Internal Parasites – Part Deux

Internal Parasites – Part Deux


July 17, 2014


From the Desk of Dr. Voorheis


 Who’s up for the sequel about the creepy, crawly parasites that live in our precious pets? Two weeks ago we talked about worms. As a reminder, that was an incomplete discussion as I kept it to the most common worms of the alimentary (gastrointestinal) tract. We talked about big worms and small worms that are visible to the naked eye. The little stinkers we are talking about today are tiny one celled organisms. They might be little, but they are mighty and sometimes their effects are devastating. If I limit the discussion to common culprits, we would be talking about just two organisms. But for you, my avid and loyal readers, I’ll offer two or three more.  

Protozoa (Coccidia)

 Coccidia are one celled organisms that cause disease in animals. There are multiple types of Coccidia; Isospora, Eimeria, Toxoplasma, Cryptosporidium and Neospora. Toxoplasma, Cryptosporidium and Neospora deserve “special topic status”. An entire blog could be devoted to these Coccidia and given how serious it is, I probably will write one. I will confine this discussion to Isospora. There are two types that affect our pets. Isospora canis and felis. They don’t cross over. Cat Coccidia is cat Coccidia and dog Coccidia is dog Coccidia. Eimeria is found in the feces of rabbits and deer, so dogs that eat deer and rabbit poop may be affected. Yet another reason to dissuade the poop eating.  

 Isospora primarily affects puppies and kittens. When found in the stool of an adult dog, it might not even be causing disease. It causes watery to mucoid and sometimes blood tinged diarrhea. It can be a cause of weak puppies and kittens. Infected puppies and kittens will contaminate the environment with oocyts. Occasionally, a puppy or kitten can even be anemic from coccidiosis. How are they diagnosed? A fecal exam is done. I cannot stress the importance of an annual fecal examination enough. It is a crucial tool. Treatment is relatively straight forward. If a puppy or kitten is healthy, we treat as an outpatient. If the animal is dehydrated or otherwise debilitated, fluid and other supportive care is indicated. Sulfa drugs are the treatment of choice. We usually treat for a period of ten to fourteen days. The sulfa drug does not eradicate the Coccidia but inhibits it so that body defense mechanisms can reestablish control.



Protozoa (flagellate)



Giardiasis is caused by a protozoan, Giardia sp. Animals are infected when they ingest cyst shed from infected animals, often via shared water. Giardia live in the small intestine, specifically the duodenum, where they interfere with digestion through unknown mechanisms. The cysts are immediately infective when shed in feces. This is a common disease. It wasn’t always as common as it is now. In our hospital setting, Giardia is the most common intestinal parasite diagnosed, outpacing roundworms. It is more common in young animals and signs vary. In some animals this means acute diarrhea while in others it means intermittent and even transient diarrhea. It also can become a chronic disease and can cause a malabsorption syndrome leading to debilitation. It is transmitted when ingested cysts from contaminated feces are ingested through water, food, environment or fur. Indirect water borne transmission is most common and cool moist conditions favor survival. Lest you think by living in our Southern California desert allows us to escape all of this, let’s think of the microenvironment we create in our backyard.  Sprinklers that go off daily or every other day keep the microenvironment in the grass and shrubbery in your backyard cool and moist. The survival of Giardia cysts in the backyard are no problem either. There is a definite higher risk and higher numbers of Giardia in dogs and cats that come from high density populations such as kennels, pet-shops, catteries and animal shelters. Of course a dog or a cat doesn’t come in with a sign that says “Hi, I’ve got Giardia”. Giardiasis diarrhea can resemble either a large or small bowel diarrhea, it can look like IBD (inflammatory bowel disease) or it can look like maldigestion and malabsorption too. In cats it can be confused with another protozoan, Tritrichomonas fetus.


How do we diagnose it? Again, a fecal exam is our number one tool. Routine fecals can find it, cysts can be found on flotation, direct examination of stool will sometimes yield trophozoites and there is a highly specific ELISA test that uses special techniques to test for the Giardia surface antigen. Sometimes two or three tests in succession will be used to both diagnose the disease and/or confirm it is clear. When we treat Giardia, we treat the animals as out-patients in the vast majority of cases. There are cases where Giardia is so severe and so debilitating that the animals require hospitalization. It is recommended that drug therapy such as metronidazole or fenbendazole be combined with environmental cleaning using quaternary ammonia disinfectants plus bathing of the patient to prevent re-infection. There is a Giardia vaccine available, however many internists do not believe this is an efficacious vaccine.                 


There are some animals that do not clear as puppies or kittens. This may be due to resistance of the organism to the medication being used to treat it. Immunodeficiency or a slow maturing immune system may also make it difficult to eliminate the organism. They continue to shed and test positive for Giardia until their immune systems mature, even after a year of age of more. Re-infection is easy because Giardia cysts are resistant to environmental influences and relatively few are needed to reinfect a dog or person. In addition, and this is not common, there are dogs that have chronic Giardia, that either through re-infection or persistent infection develop chronic signs of bowel disease. Fortunately, this is rare.

 The above two organisms, the Coccidia Isospora, and the protozoa, Giardia are by FAR the most common of the one celled organisms affecting the dog and cat.  There are a few others worth mentioning. Trichomoniasis (caused by Tritrichomonas foetus) is another protozoa of interest. The coccidial organisms, toxoplasma, cryptosporidium, and neospora are also worth mentioning.


Protozoa (flagellate)


 Trichomoniasis in cats is caused by Tritrichomonas foetus. Animals are infected by the fecal oral route. Cats with trichomoniasis have signs of a foul smelling large bowel diarrhea which rarely contains blood or mucus. It is more commonly seen in exotic cat breeds such as  Somalis, Ocicats, Bengals and Abyssinians. This may be due to the fact that these cats are commonly “show cats” and the environment where exposure may take place is cat shows where an individual animal is potentially exposed to many other individuals. The disease is diagnosed by either finding motile trophozoites in fresh stool specimens, fecal culture, or the much more accurate PCR testing. In our practice, testing is limited primarily to PCR testing.

Treatment frequently involves testing the entire cattery and separating infected from non-infected, treating the positives and then retesting. Eventually, a cattery with trichomoniasis can be cleared. Some cats have either resistant strains or cannot clear the organism. These cats eventually clear, but may test positive for one or two years.



Protozoa (Coccidia)


 Toxoplasmosis, is caused by the coccidial organism Toxoplama gondii, and is by far too complex a topic to be covered in this short blog. I think I stated earlier an entire blog could be devoted to Toxoplasmosis. Toxoplasmosis can be acquired transplacentally (across the placenta), ingestion of tissues containing encysted organisms such as when a cat eats a mouse with encysted organisms in its muscle or through ingestion of food or water contaminated by cat feces containing oocysts. And toxoplasmosis does not just affect dogs and cats. Marine mammals such as sea lions and sea otters and others are particularly sensitive to toxoplasmosis. It is felt by most wildlife biologists that the feral cat population has a role in shedding the toxoplasma organism into storm runoff channels where it find its way into the food chain that eventually affects sea lions and sea otters. What can we do? Trap, neuter and release feral cat programs. Do not use flushable litter or if you do use flushable litter, don’t flush it. Dispose of it in a way it ends up in the landfill rather than in our water ways. In kittens, toxoplasmosis can cause signs affecting liver, lung, brain and the eye. In older cats, it can be in the lung, the brain, muscle, liver, pancreas, heart and eye. In dogs, lung CNS and muscle infections predominate. We treat toxoplasmosis using a number of different antibiotics but clindamycin is considered the most effective.                           


Protozoa (Coccidia)


 Neospora caninum is a protozoal parasite that causes neuromuscular disease in dogs. Domestic dogs and coyotes are the definitive hosts. They shed the organism in their stool after ingesting the cysts in the muscle from the intermediate hosts like deer and cattle. Another way they get it is to be infected across the placenta, which can cause infection in puppies or subclinical infection causing encystment in neural and muscular tissue. This is another reason to NOT feed raw foods. The organism can encyst in cattle muscle. Neospora can cause a wide variety of signs from the vague, lethargic and muscle sore dog, to a dog showing severe neurologic and muscular signs. Treatment is available, but sometimes the signs are too severe to be reversed. “C’mon Dr. Voorheis have you diagnosed this disease?” No, I have not. However, I am currently treating a dog with suspicion for this disease. Suspicion does not equal diagnosis. But the disease is pretty devastating. So why risk it by feeding raw meat? Remember my nutrition blog from so many months ago? I think I addressed the problems associated with raw diets in that blog. Add this scenario to that list of reasons not to feed raw food to your animals.


 Well, that’s enough of that.  I hope you’ve all enjoyed your tutoring session on internal parasites. Don’t worry, there won’t be a test!


Until next time………


Dr. Voorheis

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