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Pets & Parasites: Part 3

Coccidia & Giardia are invasive, non-worm parasites that live in a dog's intestinal tract. What makes them particularly dangerous is that they can infect a dog before they actually appear sick. It may not be clear that the dog is carrying these parasites until stress or another immunity-compromising factor arises.


Coccidia is single-celled and found more frequently in puppies, where they may acquire it through their littermates or mother. Older dogs and cats may also be susceptible.


Giardia is found throughout the U.S. and is, unfortunately, a pervasive protozoan. Transmission of these parasites can come from infected soil, water, feces, food, other animals, and more. As with all parasites, diligent sanitation practices are important to stave off these parasites.


Coccidiosis typically refers to gastrointestinal infections with Isospora species of coccidia. At least four different genera of coccidia can infect dogs: Isospora canis, I. ohioensis, I. neorivolta, and I. burrowsi.


These microscopic parasites spend part of their life cycle in the lining cells of the intestine. Despite damaging these cells, most infections in dogs are not associated with any detectable clinical signs. Infections without clinical signs are called sub-clinical infections. The species that most commonly cause clinical infections in dogs is I. canis, but Cryptosporidium parvum (another coccidian parasite) can as well, especially in puppies.


How did my dog become infected with coccidia?

A dog most likely became infected with coccidia from swallowing oocysts (immature coccidia) that are found in dog feces and soil contaminated with feces. Infected dogs pass oocysts in the feces. These oocysts are very resistant to a wide variety of environmental conditions and can survive for some time on the ground. Under the right conditions of temperature and humidity, these oocysts sporulate or become infective. If a susceptible dog ingests the sporulated oocysts, the oocysts will release sporozoites that invade the intestinal lining cells and set up a cycle of infection in neighboring cells. Dogs may also become infected indirectly by eating a mouse that is infected with coccidia.


What kinds of problems are caused by coccidiosis?

The most common clinical sign of coccidiosis is diarrhea, but most dogs that are infected with coccidia do not have any clinical signs. When the coccidial oocysts are found in the stool of a dog without diarrhea, they are generally considered a transient, insignificant finding.


However, in puppies and debilitated adult dogs, coccidiosis may cause severe watery diarrhea, dehydration, abdominal distress, and vomiting. In severe cases, death may occur.


How is coccidiosis diagnosed?

Coccidiosis is usually diagnosed by performing a fecal flotation test to look for oocysts under the microscope. Since the oocysts are much smaller than the eggs of intestinal worms, a careful evaluation must be made. Detection is made easier when a zinc sulfate flotation solution is used. Infection with some of the less common coccidial parasites may be diagnosed with a blood test.


How is coccidiosis treated?

Your veterinarian may prescribe a sulfa-type antibiotic called sulfadimethoxine, which is usually given for 5-25 days. In severe infections, it may be necessary to repeat the treatment. If the diarrhea is severe and your dog is dehydrated, other medications and treatments, such as IV fluids, may be required. If the sulfa-type antibiotic is not effective at clearing the infection, other treatments are available; your veterinarian will discuss these treatments with you. Some dogs may not require much in terms of medical treatment, depending on the severity of the condition. Reinfection of susceptible dogs is common so environmental disinfection is important. The oocysts are very resistant to environmental conditions and disinfectants. The use of diluted chlorine bleach [one cup (250 ml) of bleach mixed in one gallon (3.8 L) of water] is effective if the surfaces and premises can be safely treated with it. Be sure to test clean a small area of any affected materials since bleach can damage many surfaces. Steam cleaning may also be used to destroy oocysts. Be sure to remove any feces as quickly as possible from the environment to prevent reinfection.


Can the coccidial parasites that my dog has infect me or my family?

The most common species of coccidia in dogs do not have any effect on humans. However, less common species of coccidia can potentially infect humans. One species, called Cryptosporidium, may be transmitted to people. This parasite, which may be carried by dogs and cats, has also been found in the public water supply of some major cities. It poses a health risk for those who are immunosuppressed, such as people with HIV, people taking immune-suppressing drugs, cancer patients, and the elderly.


Good hygiene and proper disposal of dog feces are important in minimizing the risk of transmission of all canine parasites to humans or other animals.







Giardia is a simple one-celled parasitic species; it is not a "worm", bacteria, or virus. There are seven genotypes, A through G, with dogs being most commonly infected by C and D, cats with F, and humans most commonly infected with A and B. Genotype E and F are rarely reported. The parasite occurs worldwide and is a common cause of "Traveler's Diarrhea" in people. Outdoor enthusiasts who inadvertently consume contaminated water may develop "beaver fever", which is another name for giardiasis in people. Other examples of protozoan parasites that can cause intestinal disease are Coccidia, Cryptosporidia, and Toxoplasma. Giardiasis can be an important cause of illness, especially diarrhea, in animals and people. However, the majority of dogs infected with Giardia do not have diarrhea, vomiting, or any other signs of illness. The Giardia organism has two forms. A fragile feeding form, known as the trophozoite, exists in the gut of infected animals, while a hardy cystic form is shed in feces and can survive several months in the environment, particularly in water and damp environments.


How do dogs get giardiasis?

A dog becomes infected with Giardia when it swallows the cyst stage of the parasite. In susceptible dogs, once the cyst passes into the dog's intestines, it goes through a transformation to the trophozoite, or feeding form, and attaches to the intestinal wall to feed. If sufficient numbers are present, clinical signs of damage to the intestinal wall will develop.


Trophozoites reproduce by dividing, and some transform into cystic forms. Eventually, the dog passes infectious cysts in its stool. The time it takes from ingestion of cysts to passage in feces is 5 to 12 days in dogs and 5 to 16 days in cats. These cysts are immediately able to infect another animal. Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground, or by drinking contaminated water.

When Giardia cysts are found in the stool of a healthy adult dog without diarrhea, they are generally considered a transient, insignificant finding. However, in puppies and debilitated adult dogs, they may cause severe, watery diarrhea that may be fatal if left untreated. The likelihood of developing disease increases when large numbers of cysts are present in the environment from fecal contamination. Giardiasis is a common occurrence in environments that are densely populated, such as kennels, pet stores, or animal shelters.


What are the clinical signs of giardiasis?

These microscopic parasites attach themselves to the intestinal wall and the damage causes an acute, sudden-onset of foul-smelling diarrhea. Giardia infection in dogs may lead to weight loss, chronic intermittent diarrhea, and fatty stool. The stool may range from soft to watery, often has a greenish tinge to it, and occasionally contains blood. Infected dogs tend to have excess mucus in the feces. Vomiting may occur in some cases. The signs may persist for several weeks and gradual weight loss may become apparent. Diarrhea may be intermittent. Most dogs do not have a fever but may be less active. The disease is not usually life-threatening unless the dog’s immune system is immature or immunocompromised. Many dogs will be asymptomatic carriers, never developing any signs of illness. Younger animals are more likely to exhibit clinical signs.


How is giardiasis diagnosed?

A routine fecal flotation test may fail to detect these tiny cysts, which are shed inconsistently in the feces, and which often require a special zinc sulfate flotation solution for detection. Occasionally, the parasites may be seen on a direct smear of the feces. If your veterinarian suspects giardiasis, a sample of stool may be analyzed for the presence of Giardia-specific antigens (cell proteins). Some Giardia tests are available for in-clinic use while other tests require submittal to a reference laboratory. Many cases are presumptively diagnosed on the basis of medical history and clinical signs suggestive of giardiasis.


How is giardiasis treated?

The most common drugs used to kill Giardia are fenbendazole and metronidazole. These drugs are normally given for three to ten days to treat giardiasis. Both drugs may be given in combination if necessary. This combination is usually administered to dogs with refractory diarrhea (diarrhea that hasn't responded to treatment). Supportive treatment with other drugs may be needed as supplemental therapy if dehydration or severe diarrhea is present. A low-residue, highly digestible diet may help lessen loose stools during treatment. Some dogs may require follow-up tests and treatments based on their condition and severity of infection. All infected pets should be re-tested two to four weeks after completion of treatment. Dr.McMillen will help determine what course of treatment is best for your pet. Because Giardia cysts are infective immediately when passed into the environment, feces should be removed quickly and disposed of. Infected animals should be bathed regularly to remove cysts from the hair coat.


What is the prognosis for giardiasis?

The prognosis is good in most cases. Debilitated or geriatric animals and those with incompetent immune systems are at increased risk for complications, including death. All pets diagnosed with Giardia should be re-tested two to four weeks after completion of treatment.


Can my dog give a Giardia infection to me or my family?

Giardia can cause diarrhea in humans and can potentially be passed from dogs to humans. In the past, it was assumed that cats and dogs, along with wildlife, were an important source of infection for humans. Genotype A can infect humans, dogs, and cats while B can infect both humans and dogs. However, human-to-human transmission is also important and contaminated municipal water supplies are responsible for many outbreaks. If your dog is diagnosed with giardiasis, environmental disinfection and good personal hygiene are important to prevent accidental spread to humans. In particular, people with immunodeficiency, such as cancer, or who are undergoing chemotherapy, should use extreme care, especially when handling feces or after administering medications.


For environmental disinfection, you can use chlorine bleach at 1:32 or 1:16 dilutions, or 1-2 cups in a gallon of water. Quaternary ammonium compounds (Parvosol®, etc.) are also reported to be effective in killing cysts. Giardia cysts are susceptible to drying so try to keep your environment as dry as possible. For best results, thoroughly clean the pet's living and sleeping areas and then allow the areas to dry out for several days before reintroducing pets.






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