Abstract
Human thelaziosis is an underestimated parasitic disease caused by Thelazia species (Spirurida: Thelaziidae). The oriental eyeworm, Thelazia callipaeda, infects a range of mammalian definitive hosts, including canids, felids and humans. Although this zoonotic parasite is of socio-economic significance in Asian countries, its genetics, epidemiology and biology are poorly understood. Mitochondrial (mt) DNA is known to provide useful genetic markers to underpin fundamental investigations, but no mt genome had been characterized for any members of the family Thelaziidae. In the present study, we sequenced and characterized the mt genome of T. callipaeda. This AT-rich (74.6%) mt genome (13,668 bp) is circular and contains 12 protein-coding genes, 22 transfer RNA genes and two ribosomal RNA genes, but lacks an atp8 gene. All protein-coding genes are transcribed in the same direction; the gene order is the same as those of Dirofilaria immitis and Setaria digitata (Onchocercidae), but distinct from Dracunculus medinensis (Dracunculidae) and Heliconema longissimum (Physalopteridae). Phylogenetic analyses of the concatenated amino acid sequence data for all 12 protein-coding genes by Bayesian inference (BI) showed that T. callipaeda (Thelaziidae) is related to the family Onchocercidae. This is the first mt genome of any member of the family Thelaziidae and should represent a new source of genetic markers for studying the epidemiology, ecology, population genetics and systematics of this parasite of humans and other mammals.
Highlights
Thelazia callipaeda Railliet and Henry, 1910, known as the ‘oriental eye-worm’, because of its geographical distribution in Asian countries, is frequently reported as being responsible for thelaziosis of humans, carnivores and rabbits, causing mild to severe clinical signs [1]
Scant attention has been paid to human thelaziosis, and there are difficulties in its clinical diagnosis and differentiation from allergic conjunctivitis, when small numbers of adult or larval stages of T. callipaeda are present in the eyes of infected patients
Human thelaziosis is an underestimated parasitic disease caused by the eyeworm Thelazia callipaeda (Spirurida: Thelaziidae)
Summary
Thelazia callipaeda Railliet and Henry, 1910, known as the ‘oriental eye-worm’, because of its geographical distribution in Asian countries (including China, India, Japan, Korea and Thailand), is frequently reported as being responsible for thelaziosis of humans, carnivores (dogs, foxes and cats) and rabbits, causing mild to severe clinical signs (including lacrimation, epiphora, conjunctivitis, keratitis and/or sometimes corneal ulcers) [1]. After being ingested by the fly, the T. callipaeda larvae migrate in the vector’s body (i.e. testis of the male) and undergo development from the L1 to the infective, third-stage larvae (L3) within 14–21 days. Following this migration, the L3s of Thelazia emerge from the labella of the infected fly, are deposited on the eye, as the vector feeds on lacrimal secretions, and develop into the dioecious adult stages in the ocular cavity within ,35 days [5]
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