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Giardia Infection in Cats




Overview
Predisposition
Clinical Signs
Causes
Diagnosis
Treatment
Prognosis
Prevention
Transmission to Humans

Overview

Giardiasis is an intestinal infection of man and animals 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 prevalence rate is high in cats and dogs, clinical disease is less common.

Predisposition

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. The number of cysts shed in the feces of infected cats fluctuates with time, and may vary from animal to animal. Also, kittens have been shown to shed more Giardia cysts in their feces than older cats.

Similarly, human infection is more common in dense populations. Scientific studies have demonstrated greater prevalence in nursing homes and day-care centers when compared to the population at-large. Giardia is the most common intestinal parasite in humans in North America.

Clinical Signs

These microscopic parasites attach themselves to the intestinal wall (particularly the upper portion of the small intestine) and cause a foul-smelling diarrhea. The stool may range from soft to watery and occasionally contains blood. Infected cats tend to have excess mucous in the feces. Sometimes, vomiting can occur.

A sudden onset of diarrhea is the most common scenario, but Giardia may also be associated with chronic diarrhea. Severe disease may occur in young animals, kittens or puppies with other GI parasites, or debilitated animals. It may sometimes also occur in healthy patients. Some of the difference in pathogencity (severity of illness) may be associated with parasite strain variation.

Causes

Ingestion (swallowing) 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 that has been contaminated with the cysts.

Diagnosis

Because of the prevalence of Giardia in the cat, 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 higher risk for dehydration associated with the 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 to increase the likelihood of accurate identification of the cysts in the stool. Occasionally, the parasites may be seen on a direct smear of the feces. An in-hospital test is also now available for detection of antigens (cell proteins) of Giardia in the feces. This test is more sensitive and more specific versus the routine "fecal analysis," and is run on those cats in whom Giardia infection is thought to be a likely possibility.

Treatment

Metronidazole and Fenbendazole are the drugs most commonly used to treat Giardia. Other treatments may be needed as supplemental therapy. Treatment may eliminate shedding, but will not necessarily eliminate infection.

Prognosis

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

Prevention

The best prevention for development of Giardiasis is to avoid drinking contaminated water, and to monitor cats closely who are in high density living arrangements (catteries, shelters, etc.), especially where cats with unknown histories are being introduced. There is a Giardia vaccine available now. However, the vaccine is adjuvanted (i.e., it has added components to enhance the patient's immune response to the vaccine). Adjuvanted vaccines are more likely to be associated with local vaccine reactions. Additionally, although the vaccine may help to decrease the shedding level in an endemic Giardia environment, it does not prevent infection. For these reasons the Giardia vaccine, when used at all, is used more in shelter or cattery cats than in "owned" cats.

Transmission to Humans

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 the more important factor. Also, in cities that do not have water treatment facilities with a sand filtration system, Giardia may not be removed from drinking water. There is currently no conclusive evidence indicating that cysts shed by dogs and cats are infective for humans.

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. First be sure that the surfaces and premises can be safely treated with bleach.



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