A single-cell parasite that can cause diarrhea and other challenges Giardiasis is when an animal (human or otherwise) has an intestinal infection of a protozoan (single-celled organism) parasite known as Giardia duodenalis (often referred to as Giardia). Giardia duodenalis has seven different genotypes, each of which tend to affect different species at different frequencies. Dogs are the most common hosts for Giardia duodenalis genotypes C and D. Giardia is a common cause of diarrhea and other illnesses, but many dogs with giardia have no physical signs at all. Dogs can easily become infected after ingesting giardia cysts. This could occur by drinking contaminated water, eating contaminated grass or plants, coming into contact with another animal’s feces, or licking their own body after rolling in contaminated dirt. Once ingested, the cysts transform into their trophozoite, or feeding form, which attaches to the walls of the intestines. The trophozoites reproduce, growing in number, then transform into cysts that are shed through the feces so the cycle of infection can continue. These cysts are immediately infectious to other animals. The cycle from ingestion to shedding generally takes 5-12 days. Giardia cysts are hardy and can live in the environment for weeks or months. Signs of giardia infection in your dogThe most common sign of giardia is diarrhea that is very foul-smelling, sometimes containing mucus or blood. The diarrhea can be intermittent. Some dogs will be less active, may lose weight, or will vomit. For puppies and dogs with compromised immune systems, giardia can be deadly. But some dogs will have no signs of giardia infection at all, instead being asymptomatic carriers. Diagnosis of giardiasisGiardiasis can be tricky to diagnose; giardia does not always show up on a standard fecal test and cysts may be shed intermittently. To test your dog for giardiasis, you will need to present a fresh (less than day old) stool sample. You can get a container from your veterinary clinic or carefully place the stool in a clean resealable plastic bag, storing it in your refrigerator for up to 24 hours. Your veterinarian may start with a fecal exam (a “fecal float”) under the microscope. They mix the feces with a solution that allows the cysts to float to the top of the sample. Unfortunately, a failure to observe giardia cysts in a fecal float does not mean the dog is all clear. An ELISA (enzyme-linked immunoassay) test is, in most cases, the most accurate way to detect giardia by detecting the presence of antigens (foreign proteins) in the stool. It’s often used to confirm suspected cases of giardia infection. Some veterinary clinics can perform this test in-house, whereas others may have to send the sample to a laboratory for testing. Because of the elusive nature of the giardia cysts, your dog may need multiple tests, especially if symptoms persist. Your veterinarian may also want to retest your dog after treatment to ensure treatment was successful. A positive test confirms the presence of giardia, but not all dogs who test positive will require treatment. Prognosis for dogs with giardiaFor most dogs, the prognosis for giardiasis is good. Geriatric dogs and dogs with compromised immune systems are at greatest risk of complications and death. The most common medications used to treat giardia infection are fenbendazole (also known as Panacur® and Safe-Guard®) and metronidazole (commonly known as Flagyl). In some cases, combination therapy with the two medications may be recommended, especially if giardiasis persists. There are other medications that are sometimes prescribed for giardia, so the best approach is to discuss your dog’s health with your veterinarian to come up with an appropriate treatment plan. Treatment typically ranges from 3 to 10 days, with a retest following completion of treatment. Some dogs will also need supportive care for the diarrhea such as subcutaneous fluids or other drugs. Some dogs may do well on a highly digestible diet to firm up the stools during giardia treatment. Healthy dogs with a positive giardia test may or may not need treatment, depending on their health, other animals in the home, and the health of the humans they live with. Because dogs can get re-infected, and can infect other animals (including humans), it is critical to thoroughly treat the environment. Dog feces must be cleaned up and carefully disposed of immediately after your dog has a bowel movement. Regular bathing of your dog’s coat can prevent cysts from getting stuck in their fur. The environment must be disinfected routinely. A dilution of chlorine bleach (1:32 or 1:16) can be used on surfaces that are appropriate for bleaching (e.g., hard, non-porous surfaces such as glass and tile). Steam cleaning may also be helpful. All pet bedding should be laundered regularly. All toys, food and water bowls, and dog crates should also be cleaned frequently. Outdoor Environment Giardia can survive for months in outdoor environments. To limit exposure and re-infection:
Remove dog feces from your yard regularly
Use caution when allowing your dog in outdoor spaces where other dogs may visit, such as dog parks and hiking trails
Do not leave standing water in your yard
Bleach and disinfectants are generally not effective in treating outdoor areas, especially grass or dirt
ZoonosisGiardiasis is a zoonotic condition, meaning that it is infectious between species. Humans are more likely to be infected by a different giardia genotype (A or B) than dogs (C or D), so the risk of getting giardia from your dog is low. However, it is recommended to practice good personal hygiene when handling dog feces, especially for dog owners who have immunodeficiencies. If your dog does have giardia, then environmental disinfection is going to reduce the risks of human infection, infection to other animals, and re-infection in your dog.