Giardia is a parasitic infection caused by a microscopic organism. Many different strains exist, and it can affect many species, including humans. The main symptom associated with Giardia infection, or giardiasis, is diarrhea. Infection can be difficult to diagnose, although treatment is usually curative.

Infection with Giardia occurs when contaminated feces is ingested, or when infectious Giardia cysts are ingested in contaminated food or water. Giardia is commonly found in moist environments such as muddy soil and ponds. It is more common where large numbers of pets are housed in close quarters. Dogs are more commonly affected than cats.

Most types of Giardia have a preference for a particular host species. Some types are transmissible from pets to humans. However, cases of human Giardia that have been transmitted by pets have been poorly documented, and are more frequently a result of direct exposure to infected human feces (i.e. changing diapers) or environmental exposure.

Although some question remains regarding the potential for transmission between species, it is known that Giardia from certain animals will not infect others. For example, the type of Giardia that affects birds does not cause active infection in dogs. 

I am often asked if dogs can get giardia from eating bird or duck feces. The simple answer is no.  The types of Giardia that affect birds may be ingested by dogs, but they pass through the GI tract unchanged; therefore, cysts from bird feces may be seen on a dog’s fecal examination, but the organism does not cause active infection.

Giardia can be difficult to diagnose because it is not usually visible on routine fecal examination.  It is sometimes visible on a type of fecal examination known as a direct smear, however this method is not very reliable. Certain types of giardia which are not infectious to pets, such as the type that infects birds, may show up on fecal examinations, although they do not cause illness.

A laboratory test for Giardia is available. However, the organism is not consistently shed by infected dogs. It can also take five days to two weeks after infection for the test to show up as positive, although diarrhea may develop earlier. Therefore, repeat testing may be necessary to identify infection.

To further complicate matters, many healthy pets normally have a small amount of Giardia in their GI tract. Although opinions vary on whether to treat asymptomatic carriers, pets that have Giardia in their feces without showing signs of infection are usually not treated.

If a pet with diarrhea is diagnosed with giardiasis, he or she will usually be treated with oral medications. Frequent bathing is also recommended, since the infectious cysts can stick to their fur.  Giardia rarely causes serious disease, so supportive care is rarely necessary. Pets that are suffering from dehydration secondary to diarrhea may require fluid therapy. Pets with severe symptoms from Giardia usually have an underlying health problem, so severely affected pets may require further diagnostics to identify concurrent diseases.

Dr. Kelly Sulik owns and operates Animobile Mobile Veterinary Services in Tryon, N.C. She can be reached at animobiledvm@gmail.com.