Guard Against Giardia

By: Audi Donamor
As seen in: AWM Vol. 16 Issue 3

Lakes, streams and ponds can host this troublesome parasite. If you’re taking your dog on vacation near water this summer, help protect him by keeping his GI system healthy.

We once took our dog on a road trip in Northern Ontario. We stayed at a beautiful lakeside resort that offered the perfect playground for him. Each time he went in the water, he took great delight in drinking from the lake when he wasn’t swimming and playing. While he ate his meals with gusto, he threw up afterwards, and had loose stools as well. There was no lethargy, no temperature, nothing that would indicate anything was wrong, but I called our veterinarian back home for advice.

We decided to wait and see what the next day would bring. After another day of swimming, water play, and drinking from the lake, our dog again threw up his dinner and had diarrhea a half hour after eating.

After two days of this, we packed up and headed home. There was no more vomiting or loose stools, but being the Triple “A” personality that I am, I got our vet to run some tests.

“It could be giardia,” the veterinarian said. “It could have been introduced into your dog’s system during his adventures in the lake.” We never found out for sure, because the fecal tests were not definitive, and I didn’t know much about the giardia ELISA assay (more on this below). However, I learned a valuable lesson that weekend. If you are visiting lakes, ponds and other water sources with your dog, he could contract giardia if you aren’t careful.


The Centres for Disease Control and Prevention describe Giardia intestinalis as a common, microscopic (intestinal) parasite that regularly affects humans, dogs and cats. Common signs and symptoms of giardia infection are diarrhea, gas, abdominal discomfort, nausea and vomiting.

Giardia is found in puddles, ponds, rivers and lakes. It can also be picked up from feces. All it takes is for a dog to drink from a contaminated body of water; come into contact with infected feces from another animal; roll and play in an area of contaminated soil; or lick himself after coming into contact with a contaminated surface. In short, absolutely anything that comes in contact with feces from infected animals can become contaminated with the giardia parasite, and dogs (and humans) become infected when they swallow the parasite. As with many other things, puppies and senior canines are at greater risk for infection than adult dogs.


Giardia is a stubborn organism. It is difficult to diagnose and kill. It can infiltrate the upper small intestine, breaking down the dog’s immune defenses. It can even find its way into the liver, where it invades the biliary tract.

Dogs with giardia may have greenish foul-smelling diarrhea. It can be explosive in nature, covered in mucus, and there may be blood in it too. Diarrhea can persist for several days, and may go so far as to cause dehydration, weight loss through inappetence, and lethargy. It could even cause malabsorption because this parasitic infection can pack a wallop, making it difficult for dogs to absorb valuable nutrients from the food they are eating.

On the other hand, the diarrhea may come and go and become a chronic problem, making it even more difficult to deal with. It is also possible for dogs to be infected with the parasite and show no signs or symptoms of illness.


First, we need to understand the life cycle of the giardia organism. For example, a dog ingests an infected cyst through contaminated water. The organism moves around and attaches to the wall of the intestines, where it can reproduce. The parasites encase themselves in cysts, pass through the body in feces, and go on to contaminate other areas.

Testing conducted by a veterinary clinic’s in-house laboratory has been found to be less effective than testing done by standardized equipment at labs like Antech and Idexx. The giardia parasite is not continuously being shed in the feces, so you can be faced with intermittent cyst-free stools. If you think your dog has been infected by the giardia parasite, request an ELISA or PCR test. The fecal antigen test can tell you a story that a fecal floatl may not.

An ELISA test can be giardia positive for up to six months following treatment, because the antigens need to clear the system. The SNAP Giardia Test by Idexx Labs detects soluble giardia antigens. It is the first USDA-approved in-clinic rapid assay for the detection of the giardia-solution antigen, and can be used as an adjunct to a fecal fl oat parasitic diagnosis.

Drugs with anti-protozoal activity such as fenbendazole and metronidazole are used for the treatment of giardia, but they do not show 100% efficacy. As well, super-infections can occur, or dogs can become persistent carriers. Once upon a time, there was a giardia vaccine on the market, but in 2006, the American Animal Hospital Association Guidelines listed it as “not recommended”.


Guarding your dog against giardia involves a preventive program that includes helping him maintain a healthy and strong gastrointestinal system.

1. If you are visiting different bodies of water with your dog, you may want to consider grapefruit seed extract. I am never without it, at home or on the road.

Grapefruit seed extract (GSE) is considered one of nature’s antiseptics. It can be used both topically and internally. Its use began back in the 1970s, when immunologist Dr. Jacob Harich was looking for a natural, non-toxic alternative to antibiotics that would help the body resist bacteria, viruses, parasites and fungi. He found what he was looking for in the seeds and connecting tissue of the grapefruit.

GSE is great for diarrhea, and treats a variety of parasites and viruses. It exhibits significant anti-microbial activity at low concentration. When my dogs experience loose stools or diarrhea, I reach for the GSE right away. The dosage is one drop per ten pounds body weight, or one capsule for every ten pounds body weight, three times per day.

When we’re on the road, and are not sure about the safety of the water supply we will be using, we simply add a couple of drops of GSE to our dogs’ food. It has really made a difference.

2. Oil of oregano is often referred to as “the cure in the cupboard.” “Oil of oregano, like all essential oils, contains a wide range of substances,” writes Dr. Cass Ingram in The Cure is in the Cupboard. “One well-studied compound that predominates in the oil is a substance called carvacrol, a type of phenol. Carvacrol is found in only a few herbs, notably, oregano and savory. Phenols are potent antiseptics. In fact, a synthetic phenol, known as carbolic acid, was used as the standard by which all other antiseptics were measured, for much of the 20th century. As late as the 1950s, carbolic acid was the primary antiseptic used for sterilizing instruments prior to surgery and was the main antiseptic used in hospitals.”

Generally, I use two to three drops of oil of oregano, and simply add it to my dogs’ food. Many people double the dose, when they know they are going to be taking their dogs to a place where infection may be a risk. One bottle lasts for ages and ages. It is also a great addition to homemade treats, like the one included with this article.

Other preventive measures include not letting your dog drink from streams, ponds and lakes, and keeping him away from the feces of other animals. If he loves to swim, of course, it’ll be difficult to stop him from ingesting the water, but if you keep some GSE and oil of oregano on hand, you can help stave off any unpleasant GI upsets that might cut your vacation short.