Ocular Toxocariasis

Toxocariasis is a zoonotic infection of global importance. Transmission is typically fecal-oral and results from accidental exposure to food, water, or soil contaminated by either dog or, less commonly, cat roundworms – the helminths Toxocara canis and Toxocara cati, respectively. Infection is common and affects approximately 20% of the world’s population, with seroprevalence rates surpassing 80% in some tropical and subtropical regions in Africa and Asia. While many Toxocara infections are asymptomatic, moderate to severe systemic, neurologic, and/or ocular infections can occur. These are referred to respectively as visceral (VLM), neurologic (NVM), and ocular larva migrans (OLM; also known as ocular toxocariasis OT). Three classic patterns or OT have been described, including posterior granuloma – typically submacular or peripapillary and with pronounced retinal striae or folds; peripheral granuloma, often with a vitreoretinal traction band extending toward the posterior pole; and severe, unilateral intermediate or panuveitis referred to as nematode or Toxocara endophthalmitis. Atypical presentations of OT also exist. One metanalysis, three original articles, and one letter in this issue of Ocular Immunology & Inflammation (OII) address aspects of the prevalence, presentation, treatment and outcome of OT. Badri et al. performed a meta-analysis of five English language database listings (PubMed, Scopus, Science Direct, Web of Science, and Google Scholar) from January 1966 to December 2019 to explore the prevalence of OT in six recognized World Health Organization (WHO)-epidemiological regions. A total of 101 studies with 331,602 cases from 35 countries met the inclusion criteria. Overall, studies that utilized immunologic methods, such as serology for nematodespecific antibodies, showed a higher pooled prevalence than those where the diagnosis was based on ophthalmological examination (9%, 95% CI 6–12% vs 1%, 95% CI 1–2%), male subjects were identified slightly more often than female subjects (OR 1.44, 95% CI 0.94–2.20, nominal p < .01), and the diagnosis of OT was made most often in the second decade of life (7%, 95% CI 1–18%, nominal p < .01) vs roughly half that prevalence for other age groups, and regions of lower-middle class income (6%, 95% CI 2–12%, nominal p < .01). The pooled prevalence of OT in the African WHO-epidemiological region was highest at 10% (95% CI 7–13%), followed by the European region at 8% (95% CI 4–12%), the region of the Americas at 6% (95% CI 2–10%), the Eastern Mediterranean and Western Pacific regions at 3% each (95% CI 0–10% and 1–5%, respectively), and the South-East Asia Region at 1% (95% CI 0–3%). It should be noted, however, that only one study was available from Africa – specifically Sierra Leone (10%, 95% CI 7–13%). Other countries of high prevalence included Peru (39%, 95% CI0-99%) and Slovenia (39%, 95% CI17-36%). Pooled prevalences of near zero were identified in Ireland, Germany, Spain and Nepal, and slightly higher at about 1% in Turkey, Myanmar, and the Czech Republic. Identified risk factors for a higher pooled prevalence of OT included ownership of dogs or cats (18%, 95% CI 0–96%), contact with dogs (17%, 95% CI3-39%), consumption of raw or undercooked meat (12%, 95% CI 0–53%), and exposure to soil (6%, 95% CI 0–27%). The anatomic location of inflammation was described most often as intermediate (6%, 95% CI 1–15%), followed by anterior (3%, 95% CI 0–10%), posterior (2%, 95% CI 1–4%), and panuveitis (1%, 95% CI 0–1%). Granulomas, when described, were most often central (5%, 95% CI 3–7%), followed by peripheral (4%, 95% CI1-8%). The authors concluded that their findings were generally in agreement with those of global epidemiologic studies based on the analyses of anti-Toxocara seroprevalence. They also emphasized the importance of considering OT in endemic areas, and of good hygiene, limiting pet exposure to public places, such as playgrounds and parks, and of monitoring and treating dogs and cats for helminthic infections. Martinez et al retrospectively reviewed the epidemiologic and clinical characteristics, as well as treatment and outcome of 157 patients less than 13 years of age with OT seen in a tertiary referral center in Costa Rica between January 1998 and December 2018. All patients had unilateral disease, the mean age was 6.7 ± 2.8 years, 97 (61.8%) were male, 145 (92.4%) had positive serology for T. canis, and 79 (50.3%) had eosinophilia. The most common reasons for consultation included decreased vision (29.9%), strabismus (26.7%), leukocoria (19.7%) and red eye (17.8%). The vast majority of patients presented with vision between 20/200 and no light perception (NLP, 89.2%). Associated ocular complications included cataract (17.5%), posterior synechiae formation (9.7%), band keratopathy (3.9%), and hypopyon formation (1.3%). The posterior segment could not be visualized in 12.7% of affected eyes. In the remaining eyes, a peripheral granuloma was identified in 57 (54.2%), a posterior granuloma in 27 (25.8%), and no granuloma in 21 (20.0%). Eighty-eight (56.1%) had a retinal detachment (RD). Treatments were tailored to findings and included no therapy in 64 eyes (40.8%), use of prednisone in 32 eyes (20.4%), pars plana vitrectomy (PPV) alone in 23 eyes (14.6%), prednisone plus thiabendazole in 16 eyes (10.2%), cataract surgery in 9 eyes (5.7%), 5 eyes (3.2%) treated with thiabendazole alone, and 3 eyes (1.9%) treated with regional corticosteroids alone. Most eyes with RD failed to show functional improvement despite treatment. The authors concluded that OT is an important cause of moderate-to-severe vision loss in Costa Rica, and that RD, in particular, is a predictor of poor visual outcome. Wang and Tao retrospectively reviewed the clinical characteristics, pattern of inflammatory cytokines, ocular complications and predictors of recurrence of inflammation within 6 months of presentation and treatment in a cohort OCULAR IMMUNOLOGY AND INFLAMMATION 2021, VOL. 29, NOS. 7–8, 1243–1245 https://doi.org/10.1080/09273948.2021. 2018825