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Intestinal parasites are very common in both dogs and cats. These parasites are often transmitted just after birth from the mother through nursing, and in some cases can even be transmitted to puppies and kittens before they are born! Adult pets can pick up intestinal parasites from the environment by licking and chewing on contaminated objects. Routine screening and treatment for intestinal parasites is critical for the health and well-being of your pet. As you will read below, even people can benefit from the treatment of their pets as this helps prevent transmission of these parasites to humans as well.


Clinical signs manifested by pets that are infected with intestinal parasites can vary, and depend on a pet's age, nutritional status, parasite load, duration of infestation, etc. One of the most common symptoms of intestinal parasitism is diarrhea. Other symptoms include poor appetite, lethargy, coughing, and abdominal distention. Some pets don't show any symptoms while others can die from their infestation. Parasites tend to infest older and younger animals most commonly. Intestinal parasites can also make a pet more susceptible to other diseases.

Due to the prevalence of intestinal parasites in dogs and cats, their lack of symptoms in some cases, and the potential for humans to become infected, your pet's feces should be checked for parasites at least twice a year. Dogs and cats that are mostly outside and/or are exposed frequently to other animals (dog parks, etc.) should have their feces checked more often. Routine de-worming should be performed on all dogs and cats every 6 months if they are not currently on heartworm preventative medication, even if the stool check for parasites is negative.



Roundworms are the most common intestinal parasite in dogs and cats worldwide. Animals with roundworms pass the infection to other animals when the worm eggs develop into larvae and are present in the animal's feces. Your pet can pick up the infection by eating infected soil, licking contaminated fur or paws, or by drinking contaminated water. Infected female dogs may pass the infection to their puppies before birth or afterwards when they are nursing. Infected female cats cannot infect their kittens before birth, but can pass on the infection through their milk when kittens are nursing.

Puppies and kittens are the most prone to roundworm infection. Because roundworms live in the small intestine, they steal the nutrients from the food your pet eats and that can lead to malnutrition and intestinal problems. As the larvae move through your pet's body, young animals may develop serious respiratory problems such as coughing and pneumonia.

Roundworm infections are zoonotic (pronounced zoe-oh-NOT-ick) diseases, meaning that they are animal diseases that can be transmitted to humans. While direct contact with infected dogs and cats increases a person's risk for roundworm infection, most infections come from accidentally eating the worm larvae or from larvae that enter through the skin. For example, children are at risk for infection if they play in areas that may contain infected feces (such as dirt piles and sandboxes). They pick up the larvae on their hands and then the parasite can easily be ingested. Left untreated, roundworms in people can cause serious health problems when the larvae enter organs and other tissues, resulting in lung, brain, or liver damage. If the roundworm larva enters the eyes, permanent, partial blindness can result.


Hookworms are the second most common intestinal parasites found in dogs, but they are less commonly found in cats. Your pet can become infected when larvae penetrate the animal's skin or the lining of the mouth. An infected female dog can pass the infection to her puppies through her milk, but this does not occur in cats. Unlike roundworms, hookworms cannot be transmitted through the placenta prior to birth.

Hookworms are dangerous parasites because they actually bite into the intestinal lining of an animal and suck blood. As with roundworms, puppies and kittens are at high risk of infection and developing severe diseases. Left untreated, hookworm infections can result in potentially life-threatening blood loss, weakness, and malnutrition.

Like roundworms, hookworm infections are zoonotic, and can affect humans.

Infections usually occur by accidentally eating the larvae or by the larvae penetrating through the skin. In humans, hookworm infections cause many health problems. The larvae produce severe itching and tunnel-like, red areas as they move through the skin and, if accidentally eaten, can cause intestinal disease.


Whipworms are common in dogs and found throughout the United States. One species may rarely be found in cats, and more commonly in cats in foreign countries. Whipworms 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 other end is thick (whip handle). Whipworms live in the large intestine. Animals with whipworms pass the infection along to other animals when the worm eggs develop into larvae and are passed in their feces. Your pet can pick up the infection by eating infected soil or licking their contaminated fur or paws.

Like hookworms, whipworms bury their heads in the lining of an animal's intestine and suck blood. The signs of infection vary with the number of worms in the intestine. Small numbers of worms cause no signs, but larger numbers can result in inflammation of the intestinal wall. Severe infections can develop and lead to diarrhea and weight loss. Large amounts of mucus are produced by the inflamed intestine. Sometimes hemorrhage into the intestine occurs, and anemia can result. Whipworm larvae rarely infect humans when they are accidentally eaten. People are much more likely to be infected with Trichuris trichiuria - the human whipworm.


Tapeworms got their name because they are thin and flat, like strips of tape. Unlike the smooth-bodied roundworms, hookworms, and whipworms, tapeworms' bodies are actually made up of joined segments. Dogs and cats become infected with tapeworms when they eat infected fleas or lice. They can also get certain types of tapeworms by eating infected rodents.

Tapeworms live in the small intestine and steal the nutrients from the food your dog or cat eats. An infection is usually diagnosed when the eggs sacs are seen under the pet's tail or on its stool. These sacs look like flattened grains of rice. While there are several dewormers available that are effective against tapeworms, keeping your pet free of fleas is the best preventative. Rarely are tapeworms a risk to people.


Coccidia are single-celled parasites that infect the intestine. They are microscopic which means they are not visible to the naked eye. They are however, detectable on routine fecal tests in the same way that other parasites are. Coccidia are not worms and are not susceptible to de-worming medications.

Coccidia come from fecal-contaminated ground. Your pet can become infected by eating infected soil or licking contaminated paws or fur. Once swallowed, the parasites damage the lining of the intestine and your pet cannot absorb nutrients from its food. Bloody, watery diarrhea may result, and the animal may become dehydrated because it loses more water in its stool than it can replace by drinking. Young pets are most often infected because their immune systems may not yet be strong enough to fight off the parasite. Coccidia can be very contagious among young puppies and kittens, so households with multiple pets should be especially careful to practice good hygiene and sanitation. Coccidia infection is especially common in young animals housed in groups (in shelters, rescue areas, kennels, etc.) This is a common parasite and is not necessarily a sign of poor husbandry.  While there are species of coccidia that can infect people, the Isospora species of dogs and cats are not infective to people.

A routine fecal test by your veterinarian will detect the presence of coccidia. Treatment with specific medications will prevent the parasite from multiplying and allow time for your pet's immune system to kill the parasites.


Giardia is a microscopic single celled organism that is dangerous to virtually all warm-blooded creatures. If left untreated, Giardia can cause severe illness in pets and humans. This protozoan lives in the cells lining the beginning of the small intestine. Giardia kills these cells and severely damages the bowels. The infection can prevent the absorption of essential nutrients and vitamins, and the resulting malnutrition can endanger your pet’s health. With diminished resistance, other diseases can then attack your pet.

Giardia can be remarkably easy for your pet to catch: Just one lap of contaminated water or a bite on a contaminated stick is all it takes! The parasite is spread in the stool and can occasionally be passed on to you and other members of your family.

Because it is highly contagious among animals, good hygiene and sanitation are important when there are multiple pets in the household.

Giardia is harder to diagnose than other intestinal parasites, and several stool samples may have to be tested before it is found. There is a Giardia antigen test that uses a small swab taken directly from the rectum of your pet that increases the chances that the Giardia will be found. If necessary, your veterinarian will recommend treatment with medications to eliminate the infection.


The majority of intestinal parasites are diagnosed by microscopic examination of the feces for eggs that are released by the adult female in your pet's intestine. The number of eggs released in a given fecal sample can be variable, and sometimes they aren't any found even though your pet has an adult female parasite in its intestines. This means that a negative fecal report does not guarantee that your pet is free from intestinal parasites. In many cases we need to run numerous samples to feel comfortable that your pet is free of intestinal parasites.

In some cases our doctor's will treat for a specific parasite, even on a negative fecal sample, when they feel there is a likelihood of infestation, because some parasites eggs are notoriously hard to detect. In some cases a diagnosis is made by observation of the mature parasite in your pet's feces. This is especially true for tapeworms. Tapeworm eggs are difficult to detect during microscopic fecal analysis, so observation of the actual worm is how they are routinely diagnosed.


Intestinal parasites have very sophisticated life cycles that can make treatment difficult. Some of these life cycles involve mandatory maturation processes in other animals, including insects. Specific treatment modalities are set up to address these life cycles. It is important to follow treatment regimens precisely. Some parasites can only be controlled, not eliminated. In these cases it is important to check your pet's feces routinely and to use medication on a long term basis. There are many treatments for intestinal parasites that are very broad spectrum. They kill a wide variety of parasites, and they are the medications we use as a routine de-wormer. But please note, not all de-wormers will work for all parasites. An accurate diagnosis is important in determining the appropriate medication to use for each individual.

Monthly heartworm preventatives also contain intestinal parasite treatment which provides protection against many (but not all) intestinal parasites


Most people are aware of certain zoonotic diseases like rabies, anthrax and monkeypox because they are very serious, headline-grabbing diseases. However, the incidence of these diseases is very rare. In fact, there are only zero to two human cases of rabies annually in the U.S. Sadly, when it comes to the more common zoonoses like roundworm and hookworm, both of which can result in very serious health conditions, most people are unaware. More than 1/3 of the nation's dogs are infected with intestinal parasites. And the Centers for Disease Control estimates between one and three million people are zoonotically infected each year in the U.S.

As many as 4%–20% of children in the U.S. contract roundworms from their pets each year. In some parts of the country, especially the Southeast, zoonotically transmitted intestinal parasites are so prevalent that many children test positive for exposure to intestinal parasites and become sick. Children are one of the groups that are most susceptible to zoonotic infection because they are always grabbing, touching and sticking their hands in their mouths without regard to whether they are clean.

The good news is that the zoonosis phenomenon is entirely preventable. Using a year round parasite product to treat pets and reinforcing common sense hygiene in children helps families reduce the risk of contracting zoonoses.


Basic hygiene is essential in preventing zoonosis. Parents must wash the family's pets regularly and teach children about hands and mouths. Instruct children to wash their hands after playing with pets, after playing outdoors, before eating, and to wash often.

Some people are especially susceptible to zoonotic infections and parasites. Extreme precaution in preventing zoonotic transmission should be taken with immunocompromised individuals - people with HIV infection, people undergoing immunosuppressive therapy (e.g., chemotherapy patients, organ transplant patients, patients undergoing treatment for autoimmune disease), people with advanced liver disease, diabetics, pregnant women, infants and young children, and elderly individuals.

Here are some easy ways to help protect your family from internal parasites that can be carried by house pets:

  • Wash your hands with soap and running water after handling your pet - especially before eating or preparing food and after touching feces.
  • Keep your pet on monthly heartworm preventative which provides a once a month de-worming for your pet.
  • People with weakened immune systems should take special precautions, including never letting pets lick them on the face or on an open cut or wound, never touching animal feces and never handling an animal that has diarrhea.
  • Don't let your pet drink from toilet bowls or eat feces.
  • Shoes should be worn when outside to protect feet from larvae present in the environment.
  • Raw vegetables should be thoroughly washed because they may contain parasites from infected soil.
  • Keeping cats indoors is an effective way to limit their risk of exposure to roundworms.

You can reduce the risk of zoonotic infection by keeping your family's and pet's indoor and outdoor environments clean:

  • Remove your pet's fecal matter from your lawn or surrounding outdoor environment daily. Feces can be bagged and put in the trash, burned or flushed down a toilet.
  • Cover your children's sandboxes when not in use.
  • Use appropriate methods to reduce mosquito populations in your outdoor environment.


Healthy pets may not show outward signs of a parasite infection. However, if you notice a change in your pet's appetite or coat, diarrhea, or excessive coughing, see your veterinarian. In most cases, a simple fecal test can detect the presence of worm eggs or adults and, if present, your veterinarian will recommend a de-worming program. A good way to prevent worm infections is by using one of several monthly heartworm preventatives available from your veterinarian.

If you have any questions or concerns about zoonotic transmission of internal parasites or just want to schedule an appointment for an examination and parasite check please call the Merrick Veterinary Group at 516-379-6200 today.


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