Case Report

An otherwise healthy 61-year-old man in Thailand sought treatment for gradually increasing eye pain, redness, light sensitivity, and slight vision loss in his left eye. Symptoms persisted for ≈1 month. He was a farmer in northeastern Thailand and had not traveled outside the country. He regularly consumed traditional dishes containing raw and partially cooked ingredients, including beef and fish. He was diagnosed with an intraocular parasite at a private clinic, where staff performed an Nd:YAG (neodymium-doped yttrium aluminum garnet) laser procedure to immobilize the parasite before the patient was referred to the hospital. We postulate that the infection in this patient might have resulted from a bite from a hematophagous arthropod.

Figure 1

Figure 1. Slit-lamp examination of the left eye of a 61-year-old man in Thailand with ocular parasitosis. A) Ciliary injection and a live parasite in the inferior part of the anterior chamber...

Upon examination, the patient had best-corrected visual acuity of 20/20 in the right eye and 20/40 in the left eye. Intraocular pressure measurements were 18 mm Hg in the right eye and 14 mm Hg in the left. The right eye examination was unremarkable, but the left eye showed ciliary injection (Figure 1, panel A) and grade 1+ anterior chamber cells. A live, moving parasite was observed in the inferior anterior chamber, more distinctly during gonioscopic examination (Figure 1, panel B). The posterior segment was within reference limits. Complete blood count results showed leukocytosis of 12,640 cells/mm³ and eosinophilia of 5.5% (absolute eosinophil count 695.2 cells/mm³). Fecal examination did not reveal parasites or eggs.

We performed urgent surgical removal to prevent posterior or extraocular migration. After the operation, we treated the patient with prednisolone acetate 1% eye drops (every 2 h), moxifloxacin 0.5% eye drops (4×/d), and oral albendazole (400 mg 2×/d for 5 d). At 1-month follow-up, the patient returned with a reduction in pain and redness. The best-corrected visual acuity was 20/30 and the intraocular pressure 10 mm Hg in the left eye. We found no active inflammation upon slit-lamp examination. Prednisolone acetate 1% eye drops were gradually tapered. At the 1-year follow-up, the patient was doing well without recurrence of ocular symptoms. We did not perform a blood test at follow-up.

Morphologic Identification of the Parasite

We fixed the causative agent in 70% ethanol and subsequently cleared it in lactophenol (R & M Chemicals, https://www.evergreensel.com.my) for morphologic examination under a compound microscope equipped with an Olympus U-DA camera lucida (https://www.olympus-global.com). We extracted DNA from the caudal part of the causative agent (0.2 mm) using the Nucleospin Tissue kit (Macherey-Nagel, https://www.mn-net.com) according to manufacturer instructions. We performed a conventional PCR to amplify the targeted mitochondrial 12S rRNA and cox1 genes, according to instructions for specific primers and PCR conditions described elsewhere (13–15). Afterward, we sequenced the PCR products using the Applied Biosystems DNA Analyzer (ThermoFisher, https://www.thermofisher.com). We compared the 12S rDNA and cox1 sequences with public sequences in the GenBank database by using BLASTn (https://blast.ncbi.nlm.nih.gov).

We performed multiple sequence alignment of DNA sequences from the 12S rRNA and cox1 genes with ClustalW (http://www.clustal.org) using MEGA-X (https://www.megasoftware.net). We constructed phylogenetic trees using the maximum-likelihood method with 1,000 bootstrap resamplings as implemented in MEGA-X (16). We used publicly available sequences from different nematode species for comparison. We selected the Hasegawa–Kishino–Yano model as a suitable substitution model (17).

Morphologic Identification

Figure 2

Figure 2. Light micrographs of Pelecitussp. nematode isolated from the left eye of a 61-year-old man in Thailand. A) Curled female, 3.5 mm in length and 198 µm in width....

The surgically removed female nematode had a coiled body, 3.5 mm long and 198 μm wide at the midbody (Figure 2, panel A). The head was bluntly rounded and the preesophageal cuticular ring (6.3 µm wide × 2.5 µm high) was distinct (Figure 2, panel B). Labial and cephalic papillae, arranged in 4 submedian pairs, were not markedly protuberant. Amphids were small, lateral, and not salient. A slight neck was found 69 µm from the anterior extremity. The nerve ring was situated 138 µm from the anterior extremity. The esophagus was 608 µm long, and its diameter slightly widened in the posterior half. The vulva was located at the level of the posterior half of the esophagus, 395 µm from the anterior extremity. No microfilariae were present in the uteri. A postdeirid was found on the left side, 300 µm from the caudal extremity (Figure 2, panel C). Lateral alae were present, broadening toward the posterior extremity. At the level of the postdeirid, the ala was 28 µm wide. The intestine was filled with brown pigments. The cuticle was thick, 5–10 µm wide, at the postdeirid level. The tail extremity was rounded (Figure 2, panel D). We deposited the specimen (MNHN-114YT) in the Muséum National d’Histoire Naturelle, Paris, France (https://www.mnhn.fr).

Molecular Analyses

Figure 3

Figure 3. Maximum-likelihood reconstruction of phylogeny on the basis of 12S rDNA sequences of a Pelecitussp. nematode isolated from the left eye of a 61-year-old man in Thailand (bold text)...

Figure 4

Figure 4. Maximum-likelihood reconstruction of phylogeny on the basis of cox1 sequences of Pelecitussp. nematode isolated from the left eye of a 61-year-old man in Thailand (bold text)...

Based on the best match in BLAST, the 12S rDNA sequence (468 bp) (Figure 3) showed 95%–96% identity with P. copsychi (GenBank accession nos. OK480976 and OK480977) and the cox1 sequence (611 bp) (Figure 4) showed 92%–96% identity with P. copsychi (GenBank accession nos. OK480041 and OK480043). The calculated p-distance for cox1 sequences between this causative agent and P. copsychi was 6.71%. We submitted sequences generated in this study to GenBank (accession nos. OR346706 [cox1] and OR396900 [12S rRNA]).