Giardiasis is a dog disease caused by Giardia, protozoa found in the small intestine of dogs and cats in many parts of the world. Protozoa are one-celled organisms and we still know comparatively little about them. The protozoa causing Giardiasis in dogs is referred to as Giardia canis.

As mentioned above, we still now very little about protozoa and Giardia is not an exception. Veterinary experts are still not sure about the best way of treating Giardiasis in dogs, or even why some dogs develop Giardiasis in the first place. Most experts today believe that Giardia infections are very common but that only a very limited number of dogs ever display any symptoms.

It is also unsure whether you can catch Giardiasis from your infected dog and strict hygiene is therefore recommended when caring for a dog with suspected or confirmed Giardiasis. What we do know for sure is that humans can be infected by the Giardia parasite by drinking contaminated water and develop Giardiasis.

Transmission of Giardiasis to dogs

A dog can become infected with Giardia by eating or drinking a cyst from the protozoa. When the cyst reaches the small intestine of the dog, it will open and release the active form of the Giardia protozoa. This form is called the trophozoite. Giardia trophozoites use flagella to move around; a type of hair that can be used to whip back and forth, thereby causing mobility. The trophozoites attache themselves to the intestinal wall of the dog where they begin to multiply by division. Eventually, new cysts will be formed by how, after how long a period of time and where in the body of the dog the cysts are formed is still not known. The cysts will leave the dog through its faeces and are now ready to infect another dog – or any other susceptible animal. 

Giardiasis symptoms in dogs

In most dogs, a Giardia infection will not lead to disease. When the protozoa do cause disease, the primary Giardiasis symptom in dogs is diarrhoea. Younger dogs seem to be more prone to developing Giardiasis symptoms than adult dogs. Diarrhoea brought on by Giardiasis can be acute, intermittent or chronic. Most dogs will retain their appetite, but they can still loose weight due to persistent diarrhoea. Inside the dog, Giardiasis will damage the intestinal lining and make it difficult for the intestine to absorb nutrients from the food. Giardiasis will also interfere with the overall digestion process. Dog owners can notice that their dog's faeces look strange, often pale and greasy. The faeces can also give off an odour that is even worse than the one emitted from normal dog faeces.

Giardiasis treatment for dogs

Since we still know so little about Giardiasis, it is hard to give any definite guidelines regarding Giardiasis treatment for dogs. Different veterinarians use different treatments, and there is also the question about when Giardiasis treatment should be started. Since a lot of dogs carry Giardia protozoa without developing any signs of illness, it is probably not a good idea to start treating all dogs that happen to test positive for Giardia. Others argue that since Giardia protozoa might be transmitted from dogs to man, all cases of Giardia in dogs should be promptly treated to prevent human illness. There are also quite a large number of cases where veterinarians suspect Giardiasis but fail to locate the Giardia protozoa using the available testing methods. The opinion regarding such cases varies from veterinarian to veterinarian, but many will provide the dog with Giardiasis if the dog is ill, the symptoms point towards Giardiasis and other probable causes have been ruled out.

It should be noted that quite a few of the popular Giardiasis treatments for dogs have not been approved for use in dogs by the United States Food and Drug Administration. It is also possible that the available treatments only remove the cysts from the faeces of the dog, without actually killing the Giardia living inside the intestines of the dog. More research on dogs with Giardiasis is necessary before anyone can know for sure.

Fenbendazole is an antiparasitic drug capable of killing several types of intestinal worms, and it has proven helpful in Giardiasis control as well. Fenbendazole can be used alone, but many vets prefer to combine it with Metronidazole when treating dogs with suspected Giardiasis. Metronidazole is known to be effective against several types of bacteria that causes diarrhoea, so in cases where Giardia is not the culprit Metronidazole might be able to take care of the problem by killing bacteria. Metronidazole is also around 60-70% effective in eliminating Giardia from infected dogs. A problem with Metronidazole is its liver toxicity. It is also very bitter and dogs can refuse taking it orally. If you have a pregnant bitch, Metronidazole should ideally not be used since it is suspected of causing physical defects in developing embryos.

Before Fenbendazole, vets often used Quinacrine hydrochloride to treat Giardiasis in dogs, but Quinacrine hydrochloride is not as effective as Fenbendazole and many dogs react to the treatment with vomiting, loss of appetitive, fever and weakness.