Are antibiotics effective against Giardia cysts?


Giardia are single-celled flagellates. They are found in the intestines of numerous mammals around the world. As zoonotic pathogens, they also pose a threat to humans G. duodenalis (syn. G. intestinalis, G. lamblia) as well as a widespread intestinal parasite in dogs and cats. Along with roundworms, giardia are among the most common parasites in dogs and cats. Hundreds of thousands of infectious cysts are excreted with the animals' feces.

Routes of infection

Infection occurs with infectious cysts via contaminated food, water or smear infections. Flies also play a role in spreading the pathogens and contaminating the food. Just 10 cysts are sufficient as an infectious dose. The cysts released into the environment are immediately infectious. In the host's intestine, the cyst dissolves and releases two protozoa, the trophozoites. These attach to the microvilli of the cells of the intestinal mucosa. Here they multiply by dividing them into two parts. Under favorable conditions, the Giardia can multiply very strongly. At the same time, the transformation into a resistant cyst begins, which then again contains two trophozoites. The cysts are excreted in large quantities (up to 10 million cysts per gram of feces) over a period of 4 to 5 weeks, sometimes even months. This period is extended if infectious cysts are repeatedly taken in from the environment. The excreted cysts remain infectious in cool water (4 ° C) for up to 3 months, in moist soils for up to 7 weeks. Under optimal conditions, these can remain viable for several months.


In dogs, giardia, along with roundworms, are among the most common intestinal parasites. The infestation rate in puppies and young dogs can be up to 70 percent.

The infestation rate is not only influenced by age, but also by how it is kept. If many dogs are kept together, for example in kennels or animal shelters, the risk of infection increases. After the introduction of the parasite, practically any animal can become ill and the number of patent infections can be up to 100 percent.

In cats that tested positive for endoparasites, every second cat was infected with Giardia, as in dogs. 75% of the animals were younger than one year.

This shows the increased relevance of Giardia in enteropathies (intestinal diseases) in dogs and cats.

Clinical symptoms

The trophozoites attach themselves to the intestinal mucosa with their suction disc. This leads to mechanical damage to the microvilli and thus to malabsorption. While giardiosis is almost always symptom-free in adult dogs and cats, in puppies and young animals with foul-smelling, persistent, intermittent or chronic light diarrhea with slimy and rarely bloody additions. Most of the time the feces are very fatty. Some of the animals also vomit.


An infection with Giardia can be determined by means of a fecal sample with the help of special enrichment methods or by means of copro antigen detection.

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Treatment with fenbendazole is the drug of choice. Infected dogs can be treated with fenbendazole at a dose of 50 mg / kg body weight for 3 to 5 consecutive days.
Cats generally respond less well to giardiosis treatment compared to dogs, the reasons for this are unknown. However, fenbendazole is effective at a dose of 50 mg / kg body weight / day.
Regarding the duration of treatment, however, different information is given in the literature, ranging from 3-day to 5-day therapy. Since the recurrence rate due to reinfections is very high, repeat treatments are generally recommended after approx. 2 weeks. However, empirical values ​​show that a shorter repeat treatment interval is often possible for cats, such as a 3-day break between two 5-day treatments. Well-founded scientific studies on this are not available.

To date, no side effects have been observed with treatment with fenbendazole. In contrast, side effects are often observed with treatments with metronidazole.

Due to the high risk of infection and the zoonotic potential for humans, dogs and cats should be examined for this pathogen if Giardia is suspected and treated if positive. The 3-day treatment with the active ingredient fenbendazole from Giardia also simultaneously covers all relevant roundworms as well as the most common tapeworms (taenias) in dogs and cats.

Hygiene measures

Due to the high risk of reinfection, certain hygiene measures must be carried out at the same time as the treatment. This is particularly important in animal shelters or kennels with high infection pressure. This includes thorough cleaning of all faecal contaminated areas using a steam jet (temperature> 60 ° C) and a suitable disinfectant (e.g.Halamid). The areas then have to dry off completely, as the Giardia cysts survive best in cold and damp conditions.
In addition, at least long-haired animals should be shampooed thoroughly because of the very small dose of infection.

Measures that reduce the infection pressure:

  • Treatment of all dogs and cats in the herd

  • Reduction of the contamination of the environment with feces (collect feces and dispose of harmlessly)

  • Removal of fresh feces

  • Eliminate water / feed contaminated with feces

  • Cleaning of contaminated objects (clean food and water bowl with boiling hot water)

  • Clean the litter box daily (hot water, dry well)

  • Detection of reservoirs of infection

  • Especially shampoo long-haired animals after therapy, as the minimum infectious dose is very low and infectious cysts can adhere to the coat

  • Drainage of damp areas

  • Attach the spouts

  • Clean the boxes and the kennel with a steam jet device

  • Dry well after cleaning

  • Disinfection on paved floors

DISIFIN animal from RMP GmbH and Halamid available from ecuphar. Please note the concentration and exposure time specified in the product description.