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Intestinal Parasites


When people talk about worms in dogs and cats they are referring to intestinal parasites, of which there are several kinds. In our climates there are four common kinds of intestinal worms and one protozoan to be concerned about. To be sure, there are others than those we will discuss here, but these are the most commonly found intestinal parasites.

Parasites cause harm to their hosts generally in two ways--by damaging specific organs or tissues, and by robbing the host of vital nutrients. Classic signs that internal parasites have infected your pet include a dull, rough hair coat; a pot-bellied appearance; unthriftiness or poor growth; gastrointestinal disturbances ranging from diarrhea to constipation or vomiting; lack of energy; anemia, and in severe cases, death.

The proper treatment for intestinal parasites requires professional diagnosis of the types of parasites present, selection of a specific safe and effective dewormer, and repeated treatment according to the life cycle of the parasites.

Not all intestinal parasites are visible to the naked eye, so we must begin with laboratory examination of the feces. We do this routinely in all puppies and kittens under our care. When we check a sample we prepare it for microscopic examination by doing a concentration technique which separates any parasite eggs from the fecal debris. Each parasite has a characteristic egg recognizable under a microscope. Checking one sample is about 75% accurate. Checking two is 85% accurate.

Good sanitation practices and disinfection are often necessary to achieve adequate control of bothersome parasites. In addition, controlling fleas and other vermin that can transmit parasites is important for providing the optimum protection for your pet.

Pinworms are unknown in dogs and cats. If your children pick up pinworms, please don't blame the family pet. The life cycle of people pinworms is such that they can only infect other people.

Ascarids or Roundworms

Nearly all puppies are born with large round worms called ascarids. Even though the mother dog may not show signs of ascarid infection, she may have tiny, encysted larvae in her body that are activated during pregnancy and infect the developing fetuses. Ascarid eggs are very resistant to environmental and climactic factors as well as to many chemicals. It is thought that ascarid eggs can stay alive in or on the ground for several years. Puppies and kittens can also become infected by accidentally eating these infective eggs.
Ascarids are very large round worms measuring about 3-4 inches in length, with some growing as large as 6-7 inches long. Ascarids live in the small intestines of puppies and kittens. When you consider how small this organ is in comparison to the large dimension of the parasite, you can see how easily the intestine can be blocked or ruptured when large numbers of ascarids are present.
As the ascarid parasite grows, the immature stages of larvae travel through the pet's liver and lungs, often causing respiratory problems and sometimes death. Active infections of ascarids are less common in adult dogs and cats, presumably because they develop a degree of immunity to the parasite as they grow older.
The treatment and control of ascarids includes the use of safe and effective dewormers which are only effective against adult ascarids and have little or no effect on the migrating larvae. Therefore, it is necessary to retreat the pet at specific intervals as directed by your veterinarian. Good sanitation habits, including picking up and disposing of feces to reduce the potential for reinfection, is important in the control of ascarids.
Pet owners should be aware that ascarids can also cause a potentially serious disease in humans called visceral larval migrans. This disease occurs when children accidentally ingest ascarid eggs when playing in dirt or sand boxes. The eggs hatch into larvae and travel through various organs in the child's body, with the greatest danger being in the brain and optic nerve. While the incidence of this condition is low, its seriousness is quite obvious.


Other commonly occurring parasites in pets are hookworms. Very young puppies can become infected through their mothers' milk while nursing. Dogs and cats of any age may be infected by consuming food or water contaminated with infective larvae, or the larvae can penetrate the animal's skin to establish an infection.
Although animals of all ages can have hookworms, damage is usually more severe in puppies and kittens. Older pets may tolerate the infection without suffering ill effects. Hookworms live in the small intestines where they bite into the intestinal wall, suck blood, and cause the intestine to hemorrhage. In severe cases, the hemorrhage can lead to anemia and in some cases, death. In pets suffering from hookworm infection, the stool is often a dark, tar-like color due to the presence of digested blood.
Treatment for hookworms should be initiated with a dewormer that will remove the parasites quickly and effectively, and be safe for the pet. The treatment should be repeated in 3 weeks. In cases of severe life-threatening anemia, your veterinarian may decide on additional treatment.


Dogs become infected with whipworms by ingesting infective whipworm eggs. The eggs are very hardy, and can remain viable for long periods of time in the environment. Once an area is contaminated with whipworm eggs, dogs using the area are destined to be plagued repeatedly with this parasite. Adult whipworms live in a portion of the dog's intestinal tract called the cecum. Infected dogs are often troubled with bloody, mucus-filled diarrhea, and are usually unthrifty. In many cases, whipworm eggs cannot be found in the watery stool, making it difficult to make a diagnosis. The whipworm parasite is a problem for older dogs, but not for puppies.
Only a few dewormers are safe and highly effective against whipworms. Following initial treatment, the pet should be rechecked in approximately 90 days to determine if another treatment is needed. In many cases, dogs will need to be retreated for whipworms until the dog's habitat has been decontaminated.


This is the parasite most often missed on laboratory examination. It is diagnosed by finding rice-like 1/2 inch segments in the feces, on the hair under the tail, or in the animal's bed. Fresh segments of tapeworm will move like an inchworm--squeeze up stretch out.
Tapeworms have a different life cycle as compared to ascarids, hookworms or whipworms, in that they require an intermediate host or "carrier" for transmission. The flea is the most common intermediate host for dipylidium caninum, while rabbits serve as the intermediate host for taenia pisiformis. To become infected, a dog or cat must ingest a flea or rabbit harboring an infective stage of the tapeworm. Dogs and cats can also become infected by ingesting other contaminated insects or birds and rodents that have either ingested infective insects or have the fleas on them.
Tapeworms can be of gigantic size, several feet long in some cases, and live in the small intestine. Despite their large size, this parasite rarely damages the intestine and the overall well being of the pet is usually not impaired. On occasion, a pet may experience digestive disturbances, but perhaps the most serious problem with the tapeworm parasite is the objectionable sight of tapeworm segments crawling on the pets hind quarters or on the furniture or carpeting.
There are a few modern drugs that are safe and highly effective in the fight against tapeworms. A single treatment is usually all that is needed because tapeworms don't travel through any other part of the dog's or cat's body. Of course, if the intermediate hosts--fleas and rabbits--are not controlled, reinfection is likely to occur.


Coccida are protozoa. They attack the lining of the intestine causing severe digestive upsets. Proper sanitation is a most important factor in coccidiosis control. Coccidia seem to have little effect on adult animals who act as carriers and spread the disease to both young puppies and kittens. Coccidiosis starts with a slight diarrhea which gradually worsens until the feces are full of blood and mucus. The animal then becomes dehydrated and very sick. If left untreated it will soon begin to cough and have a discharge from the eyes and nose and a low grade fever. Occasionally an animal will survive without treatment, but most will start to have convulsions and soon after that, die. Kittens are less seriously affected than puppies. Effective treatment involves daily oral medication for several days.

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