The first genetic characterization of Setaria marshalli (Nematoda, Spirurida) with reliable DNA barcoding based on a mitochondrial genetic marker.

Setaria marshalli is a mosquito-borne filarial nematode that causes infection in calves younger than two years old. In the present study, nematodes were obtained from a calf in Japan and morphologically identified as S. marshalli. Additionally, the partial cytochrome oxidase subunit I (COI) region (596 bp) was analyzed for the first time to establish a reliable DNA barcode. Nucleotide sequences of COI were identical among the seven worms obtained. The COI region can be a useful marker for species discrimination in the case of S. marshalli since nucleotide variations observed between the closest congener, Setaria cervi (51/596 bp), were sufficient to allow species discrimination. However, the phylogenetic relationship of S. marshalli with its congeners was unclear in a maximum likelihood tree. We found that the partial COI sequence of S. marshalli analyzed in the present study matched a relevant section of the complete mitochondrial genome of S. labiatopapillosa that was deposited in the International Nucleotide Sequence Database. This finding suggests that S. marshalli was misdiagnosed as S. labiatopapillosa in a previous study. It is crucial to conduct accurate morphological analyses to obtain reliable molecular information regarding Setaria nematodes.