Toxocariasis in immigrants and travelers with unexplained eosinophilia

TL;DR

The study finds that Toxocara canis infection is a common but often overlooked cause of unexplained high eosinophil levels in immigrants and travelers from tropical regions.

Contribution

The study highlights the underrecognized role of Toxocara canis in causing eosinophilia and advocates for including Toxocara serology in diagnostic workups.

Findings

23% of tested patients had T. canis antibodies, with most being immigrants from Africa and Latin America.

Eosinophilia under 1000 cells/μL was significantly associated with T. canis seropositivity.

40.9% of T. canis-positive patients were asymptomatic, indicating silent infection.

Abstract

Eosinophilia is common in immigrants and travelers and is often linked to parasitic infections. While well-known helminths are routinely considered, Toxocara spp. remains underrecognized despite its global prevalence. This study aimed to identify undiagnosed T. canis infections in migrant and traveler patients from tropical and subtropical regions with eosinophilia of unknown etiology.

We retrospectively analyzed patients evaluated at the Tropical Medicine Unit of the Complejo Asistencial Universitario de Salamanca between 2008 and 2023. Eligible participants were immigrants or travelers from tropical and subtropical regions with eosinophilia and complete clinical records. Noninfectious causes were excluded before testing. Serum samples from patients without a confirmed parasitic diagnosis were screened for anti-T. canis immunoglobulin (Ig)G antibodies via enzyme-linked immunosorbent assay (ELISA), and positive results were confirmed via western blot. Demographic, clinical, and laboratory data were collected, and univariate analyses were used to assess associations with T. canis seropositivity.

Of the 192 patients tested, 44 (23.0%) were positive by ELISA, and 41 of 192 patients were confirmed by Western blot, the three discordant cases were considered indeterminate. Most were immigrants (37 of 41; 90%) from Africa (21 of 41; 51.2%) and Latin America (20 of 41; 48.8%), with a mean age of 28 years. Absolute eosinophilia was present in 70.5% of the positive patients, with a median eosinophil count of 946.4 cells/μL and a median total IgE level of 473 U/mL. Common symptoms included gastrointestinal complaints (41.7%), pruritus (37.5%), and fever (12.5%), while 40.9% were asymptomatic. Eosinophilia < 1000 cells/μL was significantly associated with seropositivity (OR 3.2, 95% CI 1.3–7.6; P = 0.009).

T. canis infection is an important and frequently underrecognized cause of eosinophilia in immigrants and travelers. The systematic inclusion of Toxocara serology in the workup of unexplained eosinophilia, after ruling out common etiologies, may improve detection and guide management.

The online version contains supplementary material available at 10.1186/s13071-026-07300-9.

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