Giardiasis is an intestinal infection caused by Giardia, a microscopic parasite that can affect dogs and cats. It is particularly common in young animals, especially puppies and kittens, although adult pets can also become infected.
The parasite lives in the intestine and can cause digestive problems, particularly diarrhoea, although many infected pets show no signs of illness. Pets become infected by swallowing Giardia cysts from contaminated faeces, water, food or the environment. Because the cysts can survive in the environment and are infectious as soon as they are passed, infection can spread readily between animals, particularly where several pets live together.
The symptoms of giardiasis can vary. Some infected pets show no signs at all, while others develop digestive problems.
Common symptoms include:
Diarrhoea, which may come and go
Soft, pale or greasy-looking stools
Particularly foul-smelling faeces
Mucus in the stools
Weight loss or poor weight gain, particularly in young animals
Contact your vet if your pet has persistent or recurrent diarrhoea, particularly if they are also vomiting, losing weight or seem unwell.
Puppies and kittens can become dehydrated quickly, so it is especially important to seek veterinary advice if a young pet has diarrhoea, is not eating or drinking normally, or appears lethargic.
Giardiasis cannot be diagnosed based on symptoms alone, as many other conditions can cause similar digestive problems. Your vet may recommend testing a faecal sample to look for Giardia.
As the parasite is not always present in every stool sample, your vet may ask you to collect samples over several days or recommend repeat testing.
Treatment for giardiasis will depend on your pet's symptoms and the results of diagnostic testing. Your vet may prescribe medication to treat the infection and recommend supportive care if your pet is unwell or dehydrated.
Some pets may need more than one course of treatment. If diarrhoea is severe and your pet becomes dehydrated or otherwise unwell, more intensive treatment may be required.
Good hygiene is also an important part of treatment, as pets can become reinfected from contamination in their environment. Your vet may advise you to clean your pet's bedding and living areas regularly, remove faeces promptly and, in some cases, bathe your pet to remove contamination from their coat.
Follow your vet's instructions carefully and complete any prescribed treatment as directed.
Good hygiene can help reduce the risk of giardiasis and prevent reinfection.
You can help by:
Picking up and disposing of faeces promptly
Washing your hands after handling your pet or cleaning up faeces
Cleaning food and water bowls regularly
Providing fresh, clean drinking water
Avoiding potentially contaminated water where possible
Washing bedding and cleaning contaminated areas regularly
Following your vet's advice about bathing your pet and treating other pets in the household
In homes with several pets, kennels and other shared environments, careful hygiene is particularly important.
Some types of Giardia can infect both animals and people. However, the risk of transmission from dogs and cats to people is considered to be very low.
Good hygiene is still important. Wash your hands thoroughly after handling an infected pet, cleaning up faeces or touching potentially contaminated bedding, bowls or other items. If you develop diarrhoea or other symptoms after contact with an infected pet, speak to your GP.
The outlook for most otherwise healthy pets with giardiasis is generally good with appropriate treatment and good hygiene. Many pets improve within a few weeks, although some may need more than one course of treatment.
Puppies and kittens can be more vulnerable to the effects of ongoing diarrhoea. Young animals can become dehydrated quickly, and prolonged illness may affect their appetite, weight gain and growth. Prompt veterinary advice and treatment are therefore particularly important in young animals.
Once a pet has recovered, ongoing problems are uncommon. However, if symptoms continue, worsen or return after treatment, contact your vet, as further investigation may be needed.
Written by Gillian Burkhill, Veterinary Surgeon, Animal Trust Vets CIC | Published September 2026 | Review date September 2029 | This advice is for UK pets only and is not a replacement for seeing a vet
