Intestinal parasites in dogs and cats are more common than most pet owners expect. A new study published in Frontiers in Veterinary Science screened 708 dogs and cats in Portugal and found that roughly 4 in 10 animals were carrying gut parasites — even when they appeared completely healthy. The findings serve as a strong reminder that a pet who looks perfectly fine on the outside may still need preventive care on the inside.
Healthy-Looking Pets Can Still Carry Gut Parasites
This is the key message from the research: gut parasites are often invisible. Many infected animals show no clear signs of illness at all. You might never know your dog or cat had parasites without a fecal test — a simple lab check of a stool sample that your vet can run at a routine wellness visit.
The study examined intestinal parasite prevalence across 363 dogs and 345 cats. The results were striking: 41.6% of dogs and 42.6% of cats tested positive for intestinal parasites. That works out to roughly 4 in 10 animals across both species.
How the Researchers Checked for Parasites
The study was a cross-sectional survey — meaning the team took a single snapshot of a large group of animals at one point in time to see how many were infected. Think of it like a wide photo rather than a video: it shows you who has parasites right now, not how infections change over time.
The researchers screened a mix of dogs and cats across Portugal and tested fecal samples — small stool samples collected from each animal — in a lab to detect intestinal parasites.
This type of survey is well suited for measuring how common a condition is in a real-world population. It can also identify which groups of animals appear to be more often affected.
What the Numbers Show
Parasites Were Found in About 4 in 10 Animals
The main finding is clear:
- 41.6% of dogs tested positive for intestinal parasites
- 42.6% of cats tested positive
Both figures are close to that “4 in 10” mark. If you lined up ten dogs and ten cats at random, about four in each group would likely be carrying some kind of gut parasite.
This rate may come as a surprise to owners who believe their pets are protected because they eat well, live mostly indoors, or seem energetic and healthy. The data suggest that gut parasites are widespread — and that outward health is not a reliable sign that a pet is parasite-free.
Living Conditions Are Associated with Parasite Exposure
The researchers also found that living conditions are linked to how likely a pet is to have intestinal parasites. Where and how a pet lives — including contact with other animals, access to outdoor spaces, and the regularity of preventive care — may be connected to their parasite risk.
Pets that spend time outdoors, live alongside many other animals, or have less consistent parasite prevention may be more often exposed through contaminated soil, water, feces, or prey animals.
What This Means If You Have a Dog or Cat
Regular Fecal Testing Is the Most Reliable Detection Tool
This study reinforces a simple but important point: don’t wait for signs of illness before checking for parasites. A fecal test — where your vet analyzes a fresh stool sample in a lab — is the most dependable way to find gut parasites early. It’s typically quick and affordable, and it can be done as part of a routine wellness checkup.
Most veterinary guidelines suggest testing once or twice a year for adult pets, and more often for young animals, pets that go outdoors regularly, or those in multi-pet households.
Ask Your Vet About the Right Preventive Medication
Many pet owners give their dogs and cats monthly heartworm preventives, but not all of those medications protect against intestinal parasites. It’s worth asking your vet whether your pet’s current preventive covers the common gut parasites in your region — including roundworms, hookworms, and other worms.
The right plan depends on where you live, your pet’s lifestyle, and their age. Your vet is the best person to help you choose.
Indoor Pets Are Not Automatically Safe
It’s tempting to assume that a cat who never goes outside or a dog who rarely leaves the yard is protected. But gut parasites can reach pets in a variety of ways: through contaminated soil tracked indoors, contact with other infected animals, hunting insects or rodents, or even on shoes and hands.
Some intestinal parasites — especially roundworms and hookworms — can also affect people, particularly young children. This is called zoonotic transmission (meaning a germ can pass between animals and humans). Routine deworming of pets is one way to lower that shared household risk.
Know the Signs — But Don’t Rely on Them Alone
One of the most useful lessons from this study is that pets can carry parasites without appearing sick. When symptoms do appear, they may include:
- Soft or runny stools
- Visible worms or worm segments in feces or near the rear end
- Weight loss despite eating normally
- A bloated belly, especially in young animals
- Dull coat or low energy
- Vomiting in some animals
Even so, many infected pets show none of these signs. That is exactly why routine screening is so valuable — it catches infections that would otherwise go unnoticed.
Signs That Warrant a Vet Visit
Contact your veterinarian if:
- You see anything that looks like worms in your pet’s stool or around their rear
- Your pet has unexplained weight loss, persistent diarrhea, or a bloated belly
- Your pet hasn’t had a fecal check in the past year
- You’re not sure whether your pet’s current preventive medication covers intestinal worms
Young puppies and kittens deserve special attention — their immune systems are still developing, and intestinal parasites can affect them more seriously than adult pets.
Study Limitations Worth Knowing
As a cross-sectional study conducted in Portugal, the results show one snapshot of one population at one moment in time. The findings may not translate directly to pets in other countries or regions, where different parasite species, climates, and prevention routines could shift the numbers.
The study design also doesn’t track changes over time, so it cannot tell us whether infection rates are rising, falling, or staying the same. Longer-term research across multiple regions would help paint a fuller picture of how parasite exposure varies with geography and lifestyle.
Four in Ten Pets Tested Positive — What to Do Next
A new study found intestinal parasites in 41.6% of dogs and 42.6% of cats screened in Portugal — roughly 4 in 10 animals across both species. The research also found that living conditions are linked to parasite exposure, and that fecal screening remains important even when pets appear healthy.
If your dog or cat hasn’t had a fecal test recently, this study is a good reason to bring it up at your next vet visit. Regular testing, appropriate preventive medications, and basic hygiene are among the most practical steps you can take to help keep your pet — and your household — protected from gut parasites.
This article summarizes peer-reviewed research for educational purposes. Always consult with your veterinarian for personalized advice about your pet’s health and behavior.
