Feline Welfare Society

Most pet owners have had the experience of having their new kittens dewormed by the veterinarian one or more times during their initial visits. But relatively few cats get any sort of follow up deworming over the course of their lives. Some will be treated if the owners witness tapeworm segments on their cat's feces or on their hindquarters, or if the cat vomits up a roundworm on the kitchen floor, but for the most part the only deworming many cats get are the ones done during their kitten visits. The Companion Animal Parasite Council, however, recommends anywhere from 1-4 dewormings per year on cats, depending upon their history and lifestyle. Why the difference? Mostly this is an issue of misinformation and a lack of client education on the subject. Many of you may think, "My cat is indoors only, she never hunts, and her stool sample is always negative for parasites. Why should I deworm my cat?" To answer this question it is important to review the life cycles of some of these parasites, as well to explain what a fecal exam result really means.

Let's start with roundworms. Kittens are primarily infected with roundworms from nursing from their mothers.. The larval worms are actually ingested along with their mother's milk during feedings. Once in the digestive tract, many of these worms begin to migrate through the walls of the intestines and then migrate through the liver and then to the lungs, a pattern called hepatotracheal migration. Once in the lungs these worms are coughed up and then swallowed, all the while furthering their development into adult worms. Once back in the digestive tract these worms will begin producing eggs which will pass with the feces as the cat defacates. Roundworms can also infect cats through oral ingestion of eggs in the environment. These are very hearty eggs that can survive years even in harsh conditions. Mice can also harbor these worms if they ingest the eggs from the environment, which can be passed to the cat if eaten. There is a certain percentage of these worms that will lay dormant in the cat's body tissue and not complete this migration and development pattern. The purpose of these worms are to wait for the hormonal signals that the cat they are in is pregnant. The larval worms then wake from their dormancy and migrate to the mammary glands in order to infect the next generation of kittens. When these worms are in their dormant state they can be somewhat immune to dewormers. In a male cat or a female cat that has been spayed, obviously that hormonal signal never comes. However, many of the dormant larval can still spontaneously awaken and complete the normal hepatotracheal migration, wind up back in the digestive tract and start producing eggs. It is not uncommon to hear of an 8 year old indoor only cat that suddenly vomits up a roundworm.

Now lets talk about fecal exams. This is a procedure which involves mixing a very small amount of stool with a "flotation fluid" which causes eggs present in the feces to rise to the top of the fluid and stick to a coverslip which can then be examined under the microscope. Fecal exams are very important in helping to diagnose existing parasite infections. However it does have its limitations. Think of a fecal sample like a snapshot in time. It is only checking for the presence of eggs in that small quantity of stool. If there were no eggs shed in that moment in time, or if there are no eggs present in that small portion of the stool sample, they can be missed. A negative stool sample does not rule out the presence of parasites.

Lastly, it is important to mention that these worms are potentially infectious to people, especially young children or immunosuppressed individuals. If infected with these worms, various health problems can result, including blindness as the worms can migrate to the eyes. For these reasons, the CAPC has recommended at the very least annual dewormings of all companion pets, regardless of negative stool sample findings. Pets that have a history of hunting, going outside, or have a known history of parasitic infections should have even more frequent dewormings with a broad spectrum dewormer.

Stay tuned for Part 2 of our parasite discussion, in which we will review how cats (and their humans) can be infected with tapeworms.