Morphological and Mitochondrial Genomic Characterization of Eyeworms (Thelazia callipaeda) from Clinical Cases in Central China

Abstract

Thelazia callipaeda, also called the oriental eyeworm, is the major etiological agent of human thelaziasis. Cases of thelaziasis have increased in recent years in China. Although this species is of medical importance, the genetics and phylogenetic systematics of T. callipaeda are poorly understood. In this study, we first reported three cases of thelaziasis in central China. All clinical isolates were identified as T. callipaeda according to morphological characteristics by light microscopy and scanning electron microscopy. Next, complete mitochondrial (mt) genomes for the three T. callipaeda isolates from different geographical locations were fully characterized using an Illumina sequencing platform. In addition, all available mt genomes of spirurid nematodes in GenBank were included to reconstruct the phylogeny and to explore the evolutionary histories of the isolates. The genome features of the T. callipaeda isolates contained 12 PCGs, 22 transfer RNA genes, two ribosomal RNA genes and a major non-coding region. The mtDNA nucleotide sequences of the T. callipaeda isolates from different hosts and different locations were similar. The nad6 gene showed high sequence variability among all isolates, which is worth considering for future population genetic studies of T. callipaeda. Phylogenetic analyses based on maximum parsimony and Bayesian inference methods revealed close relationships among Thelaziidae, Onchocercidae, Setariidae, Gongylonematidae, Physalopteridae, Dracunculidae, and Philometridae. The monophyly of the T. callipaeda isolates from different hosts and distinct geographical locations was confirmed. The entire mt genomes of T. callipaeda presented in this study will serve as a useful dataset for studying the population genetics and phylogenetic relationships of Thelazia species.

Population structure analysis of the neglected parasite Thelazia callipaeda revealed high genetic diversity in Eastern Asia isolates

“…Recently, an increase in T . callipaeda infections has been reported in animals and humans living in European countries and in China [ 6 , 11 ].…”

Ocular thelaziasis: A case report from Assam, India

“…Another genetic marker, the nicotinamide dehydrogenase complex 6 gene has also been shown to have high sequence variability among all isolates, which is worth considering for future population genetic studies of T. callipaeda . [20]…”

The Third Man: DNA sensing as espionage in pulmonary vascular health and disease

“…Finally, application of external radiation (either ambient or therapeutic) acts to increase interferon activity through STING activation 137 , an exposure known to induce acute pneumonitis and chronic lung fibrosis 138 . Interestingly, mtDNA released by tumor cells elicits a STING priming effect in circulating innate immune cells, responsible for the abscopal response of distant tumor burden after treatment 139 . Although the pathology of disease is complex, the latter phenomenon may in part explain downstream protection against direct and indirect radiation-induced pulmonary fibrosis through blocking TBK1 phosphorylation and IRF3 nuclear translocation 140 .…”

“…138 Interestingly, mtDNA released by tumor cells elicits a STING priming effect in circulating innate immune cells, responsible for the abscopal response of distant tumor burden after treatment. 139 Although the pathology of disease is complex, the latter phenomenon may in part explain downstream protection against direct and indirect radiation-induced pulmonary fibrosis through blocking TBK1 phosphorylation and IRF3 nuclear translocation. 140 While broad thoracic radiation has been demonstrated to result in development of PH in sheep, 141 reprogramming of circulating myeloid cells in response to soluble factors of vascular injury may explain why even partial lung irradiation in rats results in out-of-field changes to pulmonary vessels and PH.…”