Giardia in Dogs and Cats: Symptoms, Treatment and Prevention

Giardia is a microscopic parasite that lives in the intestines of dogs and cats. Many infected pets show no signs at all. Others get diarrhoea that comes and goes.

What Giardia is

Giardia is a single-celled parasite. It lives in the small intestine and passes out in faeces as cysts. The cysts are infectious straight away, and only a few are enough to infect another animal. Infected pets can shed cysts for weeks or months, which is why cleaning matters as much as medicine.

How pets catch it

Pets swallow cysts from contaminated ground, food or water, or by licking contaminated fur. Giardia is most common where many animals share space, such as kennels, shelters and pet shops, and young animals are more exposed. Puddles, ponds and shared water bowls can carry cysts.

Symptoms

• Soft, watery or greasy diarrhoea, often with mucus and a strong smell
• Diarrhoea that comes and goes
• Weight loss and a dull coat
• Tiredness
• Occasional vomiting

Many pets have no symptoms but still shed cysts.

Diagnosis

Your vet will ask for a fresh faecal sample. Tests include looking at the sample under a microscope, an antigen test (ELISA) and PCR, which detects the parasite's DNA. Cysts are shed on and off, so a single negative test doesn't rule Giardia out, and the vet may ask for samples over several days. Plenty of healthy pets also test positive, so the vet reads the result together with the symptoms.

Treatment

Vets generally treat pets that have symptoms. A healthy pet that tests positive often doesn't need medicine, though the vet may treat it if a young child, an elderly person or someone with a weak immune system lives in the home.

• Fenbendazole is the usual first choice, given for 3 to 5 days.
• Metronidazole is kept for stubborn cases, because it can cause side effects, especially in small cats and kittens.
• The vet may also change the diet.

Finish the whole course, even if the diarrhoea stops. If signs continue, the vet may retest soon after treatment ends. A positive test 2 to 4 weeks later can mean the pet has caught Giardia again from its surroundings.

Cleaning at home

• Give your pet a bath on the last day of treatment, with particular attention to the rear end, to wash off cysts. Your vet may suggest a chlorhexidine shampoo.
• Pick up faeces every day and put it in the bin.
• Wash bedding at 60 °C or higher.
• Clean floors, bowls, litter trays and toys, then let them dry fully. Steam cleaning works too. Ask your vet which disinfectant to use.
• Soil, grass and standing water are hard to decontaminate, so keep your pet away from the same spots while it recovers.

Prevention

• Offer fresh water, and discourage drinking from puddles and ponds.
• Pick up after your dog straight away.
• Keep the fur around the rear end clean.
• Take extra care in places where many animals gather.

Can people catch it from pets?

The risk is very low. The forms of Giardia that usually infect dogs and cats rarely infect people. The reverse can happen, since human forms can infect pets. Wash your hands after handling your pet and after cleaning up. If you get stomach symptoms, see your GP.

When to see a vet

Contact the vet if your pet has:

• Diarrhoea that lasts more than a day or two, or keeps returning
• Bloody or severe diarrhoea
• Repeated vomiting
• Signs of dehydration, such as dry gums or sunken eyes
• Weakness or tiredness
• Refusal to eat or drink
• Symptoms that get worse during treatment

Puppies and kittens can become unwell quickly. If symptoms are severe outside our opening hours, contact an emergency vet clinic.

If you have several pets, tell the vet. The vet decides which ones need testing or treatment.

Book a visit at the clinic

Our veterinary service can take a faecal sample, send it for testing, treat Giardia and advise on cleaning at home. We're open Monday, Thursday and Friday 10:00 to 16:00, and Tuesday and Wednesday 09:00 to 17:00. Contact the clinic to book.