Giardiasis is an intestinal infection of man and animals. It is caused by a protozoal parasite called Giardia intestinalis. It is widely known as the source of ‘traveler’s diarrhea.” These single-celled parasites are not to be confused with the common intestinal parasites: roundworms, hookworms, and tapeworms.

Giardiasis is an important cause of illness in animals and man. Fortunately, even though the infection rate is high in cats and dogs, clinical disease is less common.

Which cats are likely to get giardiasis?

Infection is relatively rare in healthy cats. It is more common in densely-populated groups of animals, such as in a cattery, pet store, or animal shelter. Also, kittens have been shown to shed more Giardia cysts in their feces than older cats.

What are the clinical signs?

These microscopic parasites attach themselves to the intestinal wall and cause an acute (sudden-onset) foul-smelling diarrhea. The stool may range from soft to watery and occasionally contains blood. Infected cats tend to have excess mucus in the feces. Sometimes, vomiting can occur.

How do cats get infected with giardia?

Ingestion of the cyst stage of the parasite leads to infection. Once inside the cat's intestine, the cyst goes through several stages of maturation. Eventually, the cat is able to pass infective cysts in the stool, where they can contaminate the environment and infect other cats.

Infection can also occur from drinking water which has been contaminated with the cysts.

How is the diagnosis made?

Because of the prevalence of Giardia in the cat, the presence of cysts in the stool does not necessarily indicate that a problem is present. However, when the cysts are present in a cat with diarrhea, it is important. In particular, kittens and debilitated adult cats are at risk for death from dehydration associated with diarrhea.

Although a fecal examination is needed for diagnosis, the routine flotation test may fail to detect these small cysts. A special solution may be needed for accurate identification of the cysts in the stool. Occasionally, the parasites may be seen on a direct smear of the feces. A test is available for detection of antigens (cell proteins) of Giardia in the feces. A delay of several days may occur as the test is only performed in select laboratories. Also, the reliability of this test in the cat remains under investigation.

What is the treatment?

Metronidazole is the drug most commonly used to treat Giardia. It is a tablet which is given orally for 5-7 days. Other drugs may be needed as supplemental therapy should diarrhea and dehydration occur.

Another antiparasitic drug, fenbendazole, is being investigated as a potentially useful treatment. It appears to be very effective and may be used in cats with refractory diarrhea as a means of diagnosing and treating Giardia.

What is the prognosis?

The prognosis is good in most cases. Debilitated or geriatric animals and those with incompetent immune systems are at increased risk for death.

Can Giardia affect me or my family?

Giardiasis is the most common intestinal parasitic infection of man. In the past, it has been assumed that cats and dogs served as the source of infection for humans. However, current research is beginning to indicate that perhaps cats and dogs do not serve as an important reservoir of the disease for man. Some scientists are suggesting that human-to-human transmission may be a more important factor. Also, in cities which do not have water treatment facilities with a sand filtration system, Giardia may not be removed from the drinking water.

Nevertheless, until the issue of transmission is resolved, caution is advisable when a pet has been diagnosed with giardiasis. In particular, humans with immunodeficient states (AIDS, chemotherapy) should use extreme care.

For environmental disinfection, a cup of chlorine bleach in a gallon of water is effective. However, be sure that the surfaces and premises can be safely treated with bleach.

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