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Perils of pet poop – so much more than just unsightly and smelly, it can spread disease

a sign on a fence warns 'Pet waste transmits disease' with dog park in background
Responsible pet owners are on diligent poop patrol. Hannah Sussman, CC BY-ND

Have you ever been out on a walk and as you take that next step, you feel the slippery squish of poop under your foot?

It’s not just gross. Beyond the mess and the smell, it’s potentially infectious. That’s why signs reminding pet owners to “curb your dog” and scoop their poop have been joined in some places by posted warnings that pet waste can spread disease.

As a small-animal primary care veterinarian, I deal with the diseases of dog and cat poop on a daily basis. Feces represent potential zoonotic hazards, meaning they can transmit disease from the animals to people.

The reality is that waste left to wash into the soil, whether in a neighborhood, trail or dog park, can spread life-threatening parasites not just among dogs and cats, but also to wild animals and people of all ages. A 2020 study found intestinal parasites in 85% of off-leash dog parks across the United States.

While human diseases caused by soil-transmitted parasites are considered uncommon in the U.S., they infect as many as an estimated billion people worldwide. Signs that remind you to pick up after your pet are not just trying to keep public spaces clean; they’re urging you to help safeguard your community’s health.

bottom of a child's foot showing open lesions by the toes
Parasites can enter your body through broken skin and set up shop, as in this hookworm infection. CDC, CC BY

Abandoned poop’s impact on people

Common dog poop parasites include hookworms, roundworms, coccidia and whipworms. Hookworms and roundworms can thrive in a variety of species, including humans.

Their microscopic larvae can get into your body through small scratches in your skin after contact with contaminated soil or via accidental oral ingestion. Remember that next time you’re outside and wipe sweat from your face with a dirty hand and then lick your lips or take a drink – it’s that simple. After hose or rain water has rinsed contaminated poop into the soil, these parasite eggs can survive and infect for months or years to come.

Once in the human body, both hookworm and roundworm larvae can mature and migrate through the bloodstream into the lungs. From there, coughs help them gain access to the digestive tract of their host, where they leach nutrients by attaching to the intestinal wall. People with healthy immune systems may show no clinical signs of infection, but in sufficient quantities these parasites can lead to anemia and malnourishment. They can even cause an intestinal obstruction which may require surgical intervention, especially in young children.

Additionally, larval stages of roundworms can move into the human eye and, in rare cases, lead to permanent blindness. Hookworms can create a severely itchy condition called cutaneous larva migrans as the larval worm moves just under the skin of its host.

about a dozen little white worms next to a wooden match
Adult hookworms. Agency-Animal-Picture via Getty Images

Once the parasite’s life cycle is complete, it may exit the host’s body as an intact adult worm, which looks like a small piece of cooked spaghetti.

The impact on other animals

Dogs and cats can also develop the same symptoms people do due to parasitic infections. In addition to risks of hookworms and roundworms, pets are also vulnerable to whipworm, giardia and coccidia.

Beyond parasites, unattended poop may also be contaminated with canine or feline viruses, such as parvovirus, distemper virus and canine coronavirus, that can create life-threatening disease in other dogs and cats, especially in adult animals that are unvaccinated and puppies and kittens.

These viruses attack rapidly dividing cells, in particular the intestinal lining and bone marrow, leaving them unable to absorb nutrients appropriately and unable to produce replacement red and white blood cells that help defend against these and other viruses. Vaccination can protect pets.

Many species of local wildlife are within the canid and felid family groups. They, too, are susceptible to many of the same parasites and viruses as pet dogs and cats – while being much less likely to have received the benefit of vaccinations. Coyotes, wolves, foxes, raccoons, minks and bobcats are at risk of contracting parvovirus, coronavirus and distemper.

person dropping a bag of dog poop into bin with dog watching
Be prepared to deal with poop on every walk. Elva Etienne/Moment via Getty Images

Responsible pet poop management

So, wherever your dog or cat relieves himself – at the park, in the woods, on the sidewalk, or even in your yard – pick up that poop but always avoid contact with your skin. It’s safest to use a shovel to place the poop directly into a plastic bag, or put a baggie over your hand to grab the poop and then pull the plastic bag over it. While it’s tempting to leave the “soft-serve” or watery poops behind, these are often the more likely culprits for spreading diseases.

Tie up the bag and make sure to place it in a trash can – not on top – to avoid inadvertent contamination of a neighbor or sanitation worker. Promptly wash your hands, particularly before touching your face or eating or drinking. Hand sanitizers can take care of many viruses on your skin, but they won’t kill parasite eggs.

Other potential sources of poop – and parasite – exposure are the sandbox, beaches and park sand found under and around playgrounds. Sand is comfortable to lounge on, fun to construct into castles, and softens the impact if you fall off a play structure. But cats and other small mammals love to use it as a litter box since it’s easy to dig and absorbs moisture. Covering sandboxes when not in use and closely monitoring your environment at the beach and playground are key steps toward minimizing the risks of exposure for everyone.

By keeping your pets on regular parasite prevention protocols, with annual testing for intestinal parasites and routine removal of fecal material from the environment, you can help to minimize the potential for these diseases among all the mammals in your environment – human, pet and wild.

Key points to remember to avoid parasites and minimize the impact on your ecosystem:

  • Pick waste up and safely throw it out regardless of where your pet poops. Sanitize your hands afterward.
  • Wash your hands before eating or touching your face while gardening or working in the yard.
  • Avoid rinsing poop into the soil. Using rain or a garden hose only removes the visible mess, not the microscopic issues.
  • Make sure sandboxes are covered when not in use.
  • Keep your pets on monthly intestinal parasite deworming schedules.
  • Have your vet test your pet’s poop annually for intestinal parasites.

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