Abstract
Haemonchus contortus and Teladorsagia circumcincta are among the two most pathogenic internal parasitic nematodes infecting small ruminants, such as sheep and goats, and are a global animal health issue. Accurate identification and delineation of Haemonchidae species is essential for development of diagnostic and control strategies with high resolution for Trichostrongyloidea infection in ruminants. Here, we describe in detail and compare the complete mitochondrial (mt) genomes of the New Zealand H. contortus and T. circumcincta field strains to improve our understanding of species- and strain-level evolution in these closely related roundworms. In the present study, we performed extensive comparative bioinformatics analyses on the recently sequenced complete mt genomes of the New Zealand H. contortus NZ_Hco_NP and T. circumcincta NZ_Teci_NP field strains. Amino acid sequences inferred from individual genes of each of the two mt genomes were compared, concatenated and subjected to phylogenetic analysis using Bayesian inference (BI), Maximum Likelihood (ML), and Maximum Parsimony (MP). The AT-rich mt genomes of H. contortus NZ_Hco_NP and T. circumcincta NZ_Teci_NP are 14,001 bp (A+T content of 77.4%) and 14,081 bp (A+T content of 77.3%) in size, respectively. All 36 of the typical nematode mt genes are transcribed in the forward direction in both species and comprise of 12 protein-encoding genes (PCGs), 2 ribosomal RNA (rrn) genes, and 22 transfer RNA (trn) genes. The secondary structures for the 22 trn genes and two rrn genes differ between H. contortus NZ_Hco_NP and T. circumcincta NZ_Teci_NP, however the gene arrangements of both are consistent with other Trichostrongylidea sequenced to date. Comparative analyses of the complete mitochondrial nucleotide sequences, PCGs, A+T rich and non-coding repeat regions of H. contortus NZ_Hco_NP and T. circumcincta NZ_Teci_NP further reinforces the high levels of diversity and gene flow observed among Trichostrongylidea, and supports their potential as ideal markers for strain-level identification from different hosts and geographical regions with high resolution for future studies. The complete mt genomes of H. contortus NZ_Hco_NP and T. circumcincta NZ_Teci_NP presented here provide useful novel markers for further studies of the meta-population connectivity and the genetic mechanisms driving evolution in nematode species.
Highlights
IntroductionH. contortus (barber’s pole worm) and T. circumcincta (brown stomach worm), are the most economically important pathogenic nematodes infecting small ruminants (sheep and goats) worldwide
H. contortus and T. circumcincta, are the most economically important pathogenic nematodes infecting small ruminants worldwide
The reconstruction of partial and complete mitochondrial genomes is becoming increasingly cost-effective with the advent of next-generation sequencing technology and recent advances in molecular parasitology tools, in particular for species identification and population genetics studies (Hu and Gasser, 2006; Jex et al, 2009)
Summary
H. contortus (barber’s pole worm) and T. circumcincta (brown stomach worm), are the most economically important pathogenic nematodes infecting small ruminants (sheep and goats) worldwide These blood-feeding strongylid nematodes are orally transmitted via contaminated pasture to the host where they infect the fourth stomach (abomasum) reducing animal production and causing anemia, edema, and associated complications often leading to death (Vlassoff et al, 2001; Sutherland and Scott, 2010). These parasites can be managed using existing prophylactic drugs (anthelmintics), their remarkable natural tendency to develop resistance combined with the diminishing efficacy of compounds used, threatens the global livestock industry (Kaplan, 2004; Kaplan and Vidyashankar, 2012). Given the increase in availability of genomic information resources (Palevich et al, 2018), it is crucial for the management of parasitic diseases that readily accessible molecular tools are developed to enable end-users to determine which species is infecting which animal host
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