Almost all dogs will struggle with intestinal parasite infections at some point during their lives—most commonly as a puppy. Giardia is a common intestinal parasite in dogs—affecting adults and puppies equally—because the parasite spreads easily in the environment and can be difficult to detect and treat. Whether you’ve battled previous giardia infections in your four-legged friends or you’ve never heard of the disease, the Animal Hospital of Parkland team shares the facts that pet owners need to know.

Fact #1: Giardia infections are extremely common in dogs

Giardia is a single-celled intestinal parasite that transmits more easily from dog to dog than other parasites, such as roundworms or hookworms. Infected dogs shed Giardia cysts in their stool, and the cysts are immediately infective to other dogs who ingest the them from contaminated water or soil or from sniffing the fur on another dog’s hind end. Studies show that prevalence varies regionally and in specific populations, but as many as 8% to 45% of dogs are infected. Dogs who frequent dog parks generally have a higher incidence than the general dog population, but all dogs are at risk, because the cysts can survive in water or soil for long time periods.

Fact #2: Infected dogs may or may not show illness signs

Many dogs with Giardia become sick with watery diarrhea shortly after infection, but others can host the parasite without developing illness signs, and they become asymptomatic carriers who can intermittently shed cysts into the environment. Identifying and treating all asymptomatic carriers is impractical and close to impossible, which puts dogs in social situations at higher risk for contracting the disease, whether or not any of the dogs are sick.

Fact #3: Humans can also get Giardia, but not likely from your dog

For many years, veterinary teams warned pet owners that their dog or cat could transmit Giardia to human family members, but researchers found that Giardia exist in many different subtypes, and each prefers a different host. This means that most human Giardia infections originate from other humans, and most dog infections come from other dogs. 

Inter-species transmission may be highly unlikely but is still possible, so you should take extra precautions if your household includes young children, older adults, or immunocompromised people. Giardia likes cool, moist environments, so you can help eliminate the cysts by cleaning your home with steam and running linens through warm wash cycles. Every family member should also wash their hands after interacting with infected pets.

Fact #4: Treatment protocols vary, depending on the dog

Treatment is recommended for all infected dogs who show clinical signs, which may include acute, chronic, or intermittent diarrhea. A three- to five-day medication course often resolves symptoms and clears the infection, but some dogs will need a second treatment course. Infections that persist despite several medication courses are treated on a case-by-case basis, depending on the dog’s lifestyle and household and whether our veterinary team believes they are persistent infections or reinfections from ineffective sanitation.

Fact #5: Giardia reinfections are common among dogs

Dogs who clear their initial infection can easily be reinfected if the source remains in the environment. You can take the following steps to prevent reinfections:

  • Bathe your pet on the last treatment day to remove cysts from their fur.
  • Steam-clean the house and wash bedding on warm cycles to inactivate environmental cysts, which prefer cool, moist surroundings.
  • Remove standing water from your yard.
  • Avoid letting dogs dig or roll in off-leash areas frequented by other dogs or wildlife.

Fact #6: Routine parasite testing helps reduce Giardia transmission

A person holds a fluffy dog while sitting at a veterinary clinic. A smiling vet in scrubs, with a stethoscope, sits at a desk, surrounded by a laptop and paperwork in the background.

Several different test types can detect Giardia in your pet’s stool, and each is used in different situations. Routine fecal floatation tests are used to check for Giardia cysts and other parasite eggs under the microscope—this test is recommended for routine screening of asymptomatic pets. In pets with active diarrhea, an antigen or PCR test can detect Giardia particles or DNA not visible on a fecal floatation test. 

PCR and antigen tests are more sensitive for detecting Giardia than fecal floatation tests, but are not recommended as a routine screening tool or for retesting after treatment, because they will remain positive for long periods after an infection has cleared. The best way to determine an active infection is to find cysts in the stool, because these are considered the “infective” stage. 

Don’t let the threat of giardiasis stop you and your dog from enjoying your normal activities. The Animal Hospital of Parkland team recommends fecal parasite screenings at least annually and more frequently for highly exposed social dogs. Contact us to schedule a routine examination and parasite check if your pet is overdue for their regular visit or if they develop diarrhea.