Chris Kouwenhoven

Parasites in our pets

Today we will begin a series on the more commonly seen parasites of dogs and cats. One of the most frequent questions that most any small animal veterinarian hears concerns parasites.

Basically, there are two types of parasites we find in all animals. The first, ectoparasites, are found on the outside of the skin. The ectoparasites you are likely most familiar with are fleas and ticks. Unless the pet is in extremely poor condition, is very young or old, or is suffering from other illness, ectoparasites by themselves are generally not life-threatening. Massive infestations of either ticks or fleas may result in sufficient blood loss to create anemia and death, but this is most unusual in pets.

***Fleas: Flea infestation has become reasonably easy to control in the last few years, since the advent of the drugs that interfere with the life cycle of the fleas. As most of you will remember, flea dips, collars, and sprays were only very temporary measures directed at killing the flea on and around the animal. Naturally, as soon as Kitty or Fido went outside again, new fleas soon found a new home. Control of flea infestations is important, not only for the comfort of your pet, but for yours as well. Having to have a house, especially with carpets, professionally fumigated because of an infestation of fleas, is an experience you don't want to repeat.

Another important reason for control of fleas is that an allergy to flea saliva frequently develops in cats, dogs and people. Flea bite allergy may result in severe itching and dermatitis with extensive damage to the skin, often followed by a secondary bacterial infection. Additionally, there are some very dangerous infectious agents transmitted by fleas and other internal parasites use the flea as a means of transmission to a new host.

Although there are a number of fleas commonly found, by far the most frequent is the cat flea (Ctenocephalides felis), followed by the dog flea (C. canis). The cat flea is responsible for the most severe allergies in cats, dogs and humans.

***Ticks: The other major ectoparasite seen in dogs and cats is the tick. Ticks are responsible for the transmission of a number of serious diseases in both pets and people. Dips, dusts and sprays are the most commonly used eradication methods. Most control programs are designed to reduce the free living stage of the tick in the environment. For most people and pets, ticks are less of a problem than fleas.

On a personal level, our family has a dog and nine cats, all outdoors (we live on a farm) and since I began using the flea control programs that interfere with the flea's life cycle, our animals have been completely flea free (try saying that five times quickly!). Two of the cats come in the house regularly and we have not had a single flea in the house since initiating this treatment over two years ago. Talk to your pet's veterinarian about starting this treatment if you haven't already.

We will be continuing the series on parasites that we started Since this is a rather large topic to cover, it will be ongoing for some time. Perhaps we will not run the series continuously, but rather cover other topics, and come back to the parasite series from time to time until it is completed. As I mentioned last week, it is a topic that generates lots of questions to practicing veterinarians, but I don't want to bore our readers, either.

Last time we discussed external parasites (ectoparasites) and in the next part in this series we'll start with some of the internal parasites (endoparasites). Unlike the ectoparasites, the internal ones come in a great variety and involve a wide variety of organs and systems. Before we get down to the individual types, I'd like to discuss the whole concept of parasites with you.

Parasites form a relationship with a host organism in which the host provides something, usually nutrition, that the parasite can not obtain on its own. In a true host-parasite relationship, only one of the pair, the parasite, benefits from the relationship. Since the parasite is dependent on the host for life, it is critical for the parasite not to cause enough host damage to cause death of the host. Ectoparasites can easily leave a dying or dead host, but internal ones generally can not, and they die with the host. So, in nature, a successful parasite is one that can live in the host without causing permanent damage to the host. Another important part of this relationship for the parasite is the need to reproduce, either within or outside of the host, and for the next generation of the parasite to infect another host. If this infection of new hosts did not occur, the parasite would die when the host died of old age.

It is this need to reproduce itself and to infect new hosts that help us to diagnose internal parasitic infections in people and in our pets. Usually the parasite produces eggs and the detection of these eggs, often in feces, is what enables us to diagnose and treat parasitic infections. Since each of these parasite eggs have individual characteristics that enable us to tell one type from another, your veterinarian is able, after a microscopic examination, to treat parasitic infections with specific drugs, rather than taking a "shotgun" approach to treatment. Not only is this much safer for your pet and generally less expensive for you, but it also decreases the chance of the development of resistance by parasites to the drugs we use to treat the infections.

The most common method for detecting parasite eggs in the feces is the fecal floatation test. Since the parasite eggs are less dense than most of the rest of the fecal material, they will float to the surface of the solution that is mixed with a sample of feces. To aid this tendency for the eggs to float, a saturated solution is used. This simply means that a quantity of sugar or similar material is mixed with the water to increase the difference in density between the floatation solution and the parasite eggs. This is exactly why it is easier for you to float in the salt water of the ocean than it is to float in a fresh water lake or pool. The eggs are collected on a microscope slide and examined by either the veterinarian or a trained technician to make the diagnosis and dispense the appropriate medication.

We will continue our series on the parasites commonly seen in dogs and cats. Previously we discussed external parasites (ectoparasites), such as fleas and ticks. While there are other ectoparasites that occur in our pets, they are not common. Perhaps in the future we will return to them.

There are many more types of internal parasites (endoparasites) than ectoparasites. The most common system involved is the gastrointestinal tract; however, many other systems may be affected by their own specific parasites. We may find parasites in the blood, lungs, muscles, liver and other organs and tissues.

Earlier in our series we defined the ideal parasite-host relationship in some detail. For those of you that may have missed that issue, let me summarize that relationship by the phrase "do no serious damage". It is important to the endoparasite that the host continue to thrive, for if the host should die, the parasites die with it. This relationship is probably best illustrated by the parasites of the gastrointestinal tract.

Roundworms (Ascariasis)

Probably the most common intestinal worms seen, especially in kittens and puppies. There are three major species seen: Toxocara canis, T. leonina and T. cati. Of the three, T. canis is the one we are most concerned about. Massive infections can be fatal to puppies, but occur less often in kittens. Additionally, humans may become infected with T. canis larvae, sometimes resulting in some rather serious pathology. Toxocara canis can be dangerous to humans because it is not a natural parasite in people and, rather than establish the normal host-parasite relationship in the intestinal tract, it wanders through other body organs, thereby causing sometimes significant damage. As you might expect, young children, who sometimes have questionable hygiene, are at greatest risk. Parents can virtually eliminate the risk by ensuring that the family dog is properly tested and, if necessary, treated to remove these potentially dangerous parasites. Thorough cleaning of the areas where puppies defecate will also aid in reducing the potential risk of children ingesting the resistant eggs from the environment. Both the testing and treatment are inexpensive and should be accomplished during routine vaccination visits to your family veterinarian.

The reason T. canis is so common in puppies is that it is transmitted to the unborn pups through the placenta and also through the milk to nursing puppies. Young animals so infected will generally exhibit a failure to grow, often have a dull haircoat and have that "potbellied" look that many people correctly associate with an infestation of intestinal worms. Frequently, worms will be vomited up or appear in the feces, with or without diarrhea. Since the larva migrate through the lungs, coughing and respiratory distress may be seen, but less seldom than the gastrointestinal symptoms.

Toxocara. leonina is not transmitted prenatally but may be transmitted through the milk. T. cati is not transmitted by either route to the puppies. Adult animals may be infected with any of the three, but T. canis is the most commonly seen.

This issue might seem scary to you, especially those of you with young children, but please don't let it alarm you. What I am trying to do is to inform you of the potential dangers so that you can take steps to insure the health of both your children and your pets. Pets and people are a wonderful combination.

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