The Center for Disease Control, or CDC, defines a parasite as “an organism that lives on or in a host organism and gets its food from or at the expense of its host.” Gross, right? The sad truth is that we live in a world filled with bacteria and creepy crawlies, and our dogs will inevitably get infected with a parasite at some point in their life. The best thing we can do for our canine companions is to recognize the infection signs of dog parasites, treat them accordingly, and do our best to prevent another infection in the future. 

Types of Dog Parasites

There are 3 main types of dog parasites: intestinal, internal, and external. Here are some of the most common dog parasites you need to know.

1. Intestinal Dog Parasites

Intestinal parasites live in your dog’s digestive system. 


Roundworms are one of the most common dog parasites, and they most often infect puppies. These parasites look like strips of spaghetti (gag) and are usually a few inches long. You might be able to see them in your puppy’s feces, but your veterinarian can confirm. Symptoms of roundworm infection include coughing, vomiting, diarrhea, and weight loss. Roundworms can infect other dogs and even children and are treated with a dewormer.


Hookworms live inside your dog’s digestive system and are pretty common in puppies. Puppies ingest the hookworms while nursing and adult dogs get them from swallowing eggs or from the hookworm burrowing into their skin (ew!). These hookworm larvae live in soil and are ingested when a dog comes into contact with them via grooming or eating grass, poop, etc. Hookworms attach to your dog’s intestinal wall and feed on their blood. The blood loss hookworms cause can have serious health effects, especially on young puppies or small dogs.

An infected dog can also give hookworms to other dogs via nursing or infected feces. Diarrhea and weight loss are common symptoms, and your veterinarian can detect hookworms in a stool sample using a microscope. 


Tapeworms are ingested by our dogs, usually via an adult flea acting as a host. When our dogs have fleas and try to itch, they might swallow the flea in the process. If that flea is hosting tapeworm eggs, your dog now has a ride-along parasite. Tapeworms cause weight loss and diarrhea, and you can often see segments of the tapeworm, resembling grains of rice, in your dog’s stool or around their anus.

The best way to protect your dog from tapeworms is to keep them on flea medication and away from garbage and dead animals. Should they become infected, your veterinarian will give your dog a dewormer medication.

2. Internal Dog Parasites

Internal dog parasites live inside a dog like intestinal parasites but in locations other than the digestive system.


Heartworm enters your dog’s system through the bite of a mosquito infected with heartworm. These tiny worms enter your dog’s heart (hence the name), where they can grow up to one foot in length. These heartworms effectively clog the dog’s arteries, forcing their hearts to work much harder. This issue, if untreated, eventually leads to heart failure.

Signs of heartworm infection include reduced appetite, fatigue after even mild exercise, and a persistent cough. Veterinarians can detect the presence of heartworms before your dog shows any signs, so they often perform heartworm tests at routine checkup visits. To prevent heartworm infections, keep your dog on regular doses of heartworm preventative. 

3. External Parasites

External parasites live in or on your dog’s skin and do not enter their bodies.


Everyone who’s ever had a dog has likely had a run-in with a flea or two. Even when we keep our dogs’ on their flea medication, one or two might make their way into our home before dying the glorious death they deserve. Fleas are tiny, wingless insects that feed on the blood of mammals. Even worse, they make their hosts, our dogs included, so itchy they can scratch their skin raw. As mentioned above, ingested fleas can also carry tapeworm eggs into our dogs’ digestive systems.

Dog, Hovawart, Scratch, Animal, Pet, Movement, Black

If you notice fleas on your dog, it’s best to act as quickly as possible to prevent an infestation of your entire home. If you notice tiny black, sesame seed-sized insects crawling around on your dog, there’s a good chance they have fleas. You might also see little black specks called “flea dirt.” You can treat fleas with medicated shampoo or oral medicine, but a preventative method is the best way to treat fleas. 

Read more about How To Prevent and Get Rid of Fleas on Dogs.


Ticks ingest dogs’ blood, but their actual danger comes from the other diseases they can carry and transfer. These dog parasites cause canine tick-borne disease, Rocky Mountain Spotted Fever, and Lyme Disease, to name a few. There are 800 species of ticks, and they feed on mammals, reptiles, and birds.

Dog, Flea, Scratch, Young, Flea, Flea

Check your dog (and yourself!) for ticks anytime they spend time outside and remove them immediately. You can purchase a tick key for this job, but you can also numb the tick with rubbing alcohol and remove it carefully with tweezers. Kill the tick by placing it in a container of alcohol. Many flea preventatives include tick preventative, and we highly recommend keeping your dog on a flea and tick preventative medication. 

Keep Your Dog Safe From Dog Parasites

If dog parasites teach us anything, the best defense is a good offense; we can prevent most parasitic infections with regular medication or by restricting our dogs’ access to trash, dead animals, feces, etc. Regular trips to our veterinarians for annual physicals and tests are another effective way to combat dog parasites and catch any possible infections early on.

shallow focus photography of white shih tzu puppy running on the grass

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