Ocular Gnathostomiasis Mimicking Ocular Toxocariasis: An Atypical Manifestation of a Neglected Tropical Disease

Background Gnathostomiasis is a neglected food-borne zoonotic disease endemic in Southeast Asia and other tropical regions. Ocular involvement is rare and typically presents with anterior segment inflammation or visible intraocular larvae. Posterior segment manifestations are uncommon and may pose substantial diagnostic challenges, particularly in endemic settings where multiple parasitic infections coexist. Case presentation: A 12-year-old boy from Thailand presented with a six-month history of progressive unilateral visual loss. Ophthalmic examination revealed chronic posterior uveitis with dense vitreous inflammation, a peripheral retinal granuloma, and tractional retinal detachment. There was no anterior segment inflammation, no visible intraocular parasite, and no peripheral eosinophilia. Based on the clinical features and exposure history, ocular toxocariasis was initially suspected, and empiric antiparasitic therapy was initiated. Due to significant retinal traction, pars plana vitrectomy with membrane peeling and silicone oil tamponade was performed. Histopathological and cytological analyses of intraocular specimens demonstrated inflammatory reactions without identifiable parasitic structures. Subsequent serologic testing showed positive Gnathostoma -specific antibodies, while tests for Toxocara and other parasitic infections were negative, leading to a revised diagnosis of ocular gnathostomiasis. The patient received prolonged albendazole therapy and corticosteroids. Ocular inflammation gradually resolved, and retinal attachment was maintained, although visual recovery remained limited. Conclusions This case illustrates an atypical presentation of ocular gnathostomiasis mimicking ocular toxocariasis, characterized by posterior uveitis with retinal granuloma and tractional retinal detachment in the absence of classical systemic or ocular findings. In endemic areas, gnathostomiasis should be included in the differential diagnosis of unilateral posterior uveitis. Early recognition and appropriate diagnostic evaluation are important to reduce vision-threatening complications associated with neglected tropical diseases.