Giardia in Dogs

My dog tested positive for Giardia. Should I be worried?

Giardia is a microscopic parasite that can cause an intestinal infection in both humans and animals. It is a simple one-celled protozoan, not a worm, bacterium or virus. The parasite occurs worldwide and is a common cause of “traveler’s diarrhea” in people. Campers who drink contaminated water from lakes or creeks may develop “beaver fever,” which is another name for giardiasis in people. Dogs are infected when they drink or stand in water, food or soil that has been contaminated with feces.

Giardia can cause significant illness — including diarrhea, nausea, vomiting and abdominal gas — in animals and people. However, most dogs infected with Giardia have no signs of feeling sick. Some medical personnel even consider the organism to be part of the normal intestinal flora, but younger dogs or dogs with weakened immune systems are more likely to develop symptoms.

The Giardia organism has two forms: The trophozoite is a fragile feeding form that lives in the gastrointestinal tract of infected animals. A hardy cystic form is passed in feces and can survive several months in the environment, especially in water and damp conditions.

How do dogs get Giardia?

Dogs become infected with Giardia when they swallow the cyst form of the parasite. Once the cyst passes into the dog’s intestines, it transforms into the trophozoite and attaches to the intestinal wall to feed. If a large number of parasites are present, damage to the intestinal wall will develop.

Trophozoites reproduce by dividing, and some transform into the cystic form. Eventually, the dog passes infectious cysts in its stool. The time it takes from ingestion of cysts to passage in feces is five to 12 days in dogs. These cysts are immediately able to infect another animal. Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground or drinking tainted water.

When Giardia cysts are found in the stool of a healthy adult dog with normal feces, they are considered a temporary, insignificant finding. In puppies or debilitated adult dogs, the cysts may cause severe, watery diarrhea that may be fatal if left untreated. The likelihood of developing disease increases when large numbers of cysts are present in the environment from fecal contamination. Giardiasis is often seen in densely populated conditions where the sanitation is less than optimal, such as kennels, pet stores or animal shelters.

What are the signs of a Giardia infection?

In cases where these microscopic parasites attach themselves to the intestinal wall, the resulting damage causes a sudden onset of foul-smelling diarrhea. Giardia infections in dogs may lead to weight loss, chronic intermittent diarrhea and abnormal stool. The diarrhea ranges from soft to watery, often has a greenish tinge, and occasionally contains blood and mucus. The signs may persist for several weeks and gradual weight loss may become evident.

The disease is not usually life threatening unless the dog’s immune system is immature or immunocompromised. Many dogs will be asymptomatic carriers and never develop any signs of illness. Younger dogs are more likely to exhibit clinical signs.

How is Giardia diagnosed?

Your veterinarian will need to examine a stool sample. Because Giardia cysts can be shed intermittently in the stool, they might not be seen on a single stool sample. They may require a special zinc sulfate flotation solution, or multiple samples to make a diagnosis. Occasionally, the parasites may be seen on a direct smear of the feces.

A stool sample can also be analyzed for Giardia-specific antigens, which are cell proteins produced by the parasite. A stool sample that is positive for the proteins but negative for cysts indicates recent exposure and not necessarily active infection.

What is the treatment for Giardia?

The goal of treatment is to resolve the diarrhea and other clinical signs. Dogs with no symptoms may not require treatment.

The most common drugs used to treat giardiasis are fenbendazole (Panacur) and metronidazole (Flagyl). These drugs are prescribed for three to 10 days and may be given in combination for dogs with diarrhea that have not responded to either drug alone. Supportive treatment with electrolyte fluids and probiotics may be needed if the dog is dehydrated or the diarrhea is severe.

A low-residue, highly digestible diet may firm up stools during treatment. All infected dogs should be retested two to four weeks following treatment. Because Giardia cysts are infective immediately when passed into the environment, feces should be removed and disposed of promptly. Infected dogs should be bathed regularly to remove cysts from their fur.

Dogs may become re-infected if their surroundings are not properly maintained. Also, if the Giardia is resistant to the medication used or if the medication was not dosed properly, infections may recur.

Can my dog give a Giardia infection to me or my family?

Humans and other species can become infected with Giardia; however, the type of Giardia that normally affects humans is different from the type that infects dogs. For this reason, it is rare for humans to get infected from a strain of Giardia that dogs carry and vice versa.

Washing hands thoroughly with soap and water after handling dogs or infected feces is recommended. Wear gloves when gardening to reduce the risk of coming into contact with infected soil.

Human-to-human transmission is possible, so good personal hygiene is important. Contaminated municipal water supplies are responsible for many outbreaks.

How contagious is Giardia to my other dogs?

Giardia can be easily spread from dog to dog. An infected dog increases the risk of exposing other dogs in the household to Giardia, due to the presence of cysts.

You can limit the risk of spreading the infection by having infected dogs defecate in a separate area, wiping their butt after they defecate, and preventing the dogs from grooming each other. Continue to pick up all feces promptly. Dogs should be fully bathed on the last day of treatment to remove any fecal material and any remaining Giardia cysts in the dog’s fur. Remember to wash your hands after petting your dogs and cleaning up the poop.

How do I clean and disinfect my house if my dog has a Giardia infection?

Common household disinfectants and steam-cleaning are the most effective ways to kill Giardia cysts. Clean the dog’s area, including floors, crates and beds, and wash water and food bowls daily with soap. Disinfect the sink immediately afterward.

Outdoors, Giardia can survive for several months in cold water or soil. Giardia survives longer in moist, cool environments. The cysts on the lawn can only be killed by direct sunlight drying them. Remove any standing water in containers, pool covers or fountains that are not in use.

Do not use bleach or ammonia in your soil or grassy areas. It will not be effective and can potentially be toxic to your dog. Do not allow any new dogs, especially young ones, to enter the yard or outdoor area until the infection has been treated and resolved.