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Giardiasis is an intestinal infection caused by a protozoan organism called Giardia intestinalis. It is a water-borne parasite, which means it survives in lakes, streams, ponds, puddles, wet grass and damp soil. Many healthy adult pets with no diarrhea will have small numbers of Giardia in their intestinal tracts. We generally only test and treat for it in adult pets if the dog or cat has signs of illness. Because of their immature immune systems, Giardia is more likely to cause serious illness in young pets. When we find Giardia in a puppy or kitten we will treat for it even if the pet doesn’t currently have diarrhea.

Infection is very common in puppies and kittens, affecting about 1/3rd of them. It is especially common, too, in kennels and breeding facilities, because the organisms survive a long time in damp concrete runs or yards. A pet becomes infected with Giardia by swallowing the cyst stage of the parasite. Licking or smelling the stools of other pets or drinking contaminated water easily spreads them. The cyst goes through several stages of maturation in the intestines before it can reproduce. It will then be shed in the stool and be infective to other pets.

Many pets do not seem to be bothered by the Giardia in their intestines, but others become ill. The immune system can cope with a small number of these parasites but in large numbers or with stress on the immune system or gastrointestinal system symptoms may develop. Examples of triggers would be staying in a kennel, changing pet foods, or having another parasite or infection. Elderly or debilitated animals and young puppies and kittens are the most likely to show symptoms.

Symptoms include vomiting, diarrhea, belching and flatulence. There may be blood or mucous in the stool. Signs may be acute (come on suddenly) or the pet may have milder but persistent symptoms such as on and off diarrhea or occasional nausea. Giardia symptoms often wax and wane, flaring up repeatedly. If a pet has recurrent infection with Giardia we start looking for an underlying cause, such as food allergy or inflammatory bowel disease. A normal pet with a healthy intestinal tract should not be having recurrent diarrhea from Giardia.

During flare-ups pets are especially contagious to other animals, which is a concern when pets are boarding or going to the dog park. Keep your dog home if it has diarrhea and be careful to pick up as much stool as you can from your yard, to decrease the chances of reinfec-tion later on.

Sometimes Giardia may be seen on a routine fecal flotation test looking for intestinal parasites. We are finding Giardia more frequently on routine fecal testing since we and our outside laboratory use a centrifuge for fecal testing. This is a better method of testing than what most veterinary hospitals currently do. More often, though, infection may be missed, as Giardia are passed only intermittently in the stools and they die quickly outside the body unless kept moist. If we suspect a pet may have it, we rely on a special Giardia antigen stool test that is specific for Giardia and is 95% accurate. We run this test, in addition to the regular parasite check, on all puppies and kittens, and on many pets with diarrhea.

Metronidazole (Flagyl) used to be commonly used to treat for Giardia but sometimes, depending on the strain of Giardia, the parasites are resistant to this antibiotic. Benzimidazole dewormers such as Panacur are more effective and commonly used, though we are seeing more and more Giardia infections resistant to Panacur, too – about one in five Giardia infections won’t clear completely with Panacur alone. Some patients need both metronidazole and Panacur together to cure the symptoms. If there are multiple pets in the household, testing or treatment may be recommended for all of them. Repeat testing is needed to ensure that the infection clears and that the pet is not being reinfected from its environment.

The environment may need to be treated to prevent reinfection. One cup of chlorine bleach in a gallon of water is an effective disinfectant for Giardia cysts. If your dog has a kennel or an outdoor concrete or gravel run you should disinfect it, and cat litter pans should also be treated with bleach solution. Be sure to let the bleach sit for a few minutes to completely kill the Giardia cysts. Bleach is caustic and can be harmful to pets so rinse thoroughly after using it.

Giardia cysts can cling to a pet’s fur and reinfect the pet when it licks itself. Bathing the dog or cat during the Giardia treatment period will decrease the risk of reinfection. Probiotics such as FortiFlora improve the effectiveness of metronidazole and Panacur so we usually recommend you give a probiotic along with medication. Extra fiber in the diet may help with recurrent cases.

Giardiasis is the most common intestinal parasite of man, as well as being common in pets. However, current research suggests that most people do not acquire the parasite from their pet, as people and pets tend to have different strains of the disease. In some cities without adequate water treatment, Giardia may be acquired from drinking water. Never the less, take precautions if your pet has been diagnosed with Giardiasis - wash your hands, keep the yard free of stools and clean litter boxes often, using bleach and then rinsing well. Small children, the elderly, and people with AIDS or other immune system-compromising diseases should use extreme care.


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