giardia (duodenalis, lamblia)

Our pets can be hosts for a wide range of parasites. Some of these parasites are harmless to humans, but others can cause serious illness if we become infected. Many of these infectious parasites are transmitted via the feces of our pet dogs (or cats), making it important to understand how these parasites live, breed, and especially, the best ways to prevent our pet’s environment from becoming infective and causing a health-risk to us. One such parasite is Giardia, which can cause severe intestinal problemsOur pets can be hosts for a wide range of parasites. Some of these parasites are harmless to humans, but others can cause serious illness if we become infected. Many of these infectious parasites are transmitted via the feces of our pet dogs (or cats), making it important to understand how these parasites live, breed, and especially, the best ways to prevent our pet’s environment from becoming infective and causing a health-risk to us. One such parasite is Giardia, which can cause severe intestinal problems.

Giardia is not a worm, bacteria or virus. Rather, it is a single-celled parasite, a protozoan that in its adult form, lives in your dog’s intestine. It infects adult dogs but more frequently infects puppies. It is the most common internal parasite found in dogs. Dogs become infected when they swallow Giardia present in water or other substances that have been soiled with contaminated feces. It is unclear whether the protozoans are a single species or several species, each with a specific host. However, it is clear that Giardia is an opportunistic parasite of dogs which can infect several other species of animals, including humans. Infection with Giardia is called ‘giardiasis.’

Unfortunately, there is much about the life cycle of Giardia that we do not know. 

Giardia is unlike many other dog parasites in that the time between ingesting the parasite and the beginning of the disease is very short (5 to 14 days). The lifecycle begins with an infected dog shedding inactive (dormant) cysts into the environment in their feces. It is important to realise that these cysts can remain viable for several weeks or months in cold, wet environments. This means that areas littered with feces should be avoided and piles should be removed from the environment as soon as possible.  Although the cysts are expelled in the feces, once these are deposited, the cysts often contaminate water sources which are the most common route of infection.

Once ingested by your dog, the cysts are moved to the intestine, open, become activated and develop into the mobile form, known as the “trophozoite”. This is a pear-shaped organism with a long hair-like flagellum (tail) that whips back and forth, propelling the trophozoite about within the intestines. If your dog is healthy, trophozoites can live in the lower digestive tract for several years. They attach to the intestinal wall and reproduce by dividing in two. After a number of divisions, some of these develop a wall around itself, thereby becoming the cysts which are passed out in the feces. The Giardia in the feces easily contaminate the environment, very commonly the water, thereby providing a route of transmission to infect other animals and people. 

Giardia is found throughout the world and can be highly prevalent in dog environments.  Up to 50% of young puppies will develop this infection.  Households with multiple dogs are particularly at risk, and up to 100% of dogs housed in kennels will develop the disease due to closely shared living spaces and the repeated exposure to the cysts.
 

Many healthy adult dogs infected with Giardia do not get any disease, however, young puppies or adults with a compromised immune system can become very ill and death can occur if not treated. Symptoms are usually easier to detect in younger dogs than in older dogs.   The symptoms may be sudden, temporary, non-continuous, or ongoing.  The disease caused by Giardia infection is called Giardiasis, although it is sometimes known as Beaver Fever because beavers are known carriers of Giardia.  The disease may result in the following symptoms –

Eliminations

• Watery diarrhea which may contain mucus, be tinged green and frothy
• Feces that are soft, light-colored, greasy and may contain blood
• Feces have an extremely repugnant odor
• Vomiting is a rare symptom, but can happen in dogs with severe bowel inflammation

Appearance of the dog

• Weight loss
• Poor condition
• Dehydration
• Poor coat quality

The organism is primarily detected in the feces. A fecal smear or fecal flotation test is normally sufficient to test for their presence. Diagnosis requires microscopic inspection of feces to determine the identity of the protozoan. Similar examination of soft feces may reveal the presence of active trophozoites, and cysts may be found in firm feces. The number of cysts varies on a daily basis so detection will require collecting and examining samples over 3 to 4 days.

Approximately 5% to 10% of dogs either have Giardia infection (symptomatic) or have it but do not show any clinical signs (asymptomatic).