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September's Topic of the Month: Intestinal Parasites

Intestinal parasites are very common in cats and dogs.  Possible parasites include roundworms, hookworms, whipworms, and tapeworms.  They can also get protozoa such as giardia or coccidia.

Checking for Worms

The majority of the parasites mentioned (roundworms, hookworms, whipworms, coccidia, and giardia) cannot be seen with the naked eye in most cases.  To determine whether there is an infection present, a fecal exam is recommended.  That is looked at under a microscope to determine if there are any parasite eggs present.  Two fecal checks three weeks apart are recommended.  This is because if non-egg producing stages are the only ones present at the first check then the test can be a false negative.  Three weeks allows any immature stages to mature enough to begin laying eggs. 

Tapeworms are generally not seen on fecal exams due to the density of the eggs and how sporadically they are passed.  Most cases of tapeworms are diagnosed by the passing of tapeworm segments (which resemble grains of rice) in the stool.  You may even see the segments in the fur around the rectum or in the bedding.

Giardia is the only mentioned parasite that cannot be diagnosed with a fecal check.  This protozoa lives in the cell walls of the intestinal tract of an infected pet and requires a specialized test.  However, unlike fecals, this is not a test that needs to be done annually.  Instead, the doctor may recommend checking your pet for giardia if they begin exhibiting symptoms.


Roundworms can be passed from mother to offspring – either directly through the placenta during pregnancy or through her milk while nursing.  They can also be contracted through an infestation in the environment.  These parasites burrow through the intestines, liver, and lungs before they reach their final destination, the small intestines.

Roundworms can be a health hazard for humans as well.  They are spread through fecal to oral transmission.  The stool can also contaminate the ground.  The biggest risk is to children as they may play outside in an area that has been contaminated and later put their hands in their mouths.  Handling puppies and kittens does not intrinsically pose a health risk but proper hygiene is obviously recommended.

Clinical Signs May Include: diarrhea, vomiting, stunted growth, lethargy, bloated belly


Hookworms are intestinal parasites that can be passed to you and your family.  Hookworms, like roundworms, are primarily transmitted through the ingestion of infected soil or stool.  However, microscopic larvae may also penetrate the foot.  Hookworms graze from place-to-place in the intestines, leaving bloody holes in their wake.

Clinical Signs May Include: Weight loss, bloody diarrhea, anemia


Tapeworms are intestinal parasite that your pet can contract by swallowing infected fleas.  They are segmented worms that live in the small intestine.  The segments are full of eggs – they will fall off the main body and be excreted in the feces.  The segments are flat and mobile when they are fresh and are often seen in the stool or in fur – after they dry out, they resemble grains of rice.  The passing of these segments are the primary method of diagnosing tapeworms.  Flea larvae will ingest the eggs and, once the flea matures, the eggs mature into the infective form.  The infected flea can then be ingested during self-grooming and infect the animal.

Clinical Signs: Primarily the passing of segments, which may cause them to scoot their rectum on the floor; severe cases can cause vomiting


Whipworms are the least common intestinal parasites but the most difficult to eradicate.  However, the prevalence of whipworms has been increasing in the past years.  Most intestinal parasites require two rounds of treatment, 3 weeks apart, in order to clear the infestation.  However, whipworms require 3 rounds of treatment (initial, 3 weeks, and 3 months) in order to clear the infestation.  Additional, it is extremely important to properly clean the environment where an infected animal has been defecating in order to prevent re-infestation.  Whipworm eggs can survive in the environment from anywhere between a few months and a few years.  Severe, untreated whipworm infestations can lead to death.

Clinical Signs May Include: Large-bowel diarrhea, anemia, dehydration, loss of appetite, weight loss


Coccidia is not an intestinal parasite.  Instead it is a single celled organism that can live in the intestinal tract of cats and dogs.  It is more prevalent in younger animals and can cause diarrhea.  Cats can shed a specific type of coccidia called toxoplasma.  It is dangerous to pregnant women and immune-compromised people and is the reason pregnant women should not clean litter boxes.

Clinical Signs: watery diarrhea w/ mucous, severe cases can have bloody diarrhea


Like coccidia, giardia is a single celled organism that can cause diarrhea.  Unlike coccidia, it cannot be observed under a microscope during a routine fecal check but instead requires a specialized test which the doctor may recommend should your pet be experiencing diarrhea.  The most common method of contracting giardia is from drinking contaminated water – which leaves dogs who spend a lot of time outdoors (perhaps hunting or on hikes) especially at risk.

Clinical Signs May Include: Vomiting, diarrhea, weight loss, lethargy


The method of treatment varies based on which parasites your pet has as well as how severe the infestation is.  One thing all of them have in common is that the treatment needs to be repeated in order to completely clear an infestation.  This is because, in most cases, there are six worm life stages and the medications only kill the last three.  Repeating the medication at three weeks is essential to completely killing all of the parasites.  The exception to this is whipworms.  Whipworms need three rounds of treatment – the initial treatment, the three week treatment, and the third is three months after the diagnosis.  This is because the whipworm incubation period is 3 months as opposed to the 3 week average of the other parasites.


You can help prevent your pet from contracting these parasites in several different ways. 

Ensure that fecal matter is removed from your yard – especially if you are introducing a new pet who has not been fully vetted yet. 

Prevent your pet from eating anything off the ground in unfamiliar environments. 

Do not allow your pet to drink from any standing water (puddles, etc.) or outside water sources (lakes, rivers, etc.) – instead always bring a clean source of water with you. 

But the easiest way to prevent the majority of intestinal parasites is monthly heartworm medication.  All heartworm medications also contain a secondary medication to prevent intestinal parasites.  For example, Interceptor contains milbemycin oxime which prevents hookworms, roundworms, and whipworms.  Revolution has selamectin and Heartgard has pyrantel – both prevent hookworms and roundworms.  There are even some preventions available which contain praziquantel which helps prevent tapeworms.