(© Saklakova – stock.adobe.com)
In a nutshell
- Park entrances have the highest concentration of Toxocara parasite eggs, followed by playgrounds, posing a health risk to humans through accidental contact with contaminated soil.
- Dogs are the primary source of this contamination (92% of identified eggs), with many owners reporting their pets often defecate shortly after arriving at parks.
- Effective interventions should focus on park entrances, as signage alone doesn’t prevent contamination—researchers observed dog owners bringing puppies into fenced “no dogs allowed” playgrounds.
DUBLIN — Most of us head to local parks thinking about relaxation, exercise, or family time—not invisible parasitic eggs that might be lurking in the soil. Yet a new study reveals something park-goers should know: those entrances where you first step into green spaces are actually hotspots for parasitic contamination.
Researchers from Trinity College Dublin and Queen’s University Belfast found that park entrances consistently contained the highest concentration of Toxocara eggs—parasites that can cause serious health problems in humans. Playgrounds ranked second in contamination levels, despite most having fences and “no dogs allowed” signs.
These findings, published in PLOS Neglected Tropical Diseases, matter because when we accidentally come into contact with contaminated soil, we risk exposure to parasites that can cause difficult-to-diagnose illnesses. What makes this risk easy to overlook is that symptoms often don’t stand out—they can be mild or mistaken for other conditions.
Roundworm Larvae Found In Soil Samples
The research team, led by Jason D. Keegan, examined 12 Dublin parks using a systematic approach they hope will become standard practice for similar studies worldwide. They developed a repeatable sampling strategy using geographic information system (GIS) software to ensure consistent data collection across all parks.
Results show that 4.66% of the 836 soil samples contained Toxocara eggs, with levels varying significantly between parks. Two parks had notably higher contamination than others. What’s concerning is that over 92% of the eggs they found contained moving larvae, meaning they were potentially infectious to humans.
“Toxocara canis and Toxocara cati, the common roundworms of dogs and cats respectively, are commonly found in the soil of public parks,” the researchers explained in their paper. These parasites don’t just affect pets—they’re zoonotic, meaning they can jump from animals to humans.
Recent analyses show that about 11% of dogs and 17% of cats worldwide are infected with these roundworms. Even more concerning is that up to 19% of people globally have been exposed to Toxocara, based on blood test data. This makes it one of the most widespread parasitic infections in the world, yet many people have never heard of it.
Human infection can lead to toxocariasis, which can affect various organs including the eyes. These conditions can be particularly difficult to diagnose because symptoms often aren’t specific enough to point doctors in the right direction.
Dogs Are The Primary Park Poop Parasite Problem
When infected dogs or cats defecate in parks, they release eggs into the environment. Under the right conditions of temperature and humidity, these eggs develop and become infectious. The Dublin study confirmed that dogs were the main culprits, with 36 out of 39 successfully tested eggs identified as Toxocara canis (dog roundworm).
Many dog owners reported that their pets often defecate soon after arriving at parks, explaining the concentration of eggs around entrances. More puzzling was the playground contamination, as most were fenced with signs prohibiting dogs. Researchers actually witnessed dog owners bringing puppies into these restricted areas multiple times during their study, suggesting that signage alone doesn’t solve the problem.
Environmental factors also influenced where eggs were found. More eggs appeared in soil samples with plant cover, possibly because vegetation maintains suitable moisture levels and provides shade from direct sunlight, protecting the eggs. The team also found more eggs in spots they subjectively judged as places they wouldn’t choose to sit—suggesting that unappealing areas might naturally deter people from direct contact with more contaminated soil.
The Dublin contamination levels (4.66% of samples positive) were lower than those found in previous studies from the early 1990s (13%), possibly reflecting a significant reduction in stray dog numbers in Ireland over the past two decades. In 2002, over 21,000 dogs were euthanized in Irish pounds, compared to just 168 in 2021—a dramatic decrease that may have helped reduce environmental contamination.
No Fouls, No Harm
Study authors suggest concentrating preventive efforts on park entrances to reduce risks of disease transmission. They note that despite dog fouling being one of the most complained about issues in public spaces, evidence for effective interventions is surprisingly thin. Dog fouling refers to when dogs defecate in public places and their owners don’t clean it up.
Some successful approaches have reduced dog fouling by up to 60%. These include campaigns involving schoolchildren creating posters and stencils to discourage the problem, using posters with eyes that appear to “watch” park users (which also glow in the dark), and marking dog waste with bright pink environmentally friendly spray paint to raise awareness.
You might want think twice next time you step foot in your favorite local parks, especially near entrances. If you’re a dog owner, always pick up what your pet leaves behind—you’re not just keeping the park pleasant for others, you’re helping prevent the spread of parasites that can cause real health problems.
Paper Summary
Methodology
The researchers created a straightforward but thorough approach to studying soil contamination in parks. They started by using mapping software to draw boundaries around specific areas in parks: entrances, playgrounds, playing field edges, and sitting areas. Within these boundaries, they placed random sampling points at least 2 meters apart. Using smartphones with GPS, they found these exact spots and collected soil samples with a garden tool called a bulb planter, which removed consistent soil plugs about 2-5 cm deep. Each location’s sample combined five smaller samples to create one 250g composite. They noted details like soil temperature, moisture, plant cover, and whether they’d sit in that spot. Back in the lab, they dried the soil, filtered it through a fine mesh, and used a special technique to separate any parasite eggs from the soil. They photographed any eggs found and used DNA testing to determine whether they came from dogs or cats. The team also validated their method by testing how many eggs they could recover from soil samples with known numbers of eggs added.
Results
The team collected 836 soil samples from 12 Dublin parks. Of these, 39 samples (4.66%) contained Toxocara eggs. Different parks had widely varying contamination levels, from completely clean to nearly a quarter of samples containing eggs. In total, they found 94 eggs across all positive samples, with an average of 2.41 eggs per contaminated sample. The most concerning finding was that 92.55% of eggs contained moving larvae, meaning they were potentially infectious. Park entrances had the highest concentration of eggs, followed by playgrounds. Playing fields and sitting areas had significantly fewer eggs. When examined using DNA techniques, 36 out of 39 successfully tested eggs were from dogs (Toxocara canis), with only three from cats (Toxocara cati). This confirms dogs as the main contamination source in these parks. The researchers also tested 49 fresh fecal samples they found, but only one (2%) contained Toxocara eggs, suggesting most eggs in the soil had persisted long after the waste itself had broken down.
Limitations
The researchers acknowledge several constraints in their study. Their egg recovery method had a 49% success rate, meaning they likely detected only half the eggs actually present. The playground sampling differed slightly from other areas due to varying designs and surfaces. The relationship between vegetation and egg presence might be influenced by unmeasured factors. Their judgment about whether they would sit in certain locations might reflect visual cues associated with contamination rather than actual egg presence. While they identified 39 eggs to species level, 16 eggs were lost during processing, and DNA analysis failed for several others, potentially skewing the species distribution results. Finally, the sampling occurred over a specific time period and might not reflect seasonal variations in contamination levels.
Funding and Disclosures
This research received funding from The Irish Research Council’s Postdoctoral Fellowship program (GOIPD/2020/510 to JDK and CVH). The funders weren’t involved in study design, data collection, analysis, publication decisions, or manuscript preparation. The authors declared no competing interests that might have influenced their work or its interpretation.
Publication Information
This study, “Park entrances, commonly contaminated with infective Toxocara canis eggs, present a risk of zoonotic infection and an opportunity for focused intervention,” appeared in PLOS Neglected Tropical Diseases on March 27, 2025. The research team included Jason D. Keegan from Trinity College Dublin’s Parasitology Research Group, Department of Zoology, working with colleagues from Queen’s University Belfast’s School of Biological Sciences. The article is freely available as an open access publication under the Creative Commons Attribution License, allowing unrestricted use and sharing with proper attribution to the original authors and source.
