Study links toxocariasis exposure and eye findings in people, dogs: full analysis

CURRENT FULL VERSION: Toxocariasis is back in focus through a One Health lens after researchers in southern Brazil paired human serology with canine parasitology and ophthalmic exams in both species, then found a striking mismatch: about one-third of people tested positive for prior exposure, while direct egg detection in dogs was relatively uncommon. The study, published February 24, 2026, in Scientific Reports, examined 342 people and 237 dogs living in a coastal Atlantic Forest region and argues that shared exposure may be easier to miss if clinicians rely too heavily on fecal findings alone. (nature.com)

That framing builds on earlier One Health work from the same research network. A 2021 study in nearby seashore mainland and island communities in southern Brazil reported even higher human seroprevalence, 64.6%, alongside 10.4% positivity in dog feces, 21.2% contamination in dog hair, and widespread environmental contamination in sand samples. The newer paper appears to extend that line of inquiry by adding structured ophthalmic assessment in pet parents and dogs, aiming to capture not just exposure, but possible ocular consequences and household-level signals of risk. (pubmed.ncbi.nlm.nih.gov)

In the new study, 112 of 342 participants, or 32.7%, were seropositive for anti-Toxocara IgG. In univariate analysis, family income was associated with seropositivity, but the final logistic model retained different factors: having dogs and cats, soil contact, and artesian well water as risk factors, while higher education was protective. On the canine side, eggs were seen in 6 of 216 fecal samples and 5 of 236 hair samples. Untreated water increased the odds of canine contamination or infection 6.3-fold, while purebred status and outdoor access were identified as protective factors in the model. (nature.com)

The ophthalmic findings were more exploratory, but they’re what make the paper especially notable for clinicians. Only one human participant had a lesion considered highly suggestive of ocular toxocariasis in a cicatricial stage, and that person was seropositive. Another 32 participants had retinal scars compatible with prior chorioretinitis, though the authors note those lesions were not specific and could reflect other causes, including toxoplasmosis. Among dogs, 205 of 237, or 86.5%, had at least one ophthalmic abnormality, mostly chronic ocular surface and adnexal lesions. Fundus changes were seen in 20 dogs, Florida Spot Keratopathy in 12, and presumed retinopathies were significantly associated with Toxocara positivity. The authors also reported that dogs with suggestive fundoscopic signs of retinopathy were more than eight times as likely to belong to a household with at least one seropositive person, though they were careful to frame this as an epidemiologic correlation, not evidence of ocular transmission from dogs to humans. (nature.com)

That caution matters. CDC notes that humans are accidental hosts infected by ingesting infective eggs or, less commonly, undercooked tissues from paratenic hosts, and that ocular larva migrans can cause permanent visual damage or blindness. Long-standing veterinary public health reviews add useful context here: Toxocara species in dogs and cats are the cause of human toxocarosis, which can present as visceral, ocular, neurological, or covert disease. They also emphasize that eggs shed in fresh feces are not immediately infective; they generally require 2 to 7 weeks in the environment to embryonate to the infective L3 stage. In dogs, the life cycle is complex, and transplacental transmission is considered a major route of infection, helping explain why puppies can have very high infection rates if dams are untreated, while adult pets often show lower patent prevalence because immunity reduces egg shedding. In other words, the Brazilian study’s low dog egg counts shouldn’t be read as reassurance; they may instead reflect the limits of spot sampling in a parasite with intermittent shedding, age-related differences in patent infection, and substantial environmental persistence. (cdc.gov)

For veterinary teams, the practical message is less about diagnosing ocular toxocariasis from routine eye findings and more about using those findings, along with household history, as a prompt for broader prevention conversations. A dog with nonspecific ocular changes is not proof of zoonotic transmission risk, but in endemic or higher-risk settings, it may be one more reason to review deworming history, water source, outdoor exposure, feces disposal, and whether pet parents understand how environmental contamination drives infection. The study also reinforces the value of talking about zoonotic parasite prevention as a family health issue, especially in communities where untreated water, soil exposure, and lower access to preventive care overlap. It also supports a point veterinary public health authors have made for years: prompt feces removal matters because fresh stool is not the main zoonotic hazard, but stool left in the environment long enough to embryonate is. (nature.com)

There are important limitations. This was a cross-sectional study, human serology indicates exposure rather than active disease, ocular lesions were not followed longitudinally, and many canine eye findings were nonspecific. The authors themselves call for more refined diagnostics, including canine serology, ocular ultrasonography, and molecular testing, to clarify whether some retinal findings reflect ocular larva migrans, immune-mediated sequelae, or unrelated disease. (nature.com)

Why it matters: For veterinarians, this is a reminder that toxocariasis control sits at the intersection of preventive medicine, client education, ophthalmology, and public health. The most useful clinical takeaway may be that household exposure can remain substantial even when direct parasite detection in dogs is low, which argues for consistent parasite control protocols, attention to puppies and breeding females because of transplacental risk, and clearer communication with pet parents about environmental risk, not just individual fecal results. (nature.com)

What to watch: The next step is whether follow-up studies can validate canine ocular findings as a meaningful sentinel tool for shared exposure and define which diagnostics are practical enough to move this from an interesting research signal into everyday veterinary use. (nature.com)