GI Parasites – Screen. Treat. Prevent.

Tue Jan 23, 2024

What you need to know about GI Parasites?

The word “parasite” has negative connotations for a reason. Not only can gastrointestinal (GI) parasites pose a severe threat to your pet’s health, but they can also be zoonotic, spreading from pets to humans in some cases. The CDC describes 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. Parasites can live on the outside (think fleas and ticks) of the body, or on the inside (think worms that live in the stomach, intestines, and other organs).

In this blog, we’ll share important information every pet parent should know about the most common GI parasites that impact dogs and cats in the US: roundworm, hookworm, whipworm, tapeworm, giardia, and coccidia.

We’ll discuss how to detect, treat, and prevent GI parasites — often referred to collectively as “worms” — and why this is as important as keeping up to date with vaccines, preventing flea and tick infestations, and keeping the threat of heartworm disease away.

Roundworm. Source: The Companion Animal Parasite Council (CAPC)


Why are GI parasites such a problem?

For one thing, they are good at infecting even well cared for domestic dogs and cats. “Dogs will test positive for GI parasites at least three times during their lifetime,” says Dr. Eran Shemer, co-owner of Tolland Veterinary Hospital. “Not a day goes by that we don’t find parasites in a screening for a dog, cat, or both,” he notes.

GI parasites are not only very common but also represent a serious health threat. They can cause weight loss, chronic diarrhea, poor coat, skin issues, bloody feces, dehydration, and can even impact immune function. And because intestinal parasites cause harm by preventing the host’s ability to absorb nutrients through the digestive tract, an infection can cause overall weakness and failure to grow and thrive. Severe GI parasitic infections can cause damage to tissue and organs over time.

“For example, Whipworms can cause Pseudo-Addison disease in dogs,” Dr. Shemer says, adding that this severe endocrine condition is treatable once the parasites have been cleared. “It’s always best to make prevention and screening part of your pet’s regular care regimen and to treat a GI parasite infection early, before it causes serious health problems.”

Parasites live everywhere, so pets can pick them up easily. They are incredibly persistent and engineered by nature to survive by infecting a host animal. “A strong immune system isn’t enough to prevent a parasitic infection,” Dr. Shemer says. “If a pet is exposed to parasites, that pet will become infected. Period.”

Even more challenging, pets can appear healthy but still have GI parasites, which they can transmit to other pets. That’s why it’s so important to screen for parasites at your fur baby’s annual wellness exam.

Source: The Companion Animal Parasite Council (CAPC)


What about over-the-counter de-wormers?

“Sometimes well-intentioned people treat pets with OTC de-wormers or other products that tend to have poor efficacy, and/or they don’t follow the correct protocol for using de-worming medication,” Dr. Shemer says. “They may be able to clear part of the infection, but not all of it. We have found hookworms, whipworms, giardia, and tapeworms in the stool of rescue dogs even after these dogs had allegedly been de-wormed multiple times.”

Parasites can be tenacious, which is why Tolland Veterinary Hospital strongly recommends rechecking a pet’s stool after de-worming to ensure that the parasites have been eliminated.


One type of GI parasite is spreading in our area

Thanks to better education, screening, and prevention tools, the prevalence of most GI parasites has declined in our area over the past ten years. The Companion Animal Parasite Council’s website offers insightful parasite prevalence maps that allow filtering by parasite type, pet species, state, and county to see the current rate of positive tests and compare it to previous years.

One exception to the reduced infection rate is the prevalence of giardia in dogs. The rate of positive test results for this parasite has increased from 1 in 20 positive tests (5.81%) in 2013 to 1 in 12 positive tests (7.54%) in 2023.

Why is this particular parasite gaining traction? One possibility is that it’s common for a dog to be infected and not show symptoms. A seemingly healthy dog could be spreading the parasite without anyone suspecting. Giardia is also highly contagious, and the cysts that spread the infection can linger for months in the environment, even in cold temperatures.


Connecticut’s Positive Test Giardia Test Rate for Dogs in 2013

Connecticut’s Positive Test Giardia Test Rate for Dogs in 2013 Source: The Companion Animal Parasite Council (CAPC)

Click here to go to the interactive map.

Giardia is no joke. It can cause sudden, acute diarrhea, soft watery stools with a foul odor, and abdominal discomfort. It is also among the GI parasites that can spread from pets to humans. Fortunately, it can be treated with a de-worming medication and/or an antibiotic, and recovery may include support with a special diet. A thorough bath following treatment is recommended to ensure there are no giardia cysts remaining on the skin or fur. Steam cleaning and disinfectants are effective at killing giardia in the home, and direct sunlight kills the parasite outdoors.

Like giardia, coccidia is a single-celled parasite that can cause severe diarrhea. It can be life- threatening to puppies and kittens, which is why puppies and kittens should be screened and treated as soon as possible, especially if they show symptoms.


Connecticut’s Positive Test Giardia Test Rate for Dogs in 2023

Connecticut’s Positive Test Giardia Test Rate for Dogs in 2023 Source: The Companion Animal Parasite Council (CAPC)

Click here to go to the interactive map.


Giardia under the microscope

Giardia. Source: CDC


My home and yard are clean. How could my pet become infected?

Parasites and their eggs are microscopic, so an area that appears clean may still harbor just enough contamination for your pet to become infected. And some parasites can be transmitted before or immediately after birth.

Dogs and cats get GI parasites by ingesting the parasite or its egg in contaminated food or water, or by coming into direct contact with the parasite outdoors in the yard, dog park, or on a walking trail. All it takes is for the dog or cat to lick a surface that has invisible traces of fecal matter from a wild or domestic animal infected with the parasite. Puppies and kittens can even get GI parasites from their mother’s milk or in the womb before they are born.

Transmission can also occur through an intermediate host. For example, cats can become infected with tapeworms by ingesting infected fleas while grooming themselves or by eating infected rodents. Therefore, it’s important to control fleas and rodent populations your cat may encounter, and to try to prevent your cat from hunting.

Tapeworm. Source: Merck Veterinary Manual


Danger to humans

Going from the unsavory to the somewhat alarming, consider this: roundworms, hookworms, and giardia are zoonotic, which means they can be passed from pets to humans.

Roundworm eggs and larvae are passed in animal feces, which can contaminate back yards, parks, or playgrounds – or basically anywhere animals have access. These eggs and larvae can live in the environment for long periods of time, which means a prolonged risk of exposure to humans (and their pets) exists even if the area appears clean and green.

Humans can become infected with roundworms when contaminated soil or plants are accidentally ingested (think kids on playgrounds, at the beach, or simply playing in their own backyard). A roundworm infection in humans can cause tissue and nerve damage, even blindness.

Hookworms can penetrate our skin, so we can become infected with this parasite when we walk barefoot or sit on contaminated soil or sand. Hookworms cause cutaneous larval migrans, an inflammatory condition that leaves red, itchy tracks in human skin. And one type of hookworm can cause more serious damage to human intestines and other organs.

Hookworm. Source: The Companion Animal Parasite Council (CAPC)

As we mentioned above, giardia spreads easily and can make people sick with an intestinal infection called giardiasis that causes stomach cramps, bloating, nausea, and watery diarrhea.

Bottom line: GI parasites are bad news. You don’t want your pet to become infected. But if they do somehow pick up an intestinal parasite, you want to know right away and take steps to deal with the situation.


The importance of screening & prevention

Fortunately, there is some encouraging news. “It’s so easy to screen for GI parasites. We recommend screening once a year,” says Dr. Shemer. That icky little baggie you’re asked to bring with you to your pet’s checkup is “arguably the most important part of the annual wellness exam. It’s more likely that a pet will contract health-damaging parasites than one of the viral diseases we vaccinate for.” He quickly adds, “We aren’t suggesting that you stop vaccinating, though, as this is also very important. And, as is the case with the rabies vaccine, may be required by law. Just don’t forget to bring the stool sample to your pet’s wellness exam!”

Prevention is also easier than you might think. Heartguard, available for both cats and dogs, is a chewable, monthly medication that prevents many internal parasites, including heartworm, hookworm, and roundworm.

Dr. Shemer notes that if a pet has already become infected and is in the process of being treated, steps can be taken at home to improve hygiene and reduce the chance of spreading the infection to humans or other pets. This includes making sure the area under the pet’s tail is kept clean to clear any parasite eggs. Puppies are especially vulnerable to contracting giardia infestations, which can take 6 to 7 months to clear.


Here are some things you can do to protect your pet (and yourself!) from GI parasites:

• Make sure you bring a fresh stool sample to your pet’s annual wellness exam for screening.
• Have kittens and puppies screened for parasites as soon as possible.
• Keep your pet’s area clean and free of feces at home.
• Keep litterboxes clean.
• Promptly bag and throw away any feces.
• If your pet is being treated for an infection, avoid contact with other pets.
• Wipe an infected pet’s bottom after defecation.
• Prevent cats from hunting rodents.
• Always provide fresh, clean water for your pet.
• Avoid raw food diets.
• Thoroughly clean pet toys on a regular basis.
• Wash your hands with soap and water after playing with pets, cleaning up after them, or spending time outside.
• Keep children’s sand boxes covered.


Fast facts about common GI parasites found in cats and dogs
Giardia Single-celled parasite, can be contracted from ingesting food or water contaminated with feces. Lives in the small intestine and causes diarrhea. Especially dangerous for kittens and puppies. Note: chlorinated public water does not kill the cysts that, when ingested, cause an infection.
Coccidia Single-celled, lives in the wall of intestine. Causes diarrhea and can be severe and life-threatening to puppies and kittens. Transmitted when host ingests contaminated soil or feces, or infected rodents.
Roundworm Most common GI parasite in cats. Adult roundworms can be 3 to 5 inches long. Transmitted when cats eat eggs or infected rodents. Kittens can become infected through mother’s milk. Roundworm can cause intestinal blockage (life-threatening).
Hookworm Less than ½ inch long, thread-like. Larvae can penetrate the skin or be ingested then migrate to the lungs or intestines. Can cause anemia.
Whipworm Uncommon in cats in the US. Whipworms can contaminate the environment indefinitely, and infected animals require treatment for life with a medication called Interceptor. Whipworms live in the small intestine and can live as long as the host.
Tapeworm Adult parasite lives in the small intestine. Segments can be seen around the rectum or in stool and can resemble grains of rice or sesame seeds. Some kinds of tapeworms can cause disease in humans if accidentally ingested.

If you have questions about screening, treatment, or prevention measures related to GI parasites, contact us and we’ll do our best to help.


USDA Flyer about GI parasites in dogs:,infections%2C%20but%20reinfection%20is%20common.

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