Last updated: 27 September 2026
Giardia is a single-celled intestinal parasite that typically causes recurring, pale, mucousy and foul-smelling diarrhoea in dogs, while the dog often does not seem seriously ill. The infection can be detected from a fresh stool sample with an antigen rapid test in 5–10 minutes. In puppies, or with persistent or bloody diarrhoea, however, you always need a vet.
Many owners suspect a change of food, a "sensitive stomach" or stress, when in fact this stubborn parasite is often behind it. In this article we describe how Giardia spreads, what symptoms it causes, what the stool of a dog with Giardia looks like, how you can test at home and when a vet is essential. Treatment and reinfection are covered in a separate article: Treating Giardia in dogs.
What is Giardia and how is it transmitted?
Giardia is a single-celled parasite that lives in the small intestine of dogs and cats and is shed in the faeces as microscopic cysts. The cysts are hardy in the environment: in cool, damp conditions they can remain infectious for weeks or even months (Merck Veterinary Manual).
The main routes of infection:
- licking up infected faeces (its own or another animal's),
- drinking from puddles or standing water,
- shared bowls, toys or beds used by an infected animal,
- contaminated soil, water or surfaces in kennels, shelters or dog parks.
Giardia is especially common in puppies, shelter and rescued street animals, multi-pet households, and wherever many dogs share a small space (boarding kennels, dog training schools).
What are the symptoms of Giardia in dogs?
The most characteristic sign is fluctuating, recurring diarrhoea: the stool may be fine for days, then gets worse again. Typical symptoms:
- soft, mucousy, foul-smelling diarrhoea, often with paler stool,
- normal stool at times, then diarrhoea again ("better one day, worse the next"),
- bloating, wind, abdominal discomfort,
- weight loss or slow growth, especially in puppies,
- dull, lacklustre coat, poorer general condition,
- occasionally mild vomiting, although diarrhoea usually dominates.
Many dogs carry Giardia without symptoms but still shed cysts, which is why screening is especially important in multi-pet households and shelters. Cats can show similar symptoms – read more here: Giardia in cats.
What does the stool of a dog with Giardia look like?
Giardia stool is typically soft or mushy, pale, mucousy, strong-smelling and often greasy-looking, and the diarrhoea can be continuous or intermittent (Merck Veterinary Manual). The type of stool tells you a lot, but on its own it is not a diagnosis:
| Type of stool | More likely cause | What to do |
|---|---|---|
| Pale, mucousy, foul-smelling, greasy, coming and going | Giardia | Giardia rapid test on a fresh sample; see a vet if positive |
| Bloody or very watery, with vomiting and lethargy (especially in puppies) | Parvovirus | See a vet immediately – more here: parvovirus in dogs |
| Sudden-onset, watery, usually milder diarrhoea | Canine coronavirus | Combined test (CPV/CCV/Giardia); see a vet if it gets worse |
| One-off diarrhoea after a food change or scavenging, dog otherwise well | Dietary cause | Monitor for 1–2 days; see a vet if it does not settle or gets worse |
What is the incubation period of Giardia?
It usually takes 3–10 days from infection until cysts are shed (Merck Veterinary Manual); symptoms may appear after that, but many dogs remain symptom-free. Shedding can last weeks or months (ESCCAP) and is not continuous: on some days hardly any cysts end up in the stool.
Why is Giardia confused with food allergy?
The symptoms of Giardia closely resemble food or protein sensitivity, stress-related diarrhoea and a "sensitive stomach". Many owners switch food, give probiotics or try home-cooked meals, and things may improve temporarily before the problems come back. Meanwhile Giardia is still there and, especially in puppies, can affect development.
That is why every dog with long-lasting or recurring diarrhoea should be specifically screened for Giardia, rather than just being treated "blindly".
How does Giardia spread and why does it keep coming back?
The most common reason is reinfection: cysts survive for weeks in the environment (bed, garden, bowls) and on the dog's coat, especially around the hindquarters, so the dog can swallow them again during or after treatment. An untreated companion animal can also reinfect it. That is why treatment must always be combined with cleaning and bathing. You can find a detailed cleaning and bathing plan here: Treating Giardia in dogs – why does it keep coming back?
Is Giardia dangerous to humans?
Dogs mostly carry Giardia types (genotypes C and D) that mainly infect dogs, so transmission from dogs to people is rare; people usually catch it from other people (CAPC). However, a type that can infect humans (A) can also occur in dogs, so hygiene matters:
- wash your hands thoroughly after picking up faeces or cleaning the litter tray,
- children should not play where there may be fresh animal faeces,
- clean the home, the dog's bed and the run regularly.
If someone in the family has persistent diarrhoea while there is a Giardia-positive animal in the house, it is worth mentioning this to your doctor.
How can I test my dog for Giardia at home?
With a fresh stool sample and an antigen rapid test: mix the sample in the buffer solution, put a few drops onto the test cassette and read the result after 5–10 minutes. The test can be used for both dogs and cats.
- Sampling: take a fresh stool sample with the swab provided.
- Mixing: place the swab in the tube containing the buffer solution and mix thoroughly.
- Applying: put 3–4 drops from the tube into the sample well of the cassette.
- Waiting: wait 5–10 minutes; after 15 minutes the result is no longer valid.
- Reading: the control (C) line must always appear.
| What you see | Result | What does it mean? |
|---|---|---|
| Both C and T lines appear | Positive | Giardia antigen detected; talk to your vet about treatment. |
| Only the C line appears | Negative | No Giardia detected in this sample. If symptoms persist, repeat with a new sample within 2–3 days, as shedding is intermittent. |
| No C line | Invalid | The test did not work properly; repeat with a new cassette. |
According to the manufacturer's validation against PCR on 300 samples, the MancsLab Giardia Ag rapid test has a sensitivity of 98.57% and a specificity of 99.13%. If parvo is also a possibility behind a puppy's diarrhoea, the 3-in-1 (CPV/CCV/Giardia) or the 4-in-1 test screens for several pathogens at once.
How long does Giardia take to clear, and when can you retest?
Treatment must always be prescribed by a vet: typically a medication course lasting several days, together with bathing the dog and thoroughly cleaning the environment. Symptoms usually ease during the course, but lasting success depends on preventing reinfection.
Important: after successful treatment the antigen test can stay positive for some time, so straight after treatment it is not suitable for deciding whether the course worked (CAPC). Your vet will decide on the follow-up check – usually a microscopic stool examination. If the diarrhoea returns weeks later, a new rapid test helps you find out whether Giardia is back.
When should you take your dog to the vet immediately?
| Warning sign | Why is it urgent? |
|---|---|
| Bloody or black, tar-like stool | May indicate severe intestinal damage, bleeding or parvo. |
| Repeated vomiting, the dog cannot even keep water down | It can quickly become dehydrated. |
| A lethargic puppy with diarrhoea | In puppies, the condition can deteriorate within hours. |
| Fever, marked weakness, loss of appetite | Points to more than a simple intestinal parasite; an examination is needed. |
| Diarrhoea lasting longer than 2–3 days or getting worse | The underlying cause needs to be clarified by a vet. |
More on diarrhoea warning signs: Dog diarrhoea: when is it harmless and when is it an emergency? All tests suited to diarrhoea in one place: diarrhoea in dogs and cats – which test do you need?
Frequently asked questions about Giardia
Can Giardia go away on its own in dogs?
Symptoms sometimes improve temporarily, but without treatment the infection often persists for weeks or months, during which the dog sheds cysts and can infect other animals. Whether and how to treat is up to your vet.
The test is positive but my dog has no symptoms. Does it need treatment?
Not necessarily. According to ESCCAP, many clinically healthy dogs and cats can test positive, and not all of them need treatment. For a positive animal without symptoms, your vet will decide – especially for puppies, weakened animals or multi-pet households.
Is it enough to treat only the dog with diarrhoea?
In multi-pet households Giardia is often present in several animals, even without symptoms. In such cases vets often recommend examining or treating all animals living together so that they do not keep reinfecting each other.
How should I clean if there is Giardia in the house?
During treatment, wash beds and blankets at 60 °C or higher, clean bowls, toys and floors and then let them dry completely, and pick up fresh faeces immediately. ESCCAP also recommends washing the dog's hindquarters with a chlorhexidine shampoo. A grassy garden cannot be disinfected and should be considered contaminated for at least a month.
How accurate is the home Giardia test?
According to the manufacturer's validation against PCR on 300 samples, the MancsLab Giardia Ag rapid test has a sensitivity of 98.57% and a specificity of 99.13%. Because cyst shedding is intermittent, if suspicion is strong it is worth repeating a negative result with a new sample within 2–3 days.
Summary
Recurring, pale, mucousy and foul-smelling diarrhoea is often caused by Giardia. A home antigen rapid test gives you an answer in 5–10 minutes, but treatment and follow-up are always decided by your vet, and the course must be combined with cleaning and bathing, otherwise the infection may return.
Sources
- Companion Animal Parasite Council (CAPC): Giardia – guidelines. capcvet.org
- ESCCAP: Giardia infection in dogs and cats (fact sheet). esccap.org
- Merck Veterinary Manual: Giardiasis in Animals. merckvetmanual.com
- Manufacturer's validation data (Giardia Ag rapid test). product page
Important: this article provides general information and does not replace veterinary advice. Treatment, dosage and follow-up checks must always be decided by a vet. MancsLab rapid tests are intended for preliminary screening at home.