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Giardia
A microscopic gut parasite. Dogs catch it by swallowing cysts from contaminated poop, water, food or surfaces.
Go to the vet now if…
- There's blood in the stool, or it's black and tarry (giardia rarely causes blood, so it may be something else).
- Repeated vomiting, or vomiting together with diarrhea.
- Very tired or weak, not eating, or not drinking.
- Your puppy is very young or very small, or not fully vaccinated (it could be parvovirus).
- The diarrhea lasts more than 24 hours.
How you notice it
- Many dogs show no signs at all.
- Diarrhea that lingers or comes and goes, with soft, pale or mucus-covered stools.
- Very smelly stools and more gas than usual.
- Occasional vomiting.
- Weight loss, or not gaining weight as expected.
- In bad cases, tiredness and a smaller appetite.
What to do
- Call your vet and say how long the diarrhea has lasted, what the stools look like, and whether your puppy is eating and drinking.
- Bring a stool sample. Your vet may ask for several from different days, because giardia doesn't show up in every sample.
- Pick up poop right away, put it in the trash, and wash your hands.
- Clean bedding, floors and bowls and let them dry fully (cysts don't survive drying). Wash bowls with boiling water.
- Bathe your puppy with shampoo when your vet says (usually at the end of treatment) to wash cysts off the coat.
- Give the treatment exactly as prescribed, for all the days. If diarrhea comes back, tell your vet: reinfection can happen.
Does it spread?
- To other dogs: yes
- To people: rarely
Yes, between dogs, through poop. To people, very rarely: dogs usually carry types of giardia that differ from the ones people get. Still, wash your hands.
How to prevent it
- Pick up poop every day, at home and on walks.
- Always offer clean water and don't let your puppy drink from puddles.
- If your puppy joins a home with other pets, ask your vet about a stool test.
Sources
- Disorders Caused by Protozoa in the Digestive System of Dogs - Dog Owner Version (Patton S, Constable PD; updated Sept 2024)
- CAPC Guidelines: Giardia (dogs and cats; updated 3 Aug 2026)
- ESCCAP Guideline 06: Control of Intestinal Protozoa in Dogs and Cats (3rd edition, March 2025)
- Diarrhea (canine health topics; edited and updated 3/2024 by Riney Canine Health Center veterinarians)
- Diarrhoea in dogs (PDSA Pet Health Hub; written by vets and vet nurses, May 2023)
- Why does my puppy have diarrhoea?
- 13 Animal emergencies that require immediate veterinary consultation and/or care
- Canine parvovirus (pet owners)
- Nobivac DHPPi lyophilisate for suspension for injection for dogs - Summary of Product Characteristics (last revised Aug 2025, approved Dec 2025)
- MAXIVAC PRIMA DP liofilizado y suspensión para suspensión inyectable para perros - Ficha técnica (RCP rev. 08/2024)
- Vaccine Failure and Other Adverse Events in Animals - Professional Version (Tizard IR; full review Oct 2023, updated Sep 2024)
This is general information, not a diagnosis. Your vet is the one who can tell what's wrong and what to do.