Giardia is a tiny intestinal parasite that can remain dormant in a dog’s system for a considerable period. A dog can become infected with giardia by consuming water in which the giardia cysts are found. Healthy dogs can have giardiasis without suffering the diarrhea that elderly dogs or other debilitated dogs might have. However, giardiasis may be fatal in debilitated or geriatric dogs or dogs with immature or compromised immune systems.
Giardiasis is caused by a single-celled protozoan parasite, called giardia intestinalis. This parasite prefers to live in a cool and moist environment. It is often found in water that has been contaminated with animal feces, where they can live in their cyst form for several weeks or longer outside an animal host.
The giardia protozoans infect their hosts in their immature form. The cyst will mature into a trophozoite once it has traveled to the dog’s intestines, at which time it will attach to the intestinal wall and begin to feed and reproduce. These trophozoites will reproduce repeatedly by cell division, causing increasing damage to the intestinal wall. At some point they will become encysted themselves, being shed in the dog’s feces, to infect another animal.
The damage to the intestinal wall prevents the dog from absorbing the nutrients from his food. This inability to digest his food properly will bring on a foul-smelling, watery or thin diarrhea, which may develop into chronic diarrhea if the giardiasis goes untreated. Diarrhea caused by giardiasis has a variable appearance, possibly appearing pale, greenish, frothy or greasy. It also may have mucus or blood in it.
Risk Factors for Giardiasis
All dogs who live in close proximity to other animals will have contact with giardia cysts. Older dogs, very young puppies and dogs with conditions that weaken their immune systems are at risk of contracting giardiasis. Although dogs can consume cysts by eating feces or food contaminated with feces, they also can consume feces by drinking contaminated water or grooming fur that harbors cysts.
A fecal smear must be done to rule out other causes of the diarrhea when giardiasis is suspected. Confirmed giardia infections are treated with an antibiotic, usually metronidazole for a period of five to seven days, sometimes in combination with the antiparasitic drug, fenbendazole. Dogs exhibiting severe diarrhea may require hydration or other drugs for supportive care. Most dogs with giardiasis are treated by their owners, at home. Treatment can be effective only if the environment is cleaned and disinfected to remove parasitic cysts and preventive measures taken to keep them from being reintroduced. All animals should be shampooed on a regular schedule to keep their bodies free from cysts. Pet owners and caretakers must wash their hands frequently when cleaning up canine feces or handling dogs with giardiasis, whether or not it is known that cysts are present in the environment, as cysts can transferred to human beings.