Morphologic and Molecular Identification of Human Ocular Infection Caused by Pelecitus Nematodes, Thailand

Abstract

Nematodes of the Onchocercidae family, such as Pelecitus spp., are filarial parasites of medical and veterinary importance. Although infections are widely distributed among avian species, only 2 cases of human Pelecitus ocular infection, both in South America, have been reported. We describe a 61-year-old man in northeast Thailand diagnosed with an ocular infection. Morphologic characteristics suggested the causative agent was a female Pelecitus nematode: coiled body, rounded anterior and posterior extremities, a distinct preesophageal cuticular ring, lateral alae, a postdeirid, and a protuberant vulva. Sequences of the 12S rDNA gene indicated 95%-96% identity and cox1 gene 92%-96% identity with published P. copsychi sequences. P-distance for cox1 sequences between the causative agent and P. copsychi was 6.71%. Phylogenetic trees of 12S rDNA and cox1 genes indicated the species differed from but is closely associated with P. copsychi. Healthcare providers should be aware of the threat of ocular infection from Pelecitus spp. nematodes.

Keywords: Pelecitus; Thailand; arboviruses; filariae; helminths; nematodes; ocular parasitosis; parasites; postdeirid; preesophageal cuticular ring; zoonoses.

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 (arrowhead). B) Gonioscopic view revealing a parasite in the inferior anterior chamber angle, lodged in the iris fibers. Precise magnification levels are not available.

Figure 2

Light micrographs of Pelecitus sp. 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. Head (arrow) and tail (arrowhead) are indicated. Scale bar = 250 μm. B) Rounded anterior extremity with preesophageal cuticular ring (arrows). Scale bar = 10 μm. C) Postdeirid (arrowhead) at the posterior left side and lateral alae (arrows) at the posterior part. Scale bar = 50 μm. D) Rounded posterior extremity (arrowhead). Scale bar = 100 μm.

Figure 3

Maximum-likelihood reconstruction of phylogeny on the basis of 12S rDNA sequences of a Pelecitus sp. nematode isolated from the left eye of a 61-year-old man in Thailand (bold text) and reference sequences from GenBank. Bootstrap scores (percentages of 1,000 replications) are presented for each node. GenBank accession numbers are shown. Scale bar refers to a phylogenetic distance of 0.05 nucleotide substitutions per site.

Figure 4

Maximum-likelihood reconstruction of phylogeny on the basis of cox1 sequences of Pelecitus sp. nematode isolated from the left eye of a 61-year-old man in Thailand (bold text) and reference sequences from GenBank. Bootstrap scores (percentages of 1,000 replications) are presented for each node. GenBank accession numbers are shown. Scale bar refers to a phylogenetic distance of 0.05 nucleotide substitutions per site.