Novel Etiological Agent: Molecular Evidence for Trematode-Induced Anterior Uveitis in Children

Histopathological analysis has provided support that trematode infections can cause a characteristic granulomatous anterior uveitis in children from South India.¹ Southeast Asian populations are exposed to at least 70 species of foodborne and waterborne trematodes. The burden of disease and current distribution of the parasites within the population are largely unknown, however.² Serologic testing is unreliable mainly because of cross-reactive antigens.² Fecal egg identification likewise has limited utility because humans act as accidental hosts. Molecular diagnostic studies, in contrast, can identify individual species of trematodes involved in site-specific infections. In this study, we have applied polymerase chain reaction–based techniques to identify the trematode Procerovum varium as a cause of granulomatous anterior uveitis in children from South India.

A 9-year-old boy from the village of Jagathapatinum in Tamil Nadu, India, came to the hospital with a 2-week history of left eye redness, which he said started after bathing in the village pond. There was no history of trauma. Visual acuity was 20/20 OU and intraocular pressures were normal bilaterally. Slitlamp examination of the left eye revealed a normal conjunctiva and cornea. A whitish granuloma was seen in the anterior chamber at the 6-o’clock position (Figure 1A). Fundus examination findings were normal. Systemic examination revealed a normal complete blood cell count and no evidence of tuberculosis, syphilis, or sarcoidosis. Stool and urine examination findings were unremarkable. Following informed consent, both aqueous fluid and the granuloma were aspirated using a 25-gauge needle under general anesthesia. The aqueous fluid was sent for cellular analysis, which revealed a predominance of eosinophils, consistent with our previously published work¹ (Figure 1B). Extraction of DNA from the granuloma was performed using a Qiagen polymerase chain reaction purification kit. Snails from the same village pond were collected for cercarial isolation in our laboratory (Figure 1C and D). The snails that released the cercarial larvae were sent to the Zoological Survey of India, Calcutta, India, where they were identified as Melanoides tuberculata. Real-time polymerase chain reaction was performed using the SYBR-Green assay on both the granuloma and cercarial DNA. A standard protocol³ was followed, using the universal forward primer AP101 (5′-AGAGCGCAGCCAACTGTGTGA-3′) and reverse primer AP101 (5′-TGCCACGTCCTAGCATCAGCC-3′). Nuclease-free water was used as a negative control and Fasciola gigantica DNA was the positive control⁴ (Figure 2). The amplified DNA was loaded on a 2% agarose gel and found to be a 369–base pair fragment of the ribosomal DNA spanning the internal transcribed spacer 2 region. Bidirectional sequencing and Basic Local Alignment Search Tool analysis were carried out using a standard protocol.³ Both the environmental cercaria and the granuloma revealed maximal similarity with P varium —a trematode of the family Heterophyidae (Figure 2D).

Granulomatous uveitis has traditionally raised concern for tuberculosis infection among patients seen in regional hospitals of South India. Many South Indian children with granulomatous anterior uveitis have received antituberculosis treatment, which has proven ineffective.^1,5 Notably, these patients typically describe a strong temporal association between the onset of symptoms and having bathed in regional ponds or waterways. Recently, our histopathological study of affected ocular tissues suggested the presence of a trematode infection,¹ which we have now identified as P varium. Snails act as the first intermediate host for this trematode in regional ponds, where they release cercarial larvae to infect the fish, which act as second intermediate hosts. Infected fish then transmit the trematode to birds.⁶ Fish-eating birds are the definitive hosts, while infected children become accidental hosts. Our data, together with the clustering of cases of granulomatous anterior uveitis in children from South Indian villages, suggest that trematode infection may be common in areas where fish and waterfowl infection is endemic.

Correspondence: Dr Rathinam, Uveitis Service, Aravind Eye Hospital and P. G. Institute of Ophthalmology, 1, Anna Nagar, Madurai, Tamil Nadu 625 020, India (rathinam@aravind.org).

Author Contributions: All the authors had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Funding/Support: This work was supported by the Aravind Medical Research Foundation.

Additional Contributions: Shanthi Rathakrishnan, MD, read the hematoxylin-eosin–stained slide of aqueous fluid.