Does your dog often suffer from diarrhoea, perhaps to the point that it is unable to control where and when it does its business? Does your dog suffer from smelly flatulence and a grumbling belly? If the answer is yes, especially if your dog still eats with gusto and appears to be generally well, the culprit may be giardia, says Dr Lloyd Kenda of Valley Veterinary Centre

"Giardia is an internal parasite, a protozoa, that can live in the small intestine of dogs, cats, people and many other animals. It is found throughout the world and commonly encountered in Hong Kong," Kenda says.

He adds that while it is generally believed that infection with giardia is quite common, clinical signs of infection, giardiasis, are not so common.

Kenda explains that animals, such as a dog, can become infected with giardia by ingesting the cyst form of the parasite, passed on via the faeces of an infected animal. Once in the small intestine, the cyst hatches and releases an active form called a trophozoite. These have hair-like structures (flagella) that whip back and forth allowing them to move in the intestines, where they attach to the intestinal wall and divide in two. After many divisions the bug develops a wall around itself, becoming a cyst which is passed into the environment via the faeces, the vet says.

"The giardia in the faeces can contaminate the environment and water going on to infect other animals and people."

So what are the common signs of infection? Kenda says that most infections are asymptomatic. However, if disease does occur, it is usually presented as diarrhoea. Kenda says that "there is also often a lot of flatulence which, combined with the very watery diarrhoea, can result in an urgent need for the dog to get out and poo, or often not be able to make it outside in time."

Most dogs, and cats, with giardiasis are still quite bright and active, adds the vet; rarely will they vomit, and most retain a good appetite. The diarrhoea, however, will generally be watery, with a particularly bad smell and often appears a little greasy.

For those reasons, giardiasis can be difficult to diagnose because the protozoa are so small and are not necessarily passed with every stool. In severe cases, though, the active protozoa can be seen under the microscope.

"Antigen-based tests can now be used to help diagnose the presence of giardia, and these tests are accurate and helpful to rule in or out giardia as a possible cause of chronic diarrhoea in pets."

Kenda says that a positive test does not necessarily mean the animal has giardiasis.

"Giardia can be found in many animals with and without diarrhoea. If giardia is found in a dog with diarrhoea it may just be a coincidence and not necessarily the cause of the diarrhoea."

If a pet does have continuing diarrhoea, it is important to take it to a vet regardless of the cause.

"If we suspect infection with giardia, and even if we cannot find the protozoa in faecal testing, we will often treat for it anyway," Kenda says.

There are medications available to use to treat for giardia, and some of these can kill bacteria that could also cause diarrhoea.

"So if the diarrhoea was caused by bacteria, and not giardia, the bacteria can be killed and the symptoms eliminated."

There are some measures owners can take to prevent their pet from suffering from giardia, Kenda says. The cysts can live for months outside the host in wet, cold environments, the vet says, so parks, kennels, pet shops and other areas that may be contaminated with animal faeces can be a source of infection.

Drinking water can be another source of infection. Kenda says, "Even tap water in your home can be a potential source. Hence it is recommended to drink only boiled tap water, for both you and your pets. Remember filtering or freezing the water does not get rid of giardia." 

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