Intestinal Parasite Q & A

By: Dr. Shannon Smith

The staff and doctors at Bothell Pet Hospital are frequently asked questions regarding intestinal parasites and various fecal tests.  Here are a few commonly asked questions and their answers:

Q:  Why should I do an annual fecal intestinal parasite screen on my pet? 

A:  Nearly all puppies are born with roundworms and kittens become infected shortly after birth, most often via nursing.  Since almost all puppies and kittens have roundworms, they will need to be treated.  We recommend testing young animals to be sure all of the roundworms are gone and no further treatment is needed, and to be sure they are not infected with any other parasites that may require a different treatment.

Eggs of intestinal parasites and some one-celled organisms are microscopic and can be found anywhere outdoors.  Our pets can become infected by ingesting these eggs, either directly, such as by eating grass or animal stool, or indirectly, such as by licking them off of their paws or fur while grooming.  Some parasites, like Giardia, can be ingested by drinking from contaminated water sources.  A periodic check of a stool sample will help us then be sure we’re catching new infections.

Another reason we should be checking stool samples for parasites annually, at a minimum, is that some parasites can be transmitted to humans.  (Zoonoses is the term that refers to a disease that can be transmitted from animals to people.). According to the CDC, 14% of people in the United States have been infected with roundworms!  Is your mind now wandering to puppies that have licked your face or to children playing in the grass or dirt and putting their hands in their mouths?  Yes, we can become infected with parasites from our pets!  We need to keep our pets free of parasites to prevent transmission to people.

Q:  Why can’t I give a dewormer instead of testing for parasites?

A:  There are several different intestinal parasites that infect dogs and cats.  Because each parasite has a different lifecycle and may require a different medication for treatment, we need to identify the parasite in order to effectively eliminate it. Additionally, some parasites require follow-up testing or treatments, or environmental decontamination and precautions. For example, tapeworms, infecting dogs and cats, may be a species that come from ingesting fleas during grooming or a different species that is acquired by eating rodents.  If the tapeworm is the species from fleas, then we know that flea treatment will also be needed to control the infection.

Q:  If my dog has diarrhea, can I just drop off a stool sample for testing? 

A:  We may need to assess the overall status of your pet. A few diseases that cause diarrhea can be diagnosed via fecal testing, but most cannot.  Most cases of diarrhea are fairly benign and easily treated, but sometimes there can be a very serious underlying disease.  Depending on the age, history, symptoms and duration we may allow a sample to be dropped off for screening, but it is more likely that an exam will be needed in order to decide which tests are most appropriate for your pet.

Q:  Why did my cat/dog’s fecal intestinal parasite screen come back negative for parasites when I saw tapeworm segments in the stool? 

A:  Tapeworms are long worms made up of many small segments. They shed eggs into the environment via these segments. You might notice segments in the stool that may be up to an inch long when fresh or you may see dried segments that look like a flat grain of rice caught in the fur at your pet’s back end.  In order for an egg to show up in a fecal sample, there must be a segment that was in the particular portion of the sample that the lab used and that segment must break open, spilling the eggs into the solution being tested.  So, if you notice tapeworm segments or need help identifying them, please let us know!

Q:  My pet tested negative for intestinal parasites, so why are we doing more testing on the stool sample? 

A:  Eggs of most intestinal parasites are seen on a fecal flotation. This is a test where the stool is mixed with either a sugar or salt water solution and is then centrifuged (spun) to allow the eggs to float to the surface of the mixture.  We can identify the parasites based on the size, shape and general appearance of the egg.  Sometimes on a fecal flotation, the lab will be able to also identify a very tiny one-celled organism, called Giardia, that usually causes diarrhea. However, sometimes Giardia is elusive and requires a more sensitive test specifically designed to detect its presence.

Another frequently used fecal test isn’t actually for an intestinal parasite, but for an intestinal bacteria, called Clostridia.  This bacteria can cause watery diarrhea, intestinal gas and cramping, leading to changes in appetite or vomiting. It may even cause bloody diarrhea. The good news is that this bacteria can be seen on a fecal smear.  Only a very small sample is required for a smear. It is rubbed onto a microscope slide, stained to highlight the bacteria, and viewed under the microscope.

There are many other more specialized fecal tests that may be recommended, including those for lungworms, parvovirus or vitamin and enzyme deficiencies.

Q:  How could my pet test positive for a parasite when the stool looks normal and I see no signs of parasites? 

A:  Here, it is rare to see a puppy or kitten with a large pot-belly that is lethargic, malnourished and anemic due to parasites. Thankfully our clients are very proactive regarding health care for their pets and, while parasites can cause severe illness, we rarely see this in our corner of the world.  Sometimes we will see signs of parasites, such as soft stool or diarrhea, but very often we do not.  Since pets that do not have chronically high parasite burdens may show no signs of infection at all, we should be testing at least annually so we can diagnose and treat these infections before they negatively impact the health of your pet.

Also, some parasites will only shed their eggs intermittently. So, unless they were shedding eggs at the time the stool sample was collected, eggs may not be visible on the test.  Whipworms, for example, can be notoriously difficult to detect due to intermittent shedding and low numbers of eggs.

Sometimes we will also find parasites in the stool that may not affect the pet.  This is sometimes the case with an organism called coccidia. In most healthy adult animals, coccidia can pass through the gastrointestinal tract and the adult will pass them without developing a persistent infection.  In other cases, coccidia from the feces of other animals can be detected in the stool of our pets.  This is frequently seen in dogs that ingest rabbit stool.  Because coccidia is species-specific, meaning it only likes to live in one particular host species, rabbit coccidia will not infect dogs. It will only be seen as it passes through their system without causing disease or infection.

Hopefully, this review will give you a better understanding of fecal parasites and testing.  Remember, if any questions arise, we are always happy to help answer them if you give us a call.  We’ll work together to keep “our” dogs and cats free of intestinal parasites.