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Intestinal Parasites 101: What You Need to Know as a Responsible Pet Owner

Why does my puppy have a potbelly?
By Agnes Molek, November 2021, Updated December 2021
dog with parasites

If you’re a new pet owner and you’ve noticed something strange (maybe even wiggling) in your pup’s poop, been concerned about your dog’s potbelly, or reached out to your dog’s veterinarian about bloody diarrhea, you aren’t alone. The majority of the time, the answer to these questions points to a group of nutrient-depleting and blood-sucking culprits: intestinal parasites.

Intestinal parasites can range in size, shape, route of transmission, and how they affect the host. However, not all pet owners, especially those who just got a new puppy or kitten for the first time, are well informed about parasitic infections. If you are that new pet owner, congratulations on your new family member! Here is some important information about intestinal parasites and your pup’s (or cat’s) pooping habits.

What is a Parasite?

In general, a parasite is an organism that feeds and lives on (or in) a host animal (such as a dog or a cat). In the case of intestinal parasites, the host is usually harmed in one way or another by the parasite. In some cases, parasites can even be fatal. As the name suggests, intestinal parasites, in both dogs and cats, can be found somewhere along the pet’s gastrointestinal tract, usually being the stomach or small and large intestines. In the case of puppies and kittens, they are more likely to have more severe symptoms because things like blood and nutrients are being taken away during a crucial time of growth and development.

But how do pets get these parasites? There isn’t a simple answer to that question. There are different routes of transmission and infection for the different kinds of intestinal parasites. Your pet may get a parasite by doing something as simple as standing on grass that has parasitic larvae on it or through a flea bite. A great majority of puppies and kittens are actually born with at least one intestinal parasite.


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How do puppies and kittens get parasites when they haven’t explored the outdoors yet? It all goes back to mom. If a pregnant mom gets infected with an intestinal parasite, the parasites may transmit while they are still in utero. Another possible route from mom to puppies is during nursing, where the parasite is transmitted through mom’s milk. But let’s say that while pregnant, the puppy’s mom tested negative for any and all possible intestinal parasites. However, a few months ago, she tested positive and completed the entire deworming process. During the initial infection, it is possible that some of the parasitic larvae migrated into muscle tissues where they laid dormant until the perfect opportunity, in this case, pregnancy, arose.

Common Intestinal Parasites in Dogs and Cats

Now that you’re aware of the problem, it’s time to dive into the nitty-gritty of intestinal parasites. Below you’ll find a list of the most common intestinal parasites your pet can get, how they are transmitted, symptoms to look for, and different treatment options and preventative measures that should be considered when owning a dog, cat, or both!


Ancylostoma caninum (Canine hookworm), Ancylostoma tubaeforme (Feline hookworm)

There are several ways a pet might be infected with hookworm, including: through ingestion of contaminated fecal matter or soil, when a parasite larvae burrows through the skin when standing or laying on contaminated ground, prenatal infection (from mom to offspring in utero), and transmammary infection (from mom to offspring while nursing). Important: it should be noted that hookworms can be transmitted to humans.

Hookworm Symptoms:

  • Dry or dull haircoat
  • Anemia
  • Pale gums
  • Lethargy
  • Bloody diarrhea
  • Significant weight loss or inability to gain weight

Treatment: Treatment for hookworms is usually oral dewormers (anthelmintics), which only kill adult worms. Infected dogs or cats have to repeat treatment about two to four weeks after the first treatment.


Toxocara canis (Canine hookworm), Toxocara cati (Feline hookworm), Toxocara leonina (infectious to Canine and Feline)

Pets can get infected with roundworms by sniffing or licking infected feces from another animal. Dogs and cats can also get roundworms if they ingest a paratenic host (accidental host), like rodents, earthworms, and birds. Similar to hookworm, transmission is possible through both prenatal and transmammary infection. Roundworms can be transmitted to humans too.

Roundworm Symptoms:

  • “Spaghetti” in pet’s fecal sample or vomit
  • Recurrent diarrhea
  • Potbelly (puppies)
  • Lethargy
  • Stunted growth (puppies)

Treatment: When treating Roundworms, oral dewormers (anthelmintics) are used. Oral dewormers only kill adult worms. Infected dogs or cats have to be retreated about two to four weeks after the first treatment.


Giardia duodenalis (can be found in both Canines and Felines)

A dog or cat may be infected by giardia by drinking water that has been contaminated by feces from an infected animal or eating something contaminated by infected feces like grass or dirt. Not all pets show symptoms of giardia.

Giardia Symptoms:

  • Diarrhea
  • Lethargy
  • Dehydration
  • Weight loss
  • Inability to gain weight

Treatment: To treat giardia in pets, doctors will typically prescribe a combination of fenbendazole (dewormer) and metronidazole (antibiotic) for about ten days. After that, the pet’s feces should be retested two to four weeks after finishing the medication. 


Trichuris vulpis (Canine whipworm), Trichuris serrata (Feline whipworm)

Pets may be infected with Whipworm when ingesting eggs from a contaminated piece of soil, grass, or feces.

Whipworm Symptoms:

  • Chronic watery, bloody diarrhea
  • Significant weight loss
  • General debilitation (inability to conserve salt, leading to chronic dehydration)

Treatment: Whipworms rarely pass eggs, so fecal samples often come back false negative. The most common dewormers used to treat whipworms are fenbendazole and febantel.


Dipylidium caninum (Canine and Feline tapeworm), Taenia tapeworm species, Echinococcus hookworm species

Pets can be infected with tapeworm if they eat an infected flea (Dipylidium caninum), undercooked or raw meats (various Taenia species), or contaminated feces (various Echinococcus species). Unfortunately, some forms of the Taenia and Echinococcus species of tapeworms can be transmitted to humans.

Tapeworm Symptoms:

  • Moving “rice-like” segments found around pet’s rectum or in their feces
  • Weight loss
  • Diarrhea
  • Lethargy
  • Distended abdomen

Treatment: Tapeworms often don’t show up on fecal screenings but can be seen without a microscope (wiggling stuff in your pup’s poop). Treatment of tapeworm in pets consists of one or two rounds of praziquantel dewormer, which generally covers all tapeworms types. Alternatively, pets may be treated with fenbendazole, which does not kill Dipylidium caninum.

Parasite Prevention:

If all this information has you thinking about the last time you had your pet tested for intestinal parasites, this is your sign to get your pet’s poop checked. Intestinal parasites can be very scary—while treatment is usually easier than you might think—prevention is always best.

  • Make sure your new pup or kitten is up-to-date on their immunizations.
  • Pick up your pet’s poop to prevent the spread, transmission, and reinfection of the parasite.
  • Practice good hygiene, like washing your hands after picking up feces. Especially those families with younger children.
  • Make sure your pet has clean water accessible at all times to avoid drinking from puddles.
  • Limit exposure to areas where dog feces will be.
  • Many heartworm preventatives contain deworming medication that will kill intestinal parasites.

If your pet is experiencing any of the symptoms mentioned, do your pup and yourself a favor and get their poop tested for possible parasites. It’s easy! To test their poop, simply bring in the freshest poop sample you can find, and the clinic staff will do the rest. Veterinarians typically will have results generally within the next 24-48 hours.

Photo: AdobeStock

Agnes Molek is a graduate student working on her Master’s degree in Biology through Chicago Zoological Society’s Brookfield Zoo connection to Miami University Oxford. She has a Bachelor’s in Biology with a minor in Psychology. She is a veterinary technician at a small animal and exotic veterinary clinic and has two very energetic hounds named Kona and Kaiser.