Photograph: Unsplash (free licence).
Quick answer: a study published in PLOS One and reported in October 2026 analysed 157,616 cats and found Giardia in 6.3%. Positive results were more common in autumn (7.7%) and winter (8.1%) than in summer (4.6%), and far more common in kittens under one year (10.7%). To prevent it: remove faeces daily, wash the litter tray and your hands thoroughly and have regular faecal tests done by your vet.
Giardia is a microscopic intestinal parasite that can cause diarrhoea in cats, dogs and people. It does not always cause symptoms, which is why it can easily go unnoticed at home. New research based on North American laboratory data offers useful figures for every cat owner, in Europe too.
What the study found
The researchers reviewed PCR faecal test results from cats in 49 US states and five Canadian provinces, carried out between March 2022 and August 2023.
- 6.3% of the cats tested were positive (9,962 animals).
- Kittens: 10.7% of those under one year were positive, compared with 1.3% of adults.
- Season: 4.6% in summer, 7.7% in autumn and 8.1% in winter.
- It was more common in males and unneutered cats.
- 18.5% of positive cats carried variants (assemblages A and B) that can also infect people. The most common variant was the cat-specific one.
A positive result does not mean the cat will infect its family, but it is a reminder that hygiene at home matters, especially if young children, older people or anyone with a weakened immune system live there.
Symptoms: when to see the vet
Contact your practice if your cat has diarrhoea (sometimes soft, with mucus or foul-smelling), vomiting, weight loss or loss of appetite, particularly if it is a kitten or has just joined your household. Only the vet can confirm the diagnosis with a faecal test and prescribe the right treatment. Indoor-only cats should be included in routine check-ups too.
Litter tray hygiene: what you can do
- Remove faeces every day with a scoop and use bags to dispose of them without touching them.
- Wash the tray regularly with hot water and soap and dry it well before refilling.
- Wash your hands after cleaning the litter tray, even if you wore gloves.
- Keep your cat away from worktops and food preparation areas.
- One tray per cat plus one in multi-cat homes, so dirt does not build up.
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Frequently asked questions
Can my cat give me Giardia?
Some variants can infect people, but the most common one in cats is specific to them. Good litter tray hygiene and handwashing greatly reduce the risk. If in doubt, ask your vet and your GP.
Can an indoor cat have Giardia?
Yes. That is why the study recommends including indoor cats in routine faecal testing too.
How often should I change all the litter?
It depends on the type of litter and the number of cats. As a guide, remove faeces daily, replace the litter completely and wash the tray regularly, following the manufacturer’s instructions.
Keep reading
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- Several cats at home: how many litter trays you need
- Soya cat litter: pros and cons