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Anthelmintics for Dogs and Cats: How to Stay Safe

Intestinal worms are a worldwide health concern for dogs and cats. An important part of pet ownership is protecting your pet from intestinal parasites by using anthelmintics. Learn what anthelmintics are, how they’re used in pets, and how to keep yourself safe as a pet owner.

Understanding intestinal worms in pets

Intestinal helminths (parasitic worms) that commonly affect dogs and cats include roundworms, hookworms, whipworms, and tapeworms. While roundworms, hookworms, and tapeworms are commonly found in both dogs and cats, whipworms are quite rare in cats.

These parasitic worms live in your pet’s intestines, either stealing nutrients from your pet’s digested food or feeding on your pet’s blood. Specifically, hookworms are blood-feeding parasites.

Intestinal worms can be contracted by pets in several ways:

  • Across the mom’s placenta while in utero: roundworms (dogs), hookworms (dogs)
  • Through the mom’s milk during nursing: roundworms, hookworms (dogs)
  • Through ingestion or licking of items contaminated by feces: roundworms, hookworms, whipworms (dogs)
  • Through ingestion of other parasite hosts: tapeworms, roundworms, hookworms
  • By passing through the skin: hookworms

Because transmission can occur from mother to offspring, roundworms and hookworms are quite common in puppies and kittens. Worms that are transmitted due to fecal contamination are often found in parks, playgrounds, yards, and beaches. Tapeworms are common in pets who have had fleas or are allowed to eat rodents.

The symptoms of an intestinal worm infestation include:

  • Vomiting
  • Diarrhea
  • Weight loss
  • Unthrifty appearance
  • Visible worms in stools
  • Rice-like segments on the patient’s perineum or in their resting areas (tapeworms)
  • Pale gums and lethargy due to anemia (hookworms)

Signs of worm infestation are more common in puppies and kittens than in healthy adult animals. You may also see signs in immunocompromised patients, elderly patients, or patients who have very high numbers of parasites. Despite popular belief, butt-scooting is not a common symptom of intestinal worms in dogs or cats.

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Zoonotic potential of helminths in pets

Diseases that can pass from animals to people are called zoonotic diseases. Some gastrointestinal parasites in dogs and cats also have the potential to affect human family members. Tapeworms, hookworms, and roundworms all have zoonotic potential.

  • Tapeworms. Humans can get tapeworms if they accidentally ingest fleas that are carrying tapeworms. This is more common in children.
  • Hookworms. Humans can also contract hookworms through the skin if they walk or play in areas with hookworm larvae, such as sandy beaches. In people, hookworms cause cutaneous larva migrans (CLM), a red and itchy skin condition caused by hookworm skin infection.
  • Roundworms. A person can contract roundworms if they accidentally ingest something that is contaminated with fecal matter (also more common in children). In humans, the roundworm larvae migrate through the intestinal wall and are carried around to different parts of the body in the bloodstream. Ocular larva migrans (OLM) occurs when the larvae migrate into the back of the eye, causing inflammation in the eye and eventual vision loss.

Concerns over contracting worms from pets can lead to some pet owners wondering if they too should take parasite-killing medications, or anthelmintics.

What are anthelmintic drugs?

Anthelmintics for dogs and cats are medications that will kill or remove intestinal worms from the pet’s body. The drugs primarily work in two ways:

  • Targeting neurologic channels that are unique to the parasite, leading to parasite paralysis and eventual death.
  • Disrupting the parasite’s cellular functions so that the cells can’t produce energy or undergo cellular division.

Examples of common anthelmintics include pyrantel, praziquantel, febantel, fenbendazole, moxidectin, selamectin, ivermectin, and milbemycin oxime. This antiparasitic drug list does not cover all possible anthelmintics that could be recommended by your veterinarian.

Anthelmintic drugs are available as oral tablets, chewable treats, topical solutions, and injectables. Some are one-time treatments, while others are recommended as monthly preventatives.

Keeping your pet worm-free: anthelmintic use in dogs and cats

Regular deworming is important for pets to prevent worm infestations. Your veterinarian will recommend specific deworming schedules for puppies, kittens, and adult pets based on your pet’s risk factors. These risk factors include your pet's age, geographic location, and lifestyle.

General examples of deworming schedules are included below:

  • How often to deworm puppies and kittens: Begin administering anthelmintics when the puppy or kitten is two weeks old. Repeat every two weeks or at the time of vaccine boosters until the animal is on regular broad-spectrum parasite preventives.
  • How often to deworm adult dogs and cats: Adult animals should be on year-round parasite preventives, usually a monthly chew/tablet or topical. Additional anthelmintics are prescribed as needed. If not, quarterly deworming is recommended.

For pets with gastrointestinal symptoms, the veterinarian may recommend testing the dog or cat's feces for worms and other gastrointestinal parasites. Because gastrointestinal parasites are so common, some veterinarians recommend that you routinely get fecal testing for your pet at wellness visits. The results of the fecal testing can drive what anthelmintics your veterinarian recommends.

Generally, veterinarians recommend broad-spectrum preventatives that prevent intestinal parasites, heartworms, and fleas. The Companion Animal Parasite Council (CAPC) provides general recommendations for all dogs and cats.

A veterinarian is your best source for diagnosis of parasitic infestations and treatment recommendations for your individual pet.

Why not humans? Safety concerns and alternatives

Anthelmintic drugs formulated for pets are not safe for human consumption. The dosing is intended to be efficacious for your pet and can easily lead to an overdose in a human. Some of the inactive ingredients found in animal dewormers have not been evaluated for use in people.

If you are concerned that you've contracted parasites from your pet, speak with a physician. There are medications that are used to treat worms and other parasites in people. However, many of these drugs have significant side effects and should not be used routinely to prevent helminth infections. These medications should only be used if you have been diagnosed with a parasitic infection. In this case, your doctor will prescribe the medication right for you.

Do not take an anthelmintic medication without discussing its use with your physician. Do not take anthelmintics that are intended for pets.

Keeping your human and animal family members healthy

The following tips will help you protect your pets and human family members:

  1. Follow your veterinarian’s recommendations for how to prevent worms in dogs and cats to decrease the risk of contracting parasites from your pet.
  2. Cover sandboxes when not in use to discourage outdoor animals from using them as litter boxes.
  3. Keep your cat and dog anthelmintics out of the reach of children and pets. Pets who enjoy the taste of their preventives may consume all at once if allowed.
  4. Make sure not to apply dog parasite prevention to cats and vice versa. Permethrin is often found in dog parasite preventatives and is toxic to cats. Avoid using permethrin-containing parasiticides if you have a cat in the home.
  5. Store pet medications in their original containers with proper labeling. If prescribed by a veterinarian, the medication should have a prescription label.
  6. Clean up after your pet by disposing of dog feces in a bag and regularly cleaning the litter box. It is important to clean your yard at least once a week to reduce the risk of contamination.
  7. Practice good personal hygiene and always wash your hands after playing outside or with your pet. This is especially important to do so before you eat.
  8. Pay close attention to your children and pets when they are interacting with one another.

Speak with your veterinarian about deworming and parasite preventives for your pet. For most pets, year-round parasite prevention is recommended to protect the pet from not just intestinal worms, but also heartworms, fleas, and ticks. The best way to protect your human family members from parasites is to protect your animal family members from parasites.


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