Toxocariasis presenting with peripheral eosinophilia and eosinophilic pleural effusion: A case report.

Human toxocariasis is a parasitic infection caused by Toxocara species and is important in the differential diagnosis of patients presenting with unexplained eosinophilia. A case of toxocariasis with an eosinophilic pleural effusion is presented. A 67-year-old Japanese man presented with progressive dyspnea. Laboratory investigations showed marked peripheral eosinophilia and a markedly elevated serum immunoglobulin E level. Chest imaging demonstrated bilateral ground-glass opacities and a left-sided pleural effusion. Analysis of the pleural fluid showed eosinophil predominance without evidence of malignancy or bacterial infection. Extensive diagnostic evaluations, including autoimmune serology, bone marrow examination, and genetic analyses for myeloid neoplasms with eosinophilia, yielded negative results. Serological test using an enzyme-linked immunosorbent assay demonstrated elevated anti-Toxocara antibody level, which were subsequently confirmed by Western blot analysis, leading to a diagnosis of human toxocariasis presenting with visceral larva migrans. The patient had no clear history of animal contact or ingestion of raw meat or liver. Treatment with oral albendazole for four weeks resulted in marked clinical improvement, with resolution of the pleural effusion and pulmonary infiltrates, normalization of peripheral eosinophil counts, and a significant decrease in anti-Toxocara antibody level. This case emphasizes the importance of considering toxocariasis in the differential diagnosis of an eosinophilic pleural effusion and pulmonary infiltrates, even in the absence of identifiable exposure risks. Early serological testing can facilitate prompt diagnosis and appropriate anthelmintic therapy, potentially preventing unnecessary invasive procedures and delayed treatment.