Morphological and Molecular Identification of Oestrus ovis (Diptera: Oestridae) Larvae Collected from a Chinese Patient with Conjunctival Myiasis.

Abstract

Human conjunctival myiasis, which is often misdiagnosed or missed clinically, is commonly caused by Oestrus ovis larvae. Here, pathogenic identification was performed for two maggots collected from a patient from China, to provide a clinical scientific basis for diagnosis and treatment. Morphological identification was performed using a microscope. Oestrus mtDNA cox1 and rDNA 28S were selected as target genes for duplex PCR amplification, followed by cloning, sequencing, and identification. Morphological examination showed that the maggots were approximately 1.0-1.5mm long, long-oval-shaped, segmented, and covered with small spines, with a pair of hooks in the scolex and claw-like spines at the telson. Therefore, they were identified as the first-instar larvae of O. ovis. Duplex PCR detected products of approximately 400 and 200bp, consistent with the size of designed cox1 and 28S D7a gene fragments, respectively. Sequences of cox1 and 28S D7a from the samples in question had 99.5-100.0% and 96.2-100.0% similarity (respectively) to GenBank sequences of O. ovis specimens known to parasitize sheep, goats, and humans. However, some 28S D7a sequences exhibited 89.7-90.6% similarity to GenBank sequences of Oestrus sp. known to parasitize Capra pyrenaica (Artiodactyla: Bovidae) (Iberian ibex). Therefore, we considered that the larvae infecting the patient originated from sheep or goats, not Iberian ibex. The phylogenetic trees supported this conclusion. This study implemented the first duplex PCR molecular identification of O. ovis larvae parasitizing human eyes in China as a complementary approach to morphological identification. Our results indicate that molecular tools can be utilized to aid in the diagnosis of opthalmomyiasis.