Pesky Cat Internal Parasites

Just thinking of cat internal parasites...organisms that survive by taking nutrition from other enough to put a shiver down your back. Residents like worms living inside your cat...Yuk! These internal parasites often give no hint they are there until your cat seems ill. A kitten can become extremely debilitated by this internal invasion and a heavy worm burden in a kitten can be life threatening. Take your cat to the vet to investigate further.

Diagnosing Intestinal Infection

In order to determine whether your cat is infected with gastrointestinal parasites your vet will analyze a sample of your cat's feces for worm eggs, larvae, or pieces of worms. This can help him identify the species of worms your cat is infected with so he or she can choose a medication that kills those species.

Don't be surprised if your vet treats your cat with a medication that kills other species of cat internal parasites as well...because cats can be infected with several types of worms at once, yet only show evidence of one.

Gastrointestinal Parasites

Some of these cat internal parasites are worms, while others are single-celled organisms called protozoa. WORMS: The two types of worms that can infect cats are roundworms (the most common in cats) and tapeworms. The two species of roundworms that can infect cats are Toxocara cati and Toxascaris leonina. Adult cats infected with either of these roundworms usually don't show observable signs of infection.

But infected young cats may lose weight, vomit, have diarrhea, lack energy, develop a pot belly, and have a poor hair coat. Some cat internal parasites infect nursing kittens by being in mom's milk. Your vet can give you a medication that will rid your cat of those but some medications only kill the adult worms so you may have to repeat the process a few weeks later.

The two species of tapeworms that can infect cats are: Dipylidium caninum which is transmitted by fleas(it lives in the stomach of the flea and is ingested by your cat when it grooms) and is the most common.

If your cat tries to rid himself of fleas by licking them off, he ingests the tapeworm larvae with the flea. As the flea's body is digested within her, the tapeworm is released and attaches to the wall of the cat's small intestine, where it will live indefinitely. During its life the tapeworm releases segments of its body into your cat's feces, and you find these segments (which are laden with eggs for new tapeworms) in fresh feces or in the fur around your cat's anus.

The second is Taenia taeniaformis which is transmitted by small rodents and rabbits. Cats may ingest parasites while hunting small rodents such as mice and squirrels because the prey may harbor the tapeworm. A tapeworm infected cat doesn't usually show signs of infection. The clue is shriveled-up worm segments...which look like grains of rice...around your cat's anus or on the cushion where your cat sits.

Your veterinarian can prescribe a dewormer to kill tapeworms but to prevent reinfection, you'll have to keep him away from the animals that transmitted the worms to him...keep him indoors...and eliminate fleas. For a good selection of dewormers from reliable vendors see the Pet Products page.

There are lots of protozoans that can infect cats but people are most concerned about Toxoplasma gondii which can cause toxoplasmosis. Cats infected with T. gondii usually don't show signs...unless it has migrated from the gastrointestinal tract to organs such as the lungs or brain.

Humans can also become infected with T. gondii by picking up the parasite when handling or eating raw or undercooked meat but you can also get the parasite from an infected cat's feces. People with fully functioning immune systems may only suffer a brief flu-like illness. Most cats develop immunity to the cat internal parasites a couple of weeks after infection.

The protozoan Isospora can also infect cats. Adult cats usually don't show signs, but kittens may develop bloody diarrhea. Your vet can give your kitten medication to rid him of the parasite. A third protozoan, Giardia also infects cats but usually causes no signs in older cats. However, if a young cat is infected, it may lose weight and fail to grow normally. Again, your vet can give you medication to kill the parasite.

There are also cat internal parasites like Giardia that can infect a cat who drinks stagnant water contaminated with the protozoa. If your cat goes outdoors, make sure he always has access to fresh water. Other parasite infections are passed through feces. Some parasite eggs take several days or even weeks to become infectious so a daily litterbox cleaning reduces infection risks.


The heartworm...known as Dirofilaria immitis is less common than the gastrointestinal parasites but more difficult to treat and diagnose. Heartworm larvae can infect your cat when a larvae-carrying mosquito bites your cat. The larvae slowly migrate to your cat's heart and pulmonary arteries, where they mature into adults. Fortunately, the cat's immune system attacks and kills many of the larvae enroute to the heart.

But if your cat's immune system misses even one, that single larva can mature into an adult and cause your cat to cough, periodically vomit, and be short of breath. You can purchase heartworm prevention products as well as other meds, again, check the Pet Products page.

If your cat is diagnosed with heartworm, you and your vet will have to discuss treatment options. The medication used to kill adult worms (an adulticide) has caused serious side effects in some cats...even death. Some vets have successfully treated heartworm infected cats with the adulticide and feel confident in recommending the treatment.

But since heartworms only live a few years inside a cat, some veterinarians will put the pet on heartworm preventive medicine to avert further infection, then monitor the cat until the existing worms die. An infected cat may also be put on the corticosteroid prednisone which reduces the body's allergic response to the worms and may relieve the clinical signs.

Related Articles......

Cat Constipation

Fleas on Cats

Cat Vomiting

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