Pathogens · 5 authors, 1 centre
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This study found that 3.17% of domestic dogs in Beijing were infected with the zoonotic eyeworm Thelazia callipaeda. Key risk factors included living in mountainous areas, having a history of country park travel, and not receiving anthelmintic treatment, especially during summer and autumn. These findings highlight the importance of regular deworming and avoiding high-risk areas to protect both canine and human health.
**Background:** Thelazia callipaeda is a zoonotic parasitic nematode that infects the ocular conjunctival sac of domestic and wild carnivores, causing thelaziosis. It is transmitted by Phortica spp. fruit flies. While human cases have been reported in China since 1917, the epidemiology in domestic dogs in Beijing was not well characterized. This study aimed to investigate the prevalence and risk factors for ocular thelaziosis in domestic dogs in Beijing.
**Methods:** Between 2018 and 2019, 3215 domestic dogs presented to the China Agricultural University Teaching Animal Hospital in Beijing for ocular health examination. Infection was diagnosed using slit-lamp examination under local anesthesia. Nematodes were collected and identified morphologically and by molecular analysis (PCR and sequencing of the mitochondrial cox1 gene). Clinical data including region, season, age, sex, breed, size, living environment, diet, country park travel history, immunization history, anthelmintic treatment history, and ocular clinical symptoms were recorded. Chi-square tests and logistic regression were used to identify risk factors.
**Key Results:** A total of 102 dogs were infected with T. callipaeda, yielding an overall prevalence of 3.17% (95% CI 2.57–3.78%). The average number of worms per infected eye was 7.80 ± 8.51 (left) and 8.00 ± 9.08 (right). Significant risk factors included: region (mountainous area 4.35% vs. plain area 2.61%, p=0.009), season (summer 4.27% and autumn 4.23% vs. spring 1.92% and winter 1.79%, p=0.002), country park travel history (yes 5.18% vs. no 2.96%, p=0.034), and anthelmintic treatment history (no 4.27% vs. yes 2.62%, p=0.012). Age, sex, breed, size, living environment, diet, and immunization history were not significant. Multivariate logistic regression for summer and autumn showed that dogs living in mountainous areas (OR=4.164, 95% CI 1.023–19.437, p=0.023), with country park travel history (OR=2.382, 95% CI 1.039–28.831, p=0.015), and without anthelmintic treatment (OR=1.438, 95% CI 1.009–2.243, p=0.022) had higher odds of infection. Ocular clinical symptoms were not directly correlated with worm burden; moderate symptoms (increased secretion with conjunctivitis) were most common.
**Clinical Implications:** This study demonstrates that ocular thelaziosis is present in domestic dogs in Beijing, with a prevalence of 3.17%. The significant risk factors—mountainous residence, country park travel, lack of deworming, and summer/autumn season—provide actionable targets for prevention. Regular anthelmintic treatment, especially during high-risk seasons, and avoiding exposure to mountainous or park areas can reduce infection risk. Because T. callipaeda is zoonotic, these measures also protect human health. The finding that asymptomatic infections occur underscores the need for routine ocular screening in at-risk dogs.