Internal Parasites in Pets

A guide to help you protect your pet from internal parasites. 

Nice weather generally means your pets face a greater risk of exposure to parasites that could affect their health. 

Read on for a discussion of the most common internal parasites that can present a significant danger to your pet.

Heartworm disease is a serious and potentially fatal disease that can harm both dogs and cats. For the purposes of this article, dogs will be discussed.  It is transmitted by as many as 30 different species of mosquito. 

The life cycle of the heartworm begins when a mosquito bites an infected dog.  The mosquito takes in microfilariae (larvae) when it feeds.   During the next 2-3 weeks, the larvae develop within the mosquito into the infective stage.   When the mosquito feeds again, it can transmit infective larvae to the healthy dog.  If left untreated, heartworm disease can result in death.  If tested positive, treatment is necessary in order to give your dog the best chance at living a full, healthy life.  The most obvious signs of the disease are a soft, dry chronic cough, shortness of breath, weakness, nervousness, weight loss, listlessness, rough hair coat and loss of stamina.

The best way to treat heartworm is to prevent it from happening!  The American Heartworm Society recommends yearly heartworm testing.  If tested negative, dogs should be placed on a monthly preventative.  Most of these drugs also prevent and control some of the intestinal parasites listed below.  This is why it is important to give these medications year round.  The cost of prevention is minimal compared to the expense of treatment. 

Roundworms are spaghetti-like worms are often seen in the vomit and feces of puppies and kittens. They can cause serious problems for all the members of your family, including the humans (usually children). 

Most puppies are born with a roundworm infection, the most common intestinal parasite affecting dogs.  Kittens are more likely to be affected than adult cats.  Outdoor cats are more likely to become infected with roundworms than indoor cats, especially if they hunt.   Dogs and cats can develop adult worm infections within the digestive tract. Other possible modes of roundworm infection include either ingestion of infective eggs from the environment or from prey that harbor the parasite.  Large numbers of eggs can be spread into the environment by an infected dog or cat.

Roundworms can lead to a host of medical problems in dogs, including stunted growth among puppies that are infected early in their development.  Puppies are more likely than adult dogs to develop serious symptoms.  Fortunately, there are safe and effective treatments and measures of prevention that will keep canines healthy and limit the spread of infection to others.  Diarrhea and vomiting are common symptoms of roundworm infestation, and can lead to dehydration. Generally, the infection has a more serious impact on kittens than on adult cats, which may show no outward symptoms of the disease. Nevertheless, all cats and kittens, even those who are asymptomatic, should be dewormed because roundworms can cause illness in humans.

Young children who play in uncovered sandboxes or dirt where outdoor cats have been known to defecate are especially at risk for contracting the parasite. Although uncommon, roundworm infection can lead to serious diseases in humans, including blindness and disorders of the central nervous system.

Hookworms are small, blood-sucking worms that actually have heads that “hook” into the small intestine, where they begin to eat away at the tissue and suck blood.  This parasite can pose severe health problems for puppies and kittens because they have a lower blood supply than adults and can suffer from the adverse effects of blood loss (anemia, diarrhea, weight loss, and possibly death) more quickly. 

Eating a rodent infected with hookworm larvae, or ingesting hookworm larvae directly, are the most common way that one acquires these worms. Symptoms are usually lethargy, diarrhea (or dark stools due to blood in stool), weakness and vomiting.  Hookworms are about a 1/2 inch long, slim and threadlike.  They are so small that they cannot be seen by the naked eye in your pet’s feces so microscopic evaluation is necessary.  Because the larvae spread through feces, it is extremely important to thoroughly clean and disinfect affected areas.  Always pick up after your pet goes to the bathroom and practice prompt cleaning of litter boxes to minimize the chance of re-infection.  Hookworm larvae can also penetrate the skin of humans and cause dermatitis.

This is a common intestinal parasite and is more frequently found in cats. Tapeworms infect when a cat ingests a host such as a rodent, rabbit, or adult flea harboring infective tapeworm larvae. Tapeworms irritate a cat's rear end and cause itching, but generally do not pose a severe health risk to the animal.  Underweight cats and young kittens that become infected with tapeworms can lose valuable nutrients and fail to gain weight.  Medications are available that effectively eliminate the parasite but preventative measures should be initiated to discourage new infections from taking place.

Tapeworms do not cause harm to the dogs they infect, although minor irritation to the anal area may occur. Dogs can become infected with tapeworms in one of two ways. Adult fleas may carry infective tapeworm larvae.  As with a cat, when a dog chews at himself he may accidentally swallow the fleas and then become infected. Less commonly, dogs can become infected when they eat a rabbit or rodent, which can harbor different species of the tapeworm.

The adult tapeworm is made up of many small segments, each about the size of a grain of white rice. Usually, single segments -- which contain tapeworm eggs -- break off the tail end of the tapeworm, and are passed into the stool. These segments can be noted on the fur around the anus or in the feces.  Although uncommon, cats potentially can spread Echinococcus eggs to a human, making him or her a host for the parasite.

Whipworms are parasites that get their name from the whip-like shape of the adult worms. The front portion of the worm is very thin (the whip) and the end is thick (whip handle).  Dogs can get whipworms by eating dirt that contains the infective eggs of the adult parasite. Very rarely, cats are affected by whipworms.

Whipworms are dangerous because they can cause intestinal inflammation, bleeding, and sometimes the loss of protein. Puppies with severe infections can become extremely ill.

Ingesting food or water contaminated with whipworm eggs will infect a dog or cat. The eggs are swallowed, hatch, and in three months, the larvae mature into adults in the cecum and large intestine where they burrow their mouths into the intestinal wall and feed on blood. Adult worms lay eggs that are passed in the feces. The eggs must remain in the soil for about a month to mature and be capable of causing infection.  An infection is diagnosed by finding the eggs in the feces.  It is important to understand that the eggs can remain infective where animals defecate for a very long time and can be difficult, if not impossible, to eliminate from the environment. Consequently, cleaning up after your pet immediately is as important as preventative care.  For further information, talk with your veterinarian. 

To keep your pet free from internal parasites, the following is recommended:

  • Make sure to have your dog tested for heartworm annually and place him or her on preventative medication.
  • Have periodic stool evaluations performed by your veterinary office.
  • Maintain a clean environment by promptly removing waste from the area where your pet goes to the “bathroom.” 


Internal Parasites in Pets

Connecticut Humane Society

701 Russell Road, Newington, CT 06111
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The Connecticut Humane Society is a 501(c)(3)
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Copyright 2013 Connecticut Humane Society

Copyright 2013 Connecticut Humane Society