Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 1999
Publication Date: N/A
Interpretive Summary: Nematodirus battus continues to be recognized as a significant pathogen in European sheep, and was first recognized following a putative introduction into North America in 1985. Diagnostics and phylogenetic studies of Nematodirus and other gastrointestinal nematodes represent important cornerstones in effective control strategies. Molecular sequence data were used to infer phylogenetic relationships among N. battus and other species of Nematodirus, and to examine the geographic basis for genetic diversity in the former species. The resulting tree was consistent with caprine bovids as ancestral hosts for Nematodirus with a secondary host switch to bovids for N. helvetianus. Within N. battus, the lowest number of variable nucleotide sites was observed in samples representing apparently recent introductions to the United States and Canada, an observation consistent with a population bottleneck concomitant with translocation from Europe. The exact history of introduction and dissemination in North America remains to be elucidated. Molecular markers for diagnosis and identification of Nematodirus spp. can be based on amplification of the entire ITS region and application of 2 specific restriction endonucleases. Thus, the current study serves to further elucidate the history for N. battus and to provide the foundation for critical diagnostic capabilities for the identification of eggs, larvae and adult nematodes in cattle and sheep.
Nuclear ribosomal sequence data from the internal transcribed spacers (ITS-1 and ITS-2). 5.8S subunit, and regions of the 18S and 28 S genes were used to investigate sequence diversity among geographic samples of N. battus, and to infer phylogenetic relationships among Nematodirus species. Phylogenetic analysis of these data yielded strong support for relationships among species, and depicted N. helvetianus and N. spathiger as sister taxa, and a clade of these 2 species and N. filicollis. The tree is consistent with caprine bovids as ancestral hosts, with subsequent host shift to Bovinae in N. helvetianus. Eleven of 14 N. battus sequences were unique, with 19 variable sites among sequences representing 5 geographic samples. The lowest number of variable nucleotide sites was observed in samples representing apparently recent introductions to the United States and Canada, which is consistent with a population bottleneck concomitant with translocation. Comparison of directly sequenced PCR products and clones revelaed evidence for intraindividual variation at some of the sequence sites, and this pattern of variation and that within geographic samples indicates incomplete rDNA repeat homogenization within species. This pattern of variation is not conducive for inferring phylogenetic relationships among sequences representing N. battus, or addressing the putative history of introduction.