Free-roaming NYC cats carry high Toxocara burden, with young males driving contamination

More than half of free-roaming cats sampled across boroughs in New York, New York, were shedding at least 1 gastrointestinal parasite, with the zoonotic roundworm Toxocara the dominant finding, according to results of a study published in PLoS One. The work adds a hard number to a public health concern that has largely been inferred from soil surveys: The cats appear to be the active biological source of the roundworm eggs contaminating city parks and playgrounds.

Researchers led by Pratap Kafle, DVM, PhD, DACVM (Parasitology), an assistant professor of parasitology at Rowan University's Shreiber School of Veterinary Medicine in Glassboro, New Jersey, opportunistically collected fecal and blood samples from 87 cats captured during a Trap-Neuter-Return (TNR) program run through Long Island University's College of Veterinary Medicine between May and July 2023. Samples were run through centrifugal fecal flotation, coproantigen immunoassays, serology, and polymerase chain reaction (PCR) for a panel of gastrointestinal and vector-borne parasites.

Roundworms lead; hookworms and coccidia follow

Fecal flotation showed that 57.5% of the 87 cats were positive for at least 1 endoparasite. Toxocara spp was by far the most common at 54%, followed by Ancylostoma spp (hookworm) at 13.8% and coccidia at 11.5%. Roughly 1 in 5 cats carried 2 or more species at once, most often a Toxocara-Ancylostoma coinfection.

Coproantigen testing on a 43-cat subset picked up Giardia in 11.6% and Cryptosporidium in a single animal (2.3%), including infections that flotation alone had missed—though confirmatory PCR at the Cornell University Animal Health Diagnostic Center did not amplify DNA for either organism in any sample. Serology on 45 cats found 8.9% seropositive for Toxoplasma gondii antibodies, evidence of prior exposure rather than active oocyst shedding. Notably, no heartworm (Dirofilaria immitis) antigen and no Cytauxzoon felis DNA turned up in any blood sample.

The authors frame the T gondii rate—well below the over 25% reported in some free-roaming populations—as a possible "urban shield" effect, in which city cats, relying on human food sources, hunt fewer intermediate hosts and acquire fewer tissue cysts.

Young males as "super-shedders"

The more actionable finding is about intensity, not just prevalence. Although overall infection rates didn't differ much across demographics, egg-shedding did—dramatically. Male sex was a significant risk factor for Toxocara infection, with roughly 4-fold higher odds than in females. Among infected cats, young cats (under 1 year) shed Toxocara eggs at nearly 9 times the rate of adults, whereas males shed at more than 3 times the rate of females.

The authors describe young males as high-intensity "super-shedders" responsible for a disproportionate share of environmental egg output. Their practical takeaway for TNR programs: targeting broad-spectrum anthelmintics at heavily shedding juveniles and young males during the neuter procedure may remove far more eggs from the environment per treatment than deworming every cat uniformly. They caution that egg counts index environmental contamination potential rather than direct worm burden.

Why it matters in the exam room and beyond

The relevance extends past the colony. The authors connect their findings to prior surveillance that detected Toxocara eggs in 38.5% of New York City playgrounds, with T cati, the feline species, predominating over the canine T canis in that soil. Because Toxocara eggs remain infective in soil for years and survive Northeastern freeze-thaw cycles, and because children are at particular risk through geophagia and hand-to-mouth play, the documented shedding points to a durable transmission risk.

For practitioners, the study reinforces the case for aggressive, early, and repeated deworming of kittens and outdoor-access cats, and for counseling clients on the environmental persistence of roundworm eggs. The hookworm finding carries its own caveat: The eggs of the common feline hookworm A tubaeforme are morphologically indistinguishable from the zoonotic A braziliense, so the true zoonotic share can't be pinned down without molecular speciation.

The authors position TNR programs as an underused surveillance platform—one that could pair population control with parasite monitoring and targeted treatment as a One Health measure.

Reference

Nguyen VL, Gurtowski E, Chen J, Rosen M, Kafle P. Zoonotic endoparasites and Toxoplasma gondii seropositivity in free-roaming cats (Felis catus) from New York City boroughs. PLoS One. 2026;21(7):e0351437. doi:10.1371/journal.pone.0351437