Emerging trends in parasitic uveitis due to Gnathostoma spinigerum: A case series and diagnostic challenge

Dear Editor, Gnathostoma spinigerum-induced parasitic uveitis is an uncommon condition frequently exhibiting unusual clinical characteristics. Gnathostoma spinigerum is a nematode primarily found in Southeast Asia, with humans serving as incidental hosts through consumption of undercooked freshwater fish or poultry.[1,2] Previously, Gnathostoma-induced uveitis was sporadic. Once viewed as a singular event, the occurrence seems to be on the rise. We present a case series from a tertiary eye care facility in South India, detailing four instances in 2024, as opposed to just one case each in 2010 and 2022. This report presents each with distinct presentations, identified through slit-lamp examination followed by histomorphological confirmation. A 54-year-old man presented with pain, redness, headache, dizziness, and impaired vision in the right eye, following travel from Myanmar. He reported gastrointestinal symptoms a week prior to consuming fish, for which he was treated for presumed gastroenteritis. Ophthalmic examination showed retinal scarring and bleeding, leading to a provisional diagnosis of quickly advancing retinitis with vasculitis. Persistent symptoms led to repeat slit-lamp examination, revealing a live motile worm in the anterior chamber, which was removed by anterior chamber tapping. A 40-year-old woman presented with sudden visual loss and sensitivity to light. A month prior, she had experienced persistent headaches following a meal, after which a brain MRI revealed mild widespread cerebral edema, and treated for bacterial meningitis. Ophthalmic examination revealed a motile worm in the vitreous cavity. Based on the clinical findings and neurological history, a diagnosis of parasitic uveitis, likely secondary to systemic infestation, was considered. Worm extraction was done via pars plana vitrectomy (PPV), along with internal limiting membrane (ILMP) and epiretinal membrane (ERMP) peeling. A 28-year-old man without any previous eye issues presented with worsening blurred vision, headaches, and floaters. Clinical observations indicated granulomatous uveitis. Differential diagnosis was considered occlusive vasculitis due to a presentation similar to inferior hemi-retinal vein occlusion (HRVO). Upon a follow-up after three days, the symptoms remained unchanged. Slit-lamp examination revealed a motile worm surfaced in the inferior angle projecting into the anterior chamber behind the corneal endothelium. A live worm was removed with anterior chamber tapping without pupillary dilatation to avoid posterior migration. A 47-year-old male fisherman with no prior ocular history presented with sudden-onset blurred vision, headaches, and floaters. He also reported a history of migratory subcutaneous swellings. Initially misdiagnosed as ocular cysticercosis at another facility, he was referred for further evaluation. Fundus examination revealed the presence of a worm in the media along with disc swelling. Through PPV, fluid-air exchange (FAE) followed by endo laser (EL) treatment with worm removal was done. In all our instances, with persistent symptoms after initial management for inflammatory or autoimmune etiology, repeat slit-lamp examination revealed a motile worm in the anterior chamber or vitreous. Anterior chamber tapping and worm removal were conducted without the use of pharmacologic dilation to avoid posterior migration of worms. Surgically extracted parasites of all the reported cases were submitted for histomorphological confirmation [Fig. 1]. Through the detailed microscopic examination of the morphological features alone, the species-level identification was established as Gnathostoma spinigerum in all our cases [Figs. 1 and 2]. Molecular analysis was done in none of our cases. Patient’s ocular inflammation resolved completely with adjunct anti-inflammatory therapy. Based on these clinical scenarios of unilateral uveitis, a systematic approach is formulated as a diagnostic flowchart [Fig. 3].Figure 1: (a) Slit-lamp examination – Single Gnathostoma spinigerum larva observed floating in the anterior chamber. b, c and d: Light microscopy: (b) The intact larva has a cylindrical, elongated body with a slightly tapered posterior end. (c) Distinctive cephalic bulb armed with four rows of cuticular spines and segmented body with transverse rows of spines. (d) Internal organs, including digestive structures (a: Esophagus and b: Intestine), ending with anus c: at the posterior end of the tail, are visible. (e) Gross image: Advanced 3rd stage larval form of nematode Gnathostoma spinigerum with a translucent white cylindrical body. (f) Histopathology image (hematoxylin and eosin staining, longitudinal section): The larva displays a multi-layered cuticle with spines, underlying muscle layers, and internal structures such as the digestive tract (a: Esophagus, b: Cuticle, c: Muscle layers)Figure 2: (a) Gross image of G. spinigerum. (b-d) Light microscopic images of other casesFigure 3: Unilateral uveitis – a diagnostic approachDiscussion This case report underscores the rising and frequently neglected eye complications associated with Gnathostoma spinigerum infections, highlighting the difficulties in diagnosis, with diverse clinical symptoms. Gnathostoma spinigerum uveitis closely resembles autoimmune and infectious uveitic syndromes, frequently resulting in a delayed diagnosis.[3] Imaging and lab tests frequently lack specificity.[4] In all the cases, visualization of the motile worm using slit-lamp biomicroscopy or intraoperative microscopy and subsequent histomorphological confirmation remains the diagnostic gold standard. Surgical removal continues to be the primary method of treatment.[5] Confirming the species clarifies that the infection is caused by migrating larvae. As there is no active reproduction or risk of auto-infection, the treatment aims to eliminate the larvae and manage inflammation rather than disrupt a reproductive cycle. As a result of diagnostic rapidity, postoperative care concentrated on managing inflammation while avoiding extended immunosuppression. This case report highlights the significance of maintaining clinical awareness and conducting repeated and comprehensive slit-lamp examinations in unusual or refractory uveitis cases, which eventually identified the parasite. Conclusion Parasitic uveitis due to Gnathostoma spinigerum is an emerging concern requiring increased clinical suspicion, particularly in endemic areas. Prompt diagnosis through slit-lamp examination and early surgical intervention are critical to preserving vision. The recent rising trend compared to sporadic incidents in earlier years reflects the potential epidemiological change correlating with the history of frequent travel to endemic areas and consumption of undercooked fish. It emphasizes the importance of raising public health awareness, especially in areas where the disease is commonly found. Healthcare providers should include ocular gnathostomiasis in their differential diagnosis when dealing with unexplained uveitis. Further epidemiological studies are needed to assess risk factors and formulate preventive strategies. Abbreviations PPV – Pars plana vitrectomy. ILMP – Internal limiting membrane peeling. ERMP – Epiretinal membrane peeling. FAE – Fluid-air exchange. EL – Endo laser. HRVO – Hemi-retinal vein occlusion. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship: Nil. Conflicts of interest: There are no conflicts of interest.