Molecular phylogeny of filarial worms (Nematoda: Filarioidea)

Abstract

No fewer than 33 species from 20 genera of filarial parasites (superfamily Filarioidea) have been recorded from various Malaysian vertebrates (amphibians, reptiles, birds, and mammals). Eight species worldwide are known to use humans as their definitive host and are the causative agents of human filariasis. Filariasis can also affect domestic and farm animals, such as dogs, cattle, and sheep. Although the filarial parasites have been extensively studied, some species remain dubious and studies on molecular phylogeny indicate that both the subfamilies Dirofilarriinae and Onchocercinae appear as polyphyletic groups. The phylogenetic relationships of 50 taxa of Filarioidea, comprising 49 taxa of Onchocercidae and one of Filariidae, were determined by the nucleotide sequences of cytochrome coxidase subunit I (COI) and 12S rDNA. Dracunculus medinensis (Dracunculoidea) and Thelazia callipaeda (Thelazioidea) were used as outgroups. In addition the concatenated sequences of 12 protein-coding genes (cox1-3, nad1-6, nad4L, cytb, and atp6) for nine taxa with complete mitochindrial genomes were studied. All species in this study could be differentiated by the genetic markers employed. The phylogenetic relationships of 50 taxa of Filarioidea based on COI, 12S rDNA and combined COI+12S rDNA nucleotide sequences in the present analysis do not support the family status for the genus Setaria. Members of Dirofi lariinae, Onchocercinae, and Splendidofi lariinae were not well resolved and indicated polyphyly for these subfamilies. It is evident that multiple genes and more taxa are needed to elucidate the phylogeny of filarial parasites. © National University of Singapore.