Giardia is a microscopic parasite that lives in the intestines of both humans and animals. The species Giardia duodenalis (also called G. intestinalis or G. lamblia) is the one most often found in dogs.
It cannot be seen with the naked eye but can cause intestinal upset, especially in puppies, older dogs, or those with weaker immune systems.
Giardiasis is classed as a zoonotic infection, meaning it can occasionally spread between animals and people. Seven genetic types (A–G) are known. Types A and B can infect humans, while all can infect animals.
The parasite has two forms:
- Trophozoite: the active form that lives in the intestines
- Cyst: the dormant, infectious form that is shed in faeces and survives for long periods in the environment
Dogs pick up infection by swallowing cysts from contaminated sources. Common routes include:
- Drinking from puddles, ponds, or streams
- Licking contaminated fur or paws
- Eating food or objects soiled with faeces
- Contact with infected dogs in kennels, parks, or shelters
Cysts survive well in cool, damp areas, so dogs that spend time outdoors or in shared spaces are at higher risk.
Giardia infection may cause no visible signs or range from mild to severe illness. Typical symptoms include:
- Intermittent or chronic diarrhoea (often soft, greasy, or foul smelling)
- Weight loss despite normal or good appetite
- Vomiting
- Bloating or abdominal discomfort
- Lethargy
- Dehydration
- Dull or poor coat condition
Some dogs appear healthy but still carry the parasite, so testing is the only way to confirm infection.
Accurate testing is essential because cysts are shed intermittently. The most reliable diagnostic methods are:
- Antigen testing: detects Giardia proteins in faeces even when cysts are not visible
- qPCR (quantitative PCR): identifies and measures Giardia DNA for early, precise detection
Microscopic checks can still be used but may miss infections. Antigen and qPCR testing provide consistent results and help confirm clearance after treatment.
Treatment targets the parasite and supports recovery. The most commonly prescribed medicines are Fenbendazole and sometimes Metronidazole.
Always complete the full course, even if your dog seems better before it ends. Stopping early can lead to relapse or resistance. After treatment, your vet may recommend a follow up test to confirm the infection has cleared.
Maintain good hygiene throughout and after treatment to reduce the risk of reinfection.
You can lower the chance of infection by:
- Providing clean, fresh water and avoiding natural water sources
- Picking up faeces promptly and disposing of them safely
- Bathing your dog after exposure to communal areas
- Cleaning bowls, bedding, and living spaces regularly
- Avoiding overcrowded areas where outbreaks have been reported
Giardia can occasionally pass between dogs and humans, though this is uncommon. Most human infections come from contaminated water or food.
Wash hands after handling pets or cleaning up faeces. Families with young children, elderly members, or anyone with reduced immunity should take extra care.
If your dog is diagnosed with Giardia:
- Begin treatment as advised by your vet
- Wash hands thoroughly after contact or cleaning
- Clean and disinfect bedding, bowls, and surfaces daily
- Bathe your dog at the start and end of treatment
- Retest after treatment to confirm clearance
Reinfection can occur, especially in multi dog homes, so keep hygiene routines consistent.
Giardia is a common intestinal parasite but is manageable with accurate testing, effective treatment, and careful hygiene. If you notice signs such as diarrhoea or weight loss, arrange testing promptly. Early action helps protect your dog and others from reinfection.
