What is giardia?
Giardia is a protazoa (single celled organism) of the giardia species. Infection is known as giardiasis and is characterised by severe diarrhea.
The organism lives the small intestine of a wide range of hosts including humans, dogs and cats. The parasite is found worldwide and is one of the most common enteric (intestinal) parasites in domestic animals. Most infections in healthy adult dogs are subclinical, meaning they are infected with the parasite but displaying no symptoms.
Giardia is of particular significance because it is zoonotic, which means it can be passed from dogs to humans.
How do dogs become infected with Giardia?
Transmission of giardia is by ingesting infective cysts via drinking contaminated water, food or via the fecal-oral route.
Once in the small intestine the cysts break open releasing two trophozoites. These are the active, motile (swimming) form. Trophozoites attach to the cell walls of the intestine feeding. As you can see from the image above, trophozoites have long hair-like structures called flagella which help the protazoa to move around. While in the small intestine, the parasite reproduces asexually (known as binary fission), splitting into two cells.
Eventually the detach from the intestine & move towards the colon, if they have time, they produce a cyst wall, this enables them to survive in the outside environment once they have been passed out of the body (trophozoites are much more fragile). Within this wall the trophozoite divides once, and the mature cyst now containes two trophozoites. The cyst is carried along by the passing fecal stream where it eventually leaves the body when the infected host passes a stool.
Cysts are very hardy and are able to survive for long periods of time in the environment
What are the symptoms of giardia in dogs?
The incubation period of giardia is one to two weeks. Even though some dogs are asymptomatic, they still pass on cysts for months or years.
The most common symptom of giardia is the passage of large volumes of foul smelling, watery or frothy stools. Other common symptoms include:
How is giardia in dogs diagnosed?
Fecal examination - Diagnosis is made by finding the protazoa or it’s cysts in smears of fresh stool. This can be for trophozoites or the cysts. If the stool is watery, the trophozoites may be seen moving around. However cysts are more commonly found in firm stools. Negative samples don’t always rule out giardia, and several stool samples should be studied over a one week period before a definite diagnosis is made.
ELIZA – Another method of testing is ELIZA, which stands for (Enzyme-linked immuno sorbent assay). This test detects giardia proteins. This is the more expensive method of testing but has an accuracy rate of around 90% and results are much quicker to obtain.
How is giardiasis treated?
The mainstay of treatment for giardia is Metronidazole (trade name Flagyl). Furazolidone is another antibiotic that can be used to treat giardia.
Metronidazole (trade name Flagyl) is an antibiotic used to treat giardiasis.
Furazolidone is another antibiotic which is used to treat protozoal infections too.
Fenbendazole which is a drug used to control certain wormsÂ is another drug which may be prescribed to treat giardiasis. This seems to be a more popular treatment option of late due to the greater treatment rates compared to metronidazole.
Repeated testing of fecal samples are required before your dog can be declared free of the parasite.
Cysts are able to stick to the coat of your dog and he should be bathed several times during the course of treatment.
Environmental decontamination using a bleach solution of 1:30 can be used to disinfect affected areas.
Can I catch giardiasis from my dog?
The jury is still out on this. So it is safest to err on the side of caution and assume you can. Strict hygiene should be practiced.