Just last week, I had a frantic call from a client named Emily. She had brought her eight-week-old rescue kitten, Pip, into the clinic because he’d been having some digestive upset. When I asked her to bring a stool sample, she was skeptical. Pip lived exclusively in her apartment, slept on a velvet cat tree, and had never once stepped a paw outside. “How could he possibly have a parasite?” she asked.
Well, when we put Pip’s sample under the microscope, the slide was teeming with roundworm eggs. Emily was horrified, but this scenario happens every single day in my clinic. The parasite world is largely invisible. The eggs they shed in pet feces are microscopic, meaning you can’t see them with the naked eye. Because of this, internal parasites are an unseen danger to both our pets and us.
Meet the “Big Six”
When we talk about intestinal parasites in veterinary medicine, we are usually looking at six primary culprits. According to the,[1] these are the most common internal parasites affecting both cats and dogs:
- Roundworms: These look a bit like spaghetti and are incredibly common in puppies and kittens, who often contract them from their mothers.
- Hookworms: These tiny parasites attach to the intestinal wall and feed on the pet’s blood, which can quickly lead to severe anemia, especially in young animals.
- Whipworms: These reside in the cecum (a pouch at the beginning of the large intestine) and cause chronic, watery diarrhea.
- Tapeworms: Often contracted when a pet swallows a flea, these parasites break off into segments that look like little grains of white rice in your pet’s stool or around their back end.
- Coccidia: Microscopic organisms that cause severe, sometimes bloody diarrhea, particularly in crowded or stressful environments.
- Giardia: A water-borne parasite that lives in the intestines and causes foul-smelling, explosive diarrhea.
The “Indoor Only” Myth and Other Sneaky Vectors
How do indoor pets get parasites?
The biggest misconception I hear in the exam room is that strictly indoor pets are safe from parasites. I completely understand the logic—if you don’t go in the woods, how can you get a tick or a worm? But parasites are excellent hitchhikers. They can easily catch a ride into your living room on the bottom of your shoes, on your clothing, or on the paws of another pet in the household. That is exactly how Emily’s kitten, Pip, was exposed. The eggs were likely tracked into the apartment on Emily’s sneakers.
Pets can also catch these invisible hitchhikers by drinking from puddles or stagnant water, ingesting a rogue flea while grooming themselves, or nosing around in contaminated soil at the local park. Mother dogs and cats can even pass dormant larvae to their offspring through the placenta or their milk.
The Raw Diet Debate
Recently, I’ve had many clients ask me about the parasite risks associated with raw diets. There is an ongoing debate regarding the feeding of raw meat to pets. While some owners swear by the nutritional benefits, opponents—including much of the veterinary community—point to the increased risk of transmitting pathogens. If raw meat is not properly frozen, handled, or sourced, it can be a vehicle for Giardia, Toxoplasma, and even tapeworms. I always redirect my patients to evidence-based, commercially prepared diets that have undergone rigorous safety testing to eliminate these risks.
Finding the Unseen: Diagnosis and Treatment
Because these pests are microscopic, you can’t just look at your dog’s stool and know if they have worms (unless you happen to spot those tapeworm segments). Diagnosis requires a fecal examination. We take a small sample of your pet’s stool, run it through a special solution that makes the parasite eggs float to the top, and look at them under a microscope.
Once we know what we are dealing with, treatment is usually highly effective. However, this brings up another common debate: over-the-counter versus prescription medications. I frequently see owners waste their money on store-bought dewormers. The problem is that these broad-spectrum, over-the-counter options are often ineffective against certain parasites, or they are dosed incorrectly for the pet’s specific weight. Veterinary-grade, prescription dewormers are targeted to the exact parasite we identified under the microscope, ensuring your pet gets exactly what they need safely and effectively.
When Parasites Push Back: A Changing Landscape
I’ll be honest—I’ve changed my mind on a few things over my years in practice. For a long time, if a dog came in with hookworms, we gave a standard dewormer, and that was that. But recent veterinary developments have proven that we can’t rely on the same old playbook anymore.
A growing concern in veterinary medicine is the emergence of drug-resistant parasites. We are now seeing hookworms that have mutated to survive the very medications we’ve used for decades. This makes routine fecal testing incredibly important. If your pet has persistent diarrhea, we can’t just assume a standard dewormer will fix it anymore. We have to identify the specific egg, and sometimes run additional tests to determine which medications will actually work.
Protecting Your Home: The “One Health” Approach
Gastrointestinal parasites aren’t just a pet problem; they are a public health risk. These are zoonotic threats, meaning they can be transmitted from animals to humans. This is why studies, like a widely cited 2018 research paper by Raza et al., have pushed the veterinary field to heavily adopt “One Health” initiatives. This concept recognizes that human health, animal health, and environmental health are deeply interconnected. The risk is particularly high in shelter environments, which are highly susceptible to parasite outbreaks due to high turnover, crowded conditions, and animal stress. The intake protocols at shelters—testing and treating immediately upon arrival—don’t just protect the other animals, they protect the staff and visitors, too.
Multi-layered Prevention Strategies
To keep your pets—and your human family members—safe, we need to rely on a multi-layered approach to prevention. According to resources from [2] and other veterinary experts, a solid parasite prevention plan includes:
- Year-round preventatives: Administering monthly, year-round preventative medications prescribed by your vet. I advocate for pharmaceutical preventatives because the clinical evidence supports their safety and efficacy, whereas holistic methods often fall short when a pet is exposed to a heavy parasite load.
- Maintaining strict hygiene: Wash your hands thoroughly after handling pets, cleaning litter boxes, or doing yard work.
- Prompt waste removal: Quickly cleaning up pet feces in your yard and scooping the litter box daily prevents parasite eggs from maturing and contaminating the environment.
Taking care of our pets means taking care of the environment we share with them. While internal parasites don’t have a conservation status—they are pathogens we actively work to eradicate—our approach to controlling them is inherently tied to environmental stewardship. By picking up after our dogs and keeping our cats’ litter boxes clean, we aren’t just keeping our homes tidy. We are actively preventing soil and water contamination in our communities, protecting local wildlife from devastating parasitic infections, and safeguarding human health. When we manage the invisible hitchhikers in our own backyards, we contribute to a healthier, balanced ecosystem for everyone.
Sources
- American Veterinary Medical Association (AVMA) — avma.org
- Mission Veterinary Hospital — missionvet.com