Common Dog Parasites

You may try to do everything you can to protect your pet and keep them happy and healthy, but according to the Companion Animal Parasite Council, many dogs will be affected by parasites at some point in their lives. These small—sometimes microscopic—organisms carry disease and can cause serious illness in our four-legged family members if not taken care of quickly.

“Parasites can cause many dangerous health issues including anemia, gastrointestinal upset, extreme weight loss and blindness,” says Dr. Ashley Rossman, owner of the Glen Oak Dog and Cat Hospital in Glenview, Illinois.

To protect your dog, familiarize yourself with common parasites in dogs and learn how to prevent and treat each of these dangerous pests.

Types of parasites in dogs

There are two categories of parasites in dogs that pet parents should be aware of: internal parasites and external parasites.

Internal parasites, often in the form of worms, can be transferred in various ways but live inside the body and can affect a number of organs. External parasites—such as fleas & ticks—land on or crawl up a dog’s body and feed off of a dog’s blood.

Intestinal parasites in dogs

Considered an internal parasite, intestinal parasites are usually ingested by dogs and affect a dog’s gastrointestinal tract. The most common types of intestinal parasites in dogs are roundworms and hookworms, says Rossman.

“Roundworms are primarily transmitted through the fecal-oral route, meaning they are transmitted through ingestion of fecal material,” she says. “Hookworms are often transmitted to puppies in their mother's milk. Hookworms can also be transmitted through an infected environment or contact with fecal material.”

Both of these intestinal parasites in dogs can cause serious side effects, and pet parents shouldn’t put off or delay treatment. “Anemia, blindness and possible death are just a few outcomes of parasitic infestation,” says Rossman.

Other types of intestinal parasites in dogs include:

  • Whipworms
  • Tapeworms
  • Giardia
  • Coccidia

Intestinal parasites, says Rossman, are typically transmitted when a dog unknowingly ingests parasite eggs or spores in contaminated food, animal feces, water or soil. Some intestinal parasites, including hookworms and roundworms, can also be transmitted to people and cause illness. The Centers for Disease Control and Prevention advises, “Avoiding skin contact with sand or soil, and regular veterinary care for your pets—including deworming—will help ensure healthy pets and healthy people.”


Heartworms are another type of internal parasite and are transmitted to dogs through mosquito bites. An adult heartworm produces larvae in a dog’s bloodstream, and these worms grow and eventually affect a pet’s heart and lungs, potentially leading to congestive heart failure and death.

According to the FDA, heartworms can live inside a dog for five to seven years and grow from 4 to 12 inches in length.

External parasites in dogs

Fleas & ticks are the most common type of external parasites that affect dogs.

“Dogs can become infected with ticks when they go to heavily wooded areas, areas with tall grass or areas populated with deer,” says Rossman. “Dogs can obtain fleas from other affected animals, or environments that have a heavy flea burden.”

Ticks can transmit a variety of dangerous and life-threatening diseases including:

  • Lyme disease
  • Ehrlichiosis
  • Rocky Mountain spotted fever
  • Babesiosis
  • Tick paralysis

Fleas—in addition to making a dog uncomfortable and itchy—can create more serious problems for dogs. “Flea infestation can cause anemia and severe dermatitis,” says Rossman.

If pets bring fleas & ticks into your home, it’s also possible for these parasites to affect human family members and pass on discomfort and disease. Pet parents should be vigilant about checking for fleas & ticks and using veterinarian-prescribed pest medications to prevent infestations. There are also many effective over-the-counter flea & tick medications that don't require a prescription.

Symptoms of parasites in dogs

Symptoms of a parasite infection in dogs will depend on the type of parasite.

Rossman recommends that pet parents practice year-round flea & tick and heartworm prevention and conduct regular external checks to look for fleas or ticks.

“Pet parents should always visually inspect and then run their fingers through their pet’s hair after going outside to make sure that no ticks have taken up residency on their dog,” she says.

She also says that pet parents should see a veterinarian if their dogs show the following symptoms:

  • Diarrhea lasting more than 24 hours
  • Coughing
  • Weight loss
  • Lethargy
  • Hair loss, skin hot spots or severe itching

“If a pet parent feels that their dog is just not behaving normally, they should certainly consult their veterinarian,” Rossman adds.

Treatment and prevention of parasites in dogs

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Preventing a parasite problem before it starts is always ideal. By having your pet on a method that protects from heartworm, fleas & ticks, you can keep them out of harm's way and avoid any larger issues later on. Treatment for parasites will depend on the type of parasite infection, and pet parents should consult their veterinarian to identify the right treatment option for their dogs.

For internal parasites such as roundworms, hookworms and tapeworms, your veterinarian may prescribe a deworming product. Many dewormers can be administered orally and are prescribed by veterinarians or found over the counter, without a prescription.

Treatment for heartworms is more complex and often involves a stabilizing period of steroids, heartworm preventives and antibiotics before actual treatment to kill the worms begins.

There is one FDA-approved treatment that kills heartworms and it is administered to dogs via injection. Dogs are often given three rounds of the injection during treatment, which could last 30 to 60 days. Dogs being treated for heartworm need to be closely monitored at a veterinary office or hospital while undergoing treatment. Following treatment, dogs require exercise restriction.

In severe cases of heartworm disease, surgery may be recommended by your veterinarian. Because of the very involved, and often expensive, treatment of heartworm, it is very important for pet parents to consult their veterinarian about the appropriate heartworm preventive for their dog to be on.

Flea & tick preventive medications are the best way to protect your pet as they are effective at treating certain intestinal parasite infections in dogs once administered. These medications can be given orally, applied topically, or administered through collar-like products. By administering ongoing prevention medication, you can keep your pet safe as well as avoid potentially very costly deworming treatments.

Regular veterinary checkups can catch parasites early and even potentially help prevent parasite infections in dogs.

“It is very important to have your veterinarian evaluate the dog’s stool sample one to two times per calendar year,” says Rossman. “Heartworm testing should also be done on a yearly basis, and more often if there are any breaks in prevention. It is always better to catch a parasitic infection early before it starts to cause clinical signs.”

If your dog is showing signs of a parasite or it’s time to schedule their annual exam, consult your veterinarian today.