What is giardia in dogs?

VCA describes Giardia as a microscopic, single-celled organism with two forms. The feeding form lives in the intestine, attaches to the gut wall and is fragile. The cyst form is tough, is passed in the stool, and can infect another animal as soon as it leaves the dog. A dog that swallows cysts starts passing new ones about 5 to 12 days later, which is why a case often surfaces a week or two after the outing where it began.

It is common. The Merck Veterinary Manual cites survey estimates of around 10 to 30 percent of dogs infected at any one time, with higher rates in younger animals, and notes that infection can be present without any clinical signs. In other words, plenty of healthy-looking adult dogs carry it. VCA adds that cysts in the stool of a healthy adult dog are generally treated as a passing, insignificant finding; it is puppies and weakened dogs that tend to become ill.

VCA lists sudden, foul-smelling diarrhea, diarrhea that comes and goes, weight loss, fatty or greenish stool, blood or mucus in the stool, vomiting and low energy, and says signs can last for weeks. Merck notes that the diarrhea is often continual or intermittent, particularly in puppies. Any dog with diarrhea that does not settle, and any puppy with diarrhea at all, should see a vet; the CDC's advice for pet owners is to contact a veterinarian when diarrhea is not going away.

Testing has a known blind spot. Merck explains that cysts are passed intermittently, so an infection can be missed, and that several stool samples may be needed, for example three collected over three to five days. VCA notes that a routine stool test may miss Giardia, and that clinics often use a special flotation solution or an antigen test instead. Treatment is your vet's decision, and VCA advises a retest two to four weeks after treatment ends.

The CDC says you are unlikely to get Giardia from a dog or cat, because the type that usually makes people sick is not the same type that infects pets, and Merck describes transmission from animals to people as relatively rare. VCA still advises extra care for anyone who is immunocompromised or having chemotherapy, especially when handling stool. Ordinary hygiene covers most households: wash your hands, use a bag or gloves for pick-up, and keep your dog's bowls and toys clean.

Other dogs in the household are a different matter. The CDC tells owners to mention every pet to the vet, even healthy ones, because they may need treatment too, and Merck notes it is often unclear whether a returning case is a treatment failure or a reinfection. Washing and drying bedding, bowls and toys regularly, removing stool at least daily, and keeping a sick dog away from creeks, ponds and lakes all cut the chance of the parasite circling the house again.