Brentwood Animal Hospital

3900 Rhode Island Avenue
Brentwood, MD 20722


Internal Parasites


Protect Your Pets From Internal Invaders

Someinternal parasites, heartworms in particular, can be deadly if not treated.Prevention is much easier than treatment. Other internal parasites may notalways be lethal but can still cause great misery for your dog or cat.


Heartwormsinfect both dogs and cats. These invaders are transmitted by mosquitoes whenthey are in a microscopic larval stage. Once inside your pet, they growdramatically and migrate to the animal's heart and lungs. Adult heartworms canreach 7-10 inches in length. Adult heartworms can begin to cause damage to theheart and lungs as soon as they arrive. Microfiliaria circulating in the dog,in large enough numbers, can also cause damage in the organs in the body. Theseparasites can do tremendous damage to a dog's heart, triggering congestiveheart failure and death if left untreated. While heartworms are less common incats, they are by no means uncommon. It is estimated that 17 percent of cats inthe U.S. have the disease, and it is fatal in 10-20 percent of cases. Whenheartworms infect a cat, they primarily affect the lungs, causing a conditionknown as Heartworm-Associated Respiratory Disease (HARD). They can causepermanent lung damage in both cats and dogs. Symptoms include coughing,wheezing, shortness of breath, rapid breathing, vomiting, and weight loss.Symptoms may not show up until the disease is quite advanced.

Becausethey are spread by mosquitoes, heartworms are a particular problem in any areawhere mosquitoes thrive--including Texas and the U.S. Gulf Coast. Sincemosquitoes sometimes get in the home, even indoor dogs and cats are at risk.There is no treatment available for cats that will kill heartworms, butcorticosteroids can help reduce inflammation of the pulmonary system. Cats mayclear a heartworm infection without treatment, but they may be left withpermanent damage to the lungs and related structures. Treatment to killheartworms is available for dogs, and it can save their lives if the infectionis caught in time. Even with medication, some dogs may not recover, especiallyif the infection is advanced. Treatment takes many months, and the dog'sactivities must be severely limited until treatment is completed. SNAP does nottreat ill or injured animals, so you will be referred to a full-serviceveterinarian if your animal is believed to be infected.

Preventingheartworms is the key. Heartworm prevention is available for both dogs and catsand kills the parasite while it is still microscopic in size--thus preventingfurther harm to the animal. Dogs can only be put on prevention if they are notalready infected, so they must be tested first. Cats can be put on prevenativeeven if they are already infected, and doing so may somewhat limit theinfection thus speeding recovery.

Preventioncan be started at a puppy’s first vaccine at 6-8 weeks of age. It is givenevery 30 days throughout the dog’s life. Dogs 7 months of age and younger maystart heartworm prevention without a heartworm test.

Heartwormprevention medicationss are effective if given monthly and at the correct dose.The correct dose is vital, do not under dose. If a dog is on the high edge of aweight range, it is safe enough to use the next higher weight range dose incase the dog gains weight, e.g. a 24 pound dog may be given the 25-50 pounddose of Heartgard. Heartworms may be adapting, and if medications are not givenevery 30 days and at an adequate dose, they may develop the ability to slipthrough our defenses and complete the life cycle. This means adult heartwormsin the heart! Be sure to inquire about heartworm testing and prevention whenyou bring your animal in for a wellness exam.

Intestinal Parasites

Intestinalparasites can be difficult to eliminate and may require multiple treatmentswith deworming medications. This section describes the most common intestinalparasites and what can be done to free your pet from their gruesome grip.


Roundwormsaffect both cats and dogs. They can grow up to five inches in length.Roundworms are transmitted through ingestion of contaminated feces. Kittens andpuppies can become infected while nursing, and puppies may be infected atbirth. Roundworms attach themselves to the intestinal wall and feed on ananimal's blood. During the larval stage, roundworms may pass through the lungs.This can cause coughing or gagging, especially among kittens and puppies. Thelarvae are coughed up, swallowed, and pass to the small intestines to matureinto adult roundworms. A severe infestation can be deadly for a kitten orpuppy. Roundworm eggs can be excreted in stool, and worms themselves can appearin vomit or stool. They are usually white or brown in color and may still bealive. Roundworms are zoonotic--they can be passed from animals to human.Symptoms include coughing, abdominal pain, nausea, diarrhea, blood in stool, orweight loss. This parasite also causes a bloated stomach appearance, common inpuppies. When people ingest the larvae, they travel through the liver, lungs orother organs. This is called visceral larval migrans. SNAP wellnessveterinarians can administer deworming agents that will kill roundworms in yourpet's digestive tract.


Whipwormsare a form of roundworm. Their name comes from the fact that they are thin atone end and have a thick section at the other end that resembles the handle ofa whip. Whipworms primarily affect dogs and live in the cecum, which is betweenthe small and large intestines. There is a form for whipworm that affects cats,but such infections are fortunately rare. Whipworms are transmitted by theingestion of infective eggs. Eggs live in the environment, soil, or in animalfeces. They are extremely persistent even in harsh environments. An infectedanimal may show no symptoms, but severe infections may cause bloody diarrhea.Because the worms feed on the animals blood supply of the large intestines,they can also cause anemia. This parasite can be difficult to kill and mayrequire repeated treatment with deworming medication.



Theseparasites are named for the hook-like mouth structures they use to attachthemselves to your animal's intestinal wall. Hookworms are small--less than aninch long. Like most intestinal parasites, their eggs are passed in stool andhatch into larvae. They are transmitted when another animal ingests or comesinto contact with contaminated soil, water, or stool. Hookworms are more commonin dogs, but affect cats as well. Once a hookworms has attached itself to theanimal's intestinal wall, it will feed on the animal's blood supply. It maytherefore cause cause anemia. Hookworms, like roundworms, are zoonotic. Theycan be contracted when walking barefoot or while sitting on contaminatedground. SNAP wellness veterinarians can administer deworming agents that willkill hookworms. Symptoms include blood in the stool, diarrhea, fever, loss ofappetite, and anemia (which can cause gums to appear pale). Hookworm larvae areinfective to people also, and move within the skin causing inflammation. Thisis called cutaneous larva migrans.

Some of the information in this section comes from the CDC webpage on hookworms.


Tapewormsare very common among our pets and for very good reason. They are transmittedby fleas. Specifically, tapeworm larvae are present within the fleas that seekout your dog or cat. When the animal bites at the fleas, they can be ingestedinadvertently. The larvae is thus introduced into the digestive tract where itattaches itself to the intestinal wall. There it can grow to be up to two feetin length. The adult tapeworm produces eggs which are contained within its bodysegments. These segments break off and pass out of the animal when itdefecates. They can sometimes be seen in the stool or on the fur around a pet'sperianal region. They are similar in appearance to a grain of rice. They maymove. Symptoms include poor hair coat, abdominal pain, diarrhea, lethargy,weight loss, or itching around the anus. If you observe these symptoms or seetapeworm segments on your pet or in his or her stool, the animal should to betreated to eliminate the parasite.

Becausetapeworms are spread by fleas, canine and feline flea prevention is aneffective means of protecting your furry friend against tapeworms. SNAPwellness clinics sell several popular and effective brands.


Giardiais a parasitic disease of the intestinal tract. It is transmitted through contaminatedwater. This disease is zoonotic--it can be transmitted to humans. Symptoms mayinclude diarrhea, vomiting, weight loss, or poor overall condition.


Coccidiais a parasitic disease of the intestinal tract of animals caused by coccidianprotozoa. It spreads from one animal to another through infected feces oringestion of infected tissue. Young or immunocompromised animals may suffersevere symptoms and death. The primary symptom of coccidia is diarrhea, whichmay become bloody.


Contraryto common belief, dogs and cats do not carry pinworms. They cannot thereforetransmit them to human children (or adults).