According to the study authors, more than half of free-roaming cats sampled from New York City neighborhoods harbored at least 1 zoonotic endoparasite capable of infecting humans, with young male cats identified as high-intensity shedders of Toxocara roundworm eggs deposited into shared urban soil.1 The findings, published in PLOS One, underscore the public health risks of unmanaged feline populations in densely populated urban centers and call for integration of parasite surveillance and control into existing Trap-Neuter-Return (TNR) programs.
Feral and free-roaming cat populations are common in urban environments and represent a recognized vector for zoonotic disease transmission. Toxocara spp., the most prevalent roundworm in domestic cats, causes toxocariasis in humans through ingestion of microscopic eggs shed in cat feces and contaminating soil. Clinical presentations include visceral larva migrans, characterized by fever, hepatomegaly, and pulmonary symptoms, and ocular larva migrans, which can cause vision loss. Toxocara eggs are highly environmentally persistent, remaining infective in soil for years and surviving northeastern US freeze-thaw cycles.1
Toxocara prevalence, super-shedder dynamics, and zoonotic risk in NYC free-roaming cats
Frequently Asked Questions
What is toxocariasis and how does it spread to humans?
Toxocariasis is caused by ingestion of microscopic Toxocara eggs shed in cat or dog feces and deposited into soil. Eggs can remain infective for years. Clinical presentations include visceral larva migrans (fever, hepatomegaly, respiratory symptoms) and ocular larva migrans (vision loss).
What did this study find about free-roaming cats in New York City?
57.5% of 87 sampled free-roaming NYC cats harbored at least one zoonotic endoparasite, predominantly Toxocara spp. Young male cats shed Toxocara eggs at dramatically higher rates than other cats, identifying them as super-shedders driving disproportionate environmental contamination.
What are the recommended public health interventions?
The study authors recommend integrating targeted deworming (prioritizing young male cats), environmental decontamination, and public education into existing Trap-Neuter-Return programs as a One Health strategy to reduce zoonotic transmission risk in urban settings.
Researchers from Long Island University College of Veterinary Medicine and Rowan University Shreiber School of Veterinary Medicine examined 87 free-roaming cats enrolled in a New York City TNR program, conducting both fecal egg count analysis and serological testing.1 Of the 87 cats sampled, 57.5% harbored at least 1 zoonotic endoparasite, with approximately 20% showing mixed infections involving more than 1 parasite species.
Toxocara spp. was the dominant parasite, accounting for 54% of infected cats. Ancylostoma spp. (hookworm) were detected in 13.8% of cats. Antibodies to Toxoplasma gondii—indicating prior or current exposure—were detected in 8.9% of serum samples (4 of 45). No Dirofilaria immitis antigen or Cytauxzoon felis DNA was detected in blood samples.1
Egg shedding was highly aggregated, with a minority of cats responsible for a disproportionate share of environmental contamination. Male cats were significantly more likely to be infected with Toxocara (OR 4.36), and both young cats (<1 year) and males shed significantly higher numbers of eggs.1 A negative binomial model identified young cats as super-shedders, with an incidence rate ratio (IRR) of 8.74 compared to adults (P = .002); males shed at an IRR of 3.67 compared to females (P = .030).
Public health implications and One Health recommendations for urban feline parasite control
The identification of young male cats as super-shedders has practical implications for TNR program design, suggesting age- and sex-targeted deworming could yield outsized reductions in environmental egg burden relative to population-wide treatment. The study authors recommend integrating environmental decontamination, targeted parasite control, and public education into TNR programs as a One Health priority.1
For ID clinicians and public health practitioners, the data strengthen the evidence base for toxocariasis as a neglected urban parasitic disease with meaningful human disease burden. The CDC estimates toxocariasis is among the most common parasitic infections in the United States, with seroprevalence studies suggesting millions of Americans have been exposed. Children playing in soil-contaminated urban environments and immunocompromised patients face the highest clinical risk.
The T. gondii seropositivity finding (8.9%), while lower-prevalence, is also clinically relevant given the risk of severe disease in pregnant women and immunocompromised patients, including those with HIV, who may be exposed to contaminated soil in urban green spaces.
References
Nguyen V, Gurtowski E, Chen J. Zoonotic endoparasites and Toxoplasma gondii seropositivity in free-roaming cats (Felis catus) from New York City boroughs. PLOS One. 2026. doi:10.1371/journal.pone.0351437
CDC. Toxocariasis (Toxocara infection). Centers for Disease Control and Prevention. Accessed July 2026. https://www.cdc.gov/parasites/toxocariasis/index.html
