Being aware of and educating our clients about potential zoonotic diseases is an important part of what we do at the Animal Clinic at Thorndale. Giardia is a parasite that is shared across many species, including cats and humans.
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 a important cause of illness in animals and man. Fortunately, even though the prevalence rate is high for Giardia in cats and dogs, clinical disease is less common.
Predisposition
Infection is relatively rare in healthy pets. It is more common in densely-populated groups of animals, such as in a kennel, cattery, pet store, or animal shelter. Also, puppies and kittens have been shown to shed more Giardia cysts in their feces than older dogs and 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.
Clinical Signs
These microscopic parasites attach themselves to the intestinal wall and cause a sudden-onset (acute) 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.
Causes
Ingestion (swallowing) of the cyst stage of the parasite leads to infection. Once inside the pet’s intestine, the cyst goes through several stages of maturation. Eventually, the pet is able to pass infective cysts in the stool, where they can contaminate the environment and infect other animals.
Infection can also occur from drinking water that has been contaminated with the cysts.
Diagnosis
Because of the prevalence of Giardia in pets, presence of cysts in the stool does not necessarily indicate that illness or diarrhea is present. However, when the cysts are present in a pet with diarrhea, it is important. In particular, puppies, kittens and debilitated adult dogs and cats are at risk for death from dehydration associated with the diarrhea. Keep in mind that the cysts in the stool are potentially infectious to humans.
Although a fecal examination is needed for diagnosis, the routine flotation test may fail to detect these small cysts. A special solution is needed for accurate identification of the cysts in the stool. Most laboratories can have the test result within a day. 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 this particular test is only performed in select laboratories.
Treatment
Metronidazole and fenbendazole are the drugs most commonly used to treat Giardia. The former is a tablet, and the latter is a powder stirred into the food. They are given orally for 5-7 days. Other drugs may be needed as supplemental therapy should diarrhea and dehydration occur.
Prognosis
The prognosis is good in most cases. Debilitated or geriatric animals and those with incompetent immune systems are at increased risk for death.
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, some research indicates 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 which do not have water treatment facilities with a sand filtration system, Giardia may not be removed from drinking water.
Nevertheless, until the issue of transmission is resolved, caution is advisable when a pet has been diagnosed with giardiasis. Good hygiene, especially hand washing after handling pets, is important. 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.