Diarrhea. Nobody wants it, but everyone gets it, including dogs and cats. The culprit most commonly blamed for it is diet–"something he ate." However, that's not always the case. In animals it's just as common to see diarrhea or loose stools from parasites.

One parasite in particular is becoming more and more a problem in animals and in man. That parasite is a protozoa, or a one celled organism called Giardia.

Animals and man alike contract Giardiasis (an infection in the small intestine caused by Giardia) by eating or drinking substances contaminated with Giardia cysts. The cysts are the inactive and infective form of the protozoa that survive in the environment. Able to withstand a tremendous range in temperature and humidity, they've been found in high mountain streams in the Rockies and in the deserts of the Southwestern United States.

When an animal swallows a Giardia cyst, the gastric acid in the stomach ruptures it and allows the parasite to infect the small intestine. It takes approximately eight to ten days for the animal to begin to feel ill. The sign normally seen with a Giardia infection is diarrhea, which tends to be thick and greasy instead of bloody and watery. It can lead to life-threatening complications such as dehydration and weight loss. This is especially dangerous in very small puppies and kittens. It doesn't take much dehydration or weight loss to kill a very young dog or cat.

Giardiasis is not easily diagnosed by veterinarians; it's a very difficult organism to see under the microscope. When Giardia is suspected, a stool sample is taken and placed on a microscope slide along with a special stain. If Giardia is found, it's diagnosed as the causative agent of the diarrhea. If it's not found, yet another test is usually performed to completely rule it out.

The second test is a laboratory test that also examines a small amount of feces from the animal. It's 98 percent accurate. Veterinarians primarily use the microscope test first because the laboratory test is more expensive and is unnecessary if a positive test can be made under the microscope.

The only good thing about Giardia is that it's relatively easy to cure. Usually, a five to seven day dose of the antibiotic Metronidazole will rid the animal of the infection. On rare occasions, the animal can become chronically infected with the protozoa, and more extensive treatment is required. The very young and the very old are the most susceptible to the disease, and an animal can catch Giardia more than once.

A new vaccine for dogs has been developed to fight against Giardia. It has proven to be quite effective in controlling the disease, especially in areas where Giardia may become a chronic problem, such as in kennels or grooming facilities. Owners of dogs who have recurring infections should consult their veterinarians about using the vaccine.

One very important consideration to remember is that Giardia is a disease that people can catch from their pets. Owners of a dog or a cat that's diagnosed with Giardia must be sure to wash their hands after handling their animals. Also, any surface soiled with feces should be washed with a bleach water solution.

No one wants their pet to have diarrhea. Fortunately, veterinarians have the tools to diagnose, treat and prevent it.

Jeff Henderson is a partner and veterinarian at Britton Road Veterinary Clinic in Oklahoma City. After getting his B.B.A. from OU, he developed real estate for eight years before going to OSU for his D.V.M. Jeff, his wife and daughter have a boxer and a cat. Though his practice consists of treating mainly dogs and cats, Jeff has special interest in the care of exotic animals.

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