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Internal Parasites


The thought of some worm-like creature living inside our pets or us, for that matter, is unsettling.  Distain aside, internal parasites have a pretty cushy life.  They live in a warm place, food is available whenever they want it, and someone else does the work to supply it.  You might say that parasites are evolution’s original gold-digger.  Not bad work, if you can get it.

A parasite is an organism that lives off another organism (the host) and derives nutrition, usually at the host’s expense.  While the parasite exists at the expense of the host, it is in the parasite’s best interest not to be too detrimental to the host.  If the host dies, then the parasite dies.  As a rule, most intestinal parasites tend to be a nuisance rather than a major cause of illness.  That said, there are cases of puppies and kittens being so heavily parasitized that they became severely debilitated and died.  Another concern with some intestinal parasites is that they can potentially infect people (zoonotic disease).  The two most common parasites that do this are roundworms and hookworms.  Human infection caused by these two parasites is not due to direct transmission from the pet to the owner, but is due to indigestion of or contact with contaminated soil.  Zoonotic disease is not common and is usually prevented by good, routine hygiene.

Most intestinal parasites are contracted by ingestion of larvated eggs or by free living larva on the grass or in the soil.  Since dogs and cats tend to explore the world with their noses, it’s easy for them to pick up these intestinal “livestock”.  Some intestinal parasites can also pass through the placenta (trans placental migration) to infect the young before birth.  In contrast, tapeworms need to develop in another host (an intermediate host) before they can infect a cat or dog.  This intermediate host is usually a flea or a rodent.  When a tapeworm intermediate host is accidentally swallowed or eaten, they can then develop into a segmented adult worm.

Unless heavily parasitized, most pets have mild to moderate illness associated with intestinal parasites.  They include nausea, vomiting, diarrhea and an unkempt, potbellied appearance.  One exception to this is coccidia, a protozoal parasite.  A coccidia infection in a puppy can be severe enough to look like a life-threatening case of parvovirus.

Most intestinal parasites are diagnosed with a fecal flotation examination by your veterinarian.  Tapeworms are an exception to this since their eggs are not commonly found in a fecal float.  The diagnosis is made by seeing short, mobile segments or dried, rice like segments around the hind end.  Treatment protocols are based upon the parasite that is found.

Prevention is an important part of control.  Parasites can be prevented by adopting the following guidelines:

  • Annual fecal exams for all pets:  Identifying internal parasites in one pet and treating it can help prevent parasites in your other pets
  • Treat parasites a soon as they are diagnosed:  Early treatment will help prevent illness in your pet and will also help prevent environmental contamination.  For example, larvated roundworm eggs can persist for years and are nearly impossible to eliminate from contaminated soil.
  • Pick up stool daily:  During hot, humid weather some parasite eggs can become infective within 1 to 3 days.  Proper and prompt cleanup will help prevent soil contamination and reinfection.
  • Keep dogs on a heartworm preventative that helps to control intestinal parasites.
  • Routinely deworm puppies and kittens:  Follow your veterinarian’s recommendations for routine deworming since many puppies and kittens will have adult worms before eggs can be found in their stool.
  • Routinely deworm cats:  For cats that hunt, consider routinely deworming them for tapeworms 2 to 3 times a year since these worms are not routinely found on a fecal exam.
  • Cover sandboxes and play areas to keep children safe by preventing other animals, especially cats, from using it as a litter box.

More information on specific intestinal parasites can be found at the Companion Animal Parasite Council website at