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What are Types of Dog Parasites?

Our furry friends like to go everywhere with us, especially outside. But what dangers lie (or crawl!), outside? Canine Parasites. Creepy little creatures that can cause so much damage to our beloved pets. Whether the effect is immediate or delayed, they certainly will adversely affect your pet’s health or comfort levels.

There are three general types of dog parasites: internal, external, and intestinal. While each type of dog parasite could be a post of its own, we’ll briefly introduce each today.

Internal Dog Parasite Archenemy: Heartworm

The most common internal parasite is heartworm in dogs, which can potentially be fatal if left unchecked. Heartworms are transmitted to dogs via the bite of an infected mosquito, where the heartworm then travels to the heart through the bloodstream and matures.1 As it matures, the heartworm will clog the dog’s heart, slowing down blood flow to the body. Symptoms of heartworm include a cough, fatigue, and reduction in appetite, though some dogs can be asymptomatic.1 Antigen blood tests by your veterinarian are the most common way to confirm heartworm in dogs and chest x-rays typically asses the severity and extent.

Prevention measures, especially in areas with large mosquito populations, are highly recommended. There are several heartworm preventatives for you to consider, including Heartgard®, Interceptor®, Trifexis® etc.Treatment can be long and costly, so it’s important to research and see if a preventative is right for you and your pup.

Common External Dog Parasites: Dog Lice, Fleas, and More

Next on the list are external parasites, such as dog lice, fleas, ticks, and mites. These critters can be acquired by just going outside and exploring with your furry friend or frequenting spaces with other infected animals. Identifying dog lice, fleas, ticks, and mites with the naked eye is relatively easy since they're external and can be found on the fur and skin with a thorough search immediately following any outdoor adventures. Below are pictures of fleas (left) and four different species of female ticks (right).1

flea image for identification on dogs  female ticks for identification on dogs

As with heartworm, there are several preventatives, including NexGard®, Trifexis®, Bravecto® etc.3, that vary in form from oral tablet to wearable. (Please note that for all drugs, including human drugs, you should always be aware of potential side effects.) In addition to the aforementioned drugs, there are also many natural flea and tick preventatives, including diluted essential oils (dogs have sensitive noses!), use of herbs, apple cider vinegar, castile soap baths, and diligent physical checks. We encourage you to discuss a preventive flea and tick approach with your veterinarian, assessing geographic location, lifestyle, season, and more.

Intestinal Parasites in Dogs: Worms and Protozoans

Intestinal parasites in dogs are worms, including but not limited to hookworms, ringworms, roundworms, tapeworms, and whipworms, as well as protozoans like coccidia, giardia, and spirochetes.1 So how do these intestinal parasites even get in our dogs’ intestines? Our dogs ingest the adult parasites or their eggs when they eat grass or dirt, or even intermediate hosts like fleas, rabbits, rodents, etc.Common symptoms of worms in dogs include diarrhea (there may be blood or excess mucus present), weight loss, and reduction of appetite.1

Even though intestinal parasites in dogs physically reside inside our dogs, they can be detected by closely examining your dog’s feces. To do this, you will need to provide a fresh fecal sample to your veterinarian, who will look for larvae or adult worms under a microscope. In some instances, you may even be able to see adult worms in in your dog’s poop! Worms in dog poop can appear as long strings, while tapeworms in dog poop may resemble pieces of rice.

While there is no treatment for intestinal parasites in dogs or giardia in puppies, your veterinarian may off-label prescribe drugs, such as metronidazole, to help attack the parasites during their infectious stage (often by killing the larvae) to stop their lifecycle and slowly help your dog naturally expel the parasites.

Worms in dogs, such as roundworms, hookworms, and tapeworms4, are zoonotic in nature, meaning that they can be transmitted from an animal to a human. It’s important to always wash your hands after encountering your dog’s poop and clean your home and dog’s toys, blankets, and beds often.

common worms in dogs

Being mindful of common types of dog parasites and taking care to prevent them from infecting your dog will help save precious hours and dollars trying to treat any infections, which may result in weeks or months of discomfort for your precious pup! Additionally, avoiding the need for drug treatments will help preserve your dog's sensitive gut microbiome and immune center from disruption.


  1. Hendrix, Charles M., and Ed Robinson. Diagnostic Parasitology for Veterinary Technicians. 5th Elsevier Inc., 2017.
  2. Aurora Animal Hospital. Heartworm. 2020.
  3. Aurora Animal Hospital. Flea and Tick. 2020.
  4. Zajac, Anne M., and Gary A. Conboy. Veterinary Clinical Parasitology. 8th John Wiley & Sons, Inc., 2012.
  5. Common Worms in Dogs via