Morphological and molecular characterization of Setaria equina in donkeys

Abstract

Background: Adult worms of Setaria equina mainly found in the peritoneal cavity of equine. They were nonpathogenic but might induce varied degrees of peritonitis and might migrate to the eye, brain, lung, and scrotum causing lacrimation, blindness, paraplegia, locomotor, and neurological disturbances. Identification by light microscopy is insufficient to differentiate Setaria species, and so scanning electron microscopy (SEM) is required to observe their ultrastructures. The study was performed on 80 donkeys from May 2018 to January 2019 for the detection of microfilaria in blood and the adult worms in the peritoneal cavity. The blood samples were either stained with Giemsa stain or examined by modified Knott’s technique for the detection of microfilariae. Adult worms were morphologically characterized based on light microscope and scanning electron microscopy (SEM). PCR was performed targeting the 12S rRNA gene followed by sequencing and phylogenetic analysis. Results: The current study recorded 21.6% and 16.2% prevalence rates for adult worms and microfilariae, respectively. By using SEM, this study was able to clarify the detailed structure of amphids, predeirids, vulva, arrangement, and number of male caudal papillae. PCR amplified products for 12S rRNA gene (408 bp) for adult worm and microfilaria. Sequence and phylogenetic analysis revealed that S. equina isolated in the current study from donkeys in Egypt (accession no., MH345965) shared 100% identity with isolates from horse and man in Italy and Iran, respectively and clustered in the same clade with S. digitata, S. tundra and S. labiatopapillosa. Conclusions: Identification with light microscopy lacked the ability to characterize different Setaria species, and so using scanning electron microscopy is considered a good choice to distinguish the ultrastructures. In addition, performing the phylogenetic analysis was necessary to detect relationships between different filarial worms, which could not detect by the morphological characterization of adult worms.