diarrhea is present.
These drugs can be very bitter, so they are often manufactured in a coated tablet form. To get the correct dose for cats, the tablet must often be split, thus exposing the bitter contents. To make it easier to administer these medications, veterinary compounding pharmacies can prepare them in flavored formulas that mask the bitterness. 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 cat 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 cat give Giardia to me or my family?
Giardia can cause diarrhea in humans and can be passed from cats to humans. In the past, it was assumed that cats, dogs, and wildlife were important sources of human infection. Although there is some controversy as to how easily infection passes between cats 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 cat 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.
