Comparative analysis of mitochondrial DNA datasets indicates that Toxascaris leonina represents a species complex

Abstract

Background Toxascaris leonina is one of the most common intestinal parasites of canids and felids. In this study, we characterised the entire mitochondrial (mt) genome sequence of T. leonina from the cheetah and compared it with that of T. leonina from the dog. Results The entire mt genome sequence of T. leonina from the cheetah is 14,685 bp in size, which is 375 bp longer than that from the dog, and it is 408 bp longer than that from the South China tiger. The overall nucleotide sequence (except for the non-coding region) identity was 92.8% between the two mt genomes of T. leonina from the cheetah and the dog. For the 12 protein-coding genes, sequence difference between T. leonina from the cheetah and the dog was 5.0–9.7% at the nucleotide level and 1.0–7.2% at the amino acid level. Moreover, comparison of mt cox 1 sequences among T. leonina isolates ( n = 23) from different hosts revealed substantial nucleotide differences (10.6%). Phylogenetic analysis showed the separation of T. leonina from canid and felid hosts into three distinct clades. Conclusions Taken together, these mtDNA datasets indicate that T. leonina from canid and felid hosts represents a species complex. Our results have implications for further studies of the molecular epidemiology, systematics and population genetics of this nematode. Electronic supplementary material The online version of this article (10.1186/s13071-019-3447-2) contains supplementary material, which is available to authorized users.

Characterization of the complete mitochondrial genome sequence of the dog roundwormToxascaris leonina(Nematoda, Ascarididae) from China

“…The maximum-likelihood (ML) phylogeny inferred from a concatenated amino acid dataset of 12 protein-coding genes from 32 nematode parasites clearly placed T. leonina together with other species from the family Ascarididae and separated from species of the families Toxocaridae, Anisakidae, and Ascaridiidae, with high bootstrap values (Figure 1). Within the genus Toxascaris of Ascarididae, two canid-originated T. leonina (one was from China and another was from Australia) clustered together, and were phylogenetically distinctive from felid-originated T. leonina (Chinese isolate), consistent with recent molecular studies (Fogt-Wyrwas et al 2019;Jin et al 2019), supporting that T. leonina may represent a species complex. Overall, the sequenced mitochondrial genome of T. leonina in this study adds novel molecular evidence for phylogenetic and taxonomic position of this roundworm species.…”

Molecular characterization of ascaridoid parasites from captive wild carnivores in China using ribosomal and mitochondrial sequences

“…It is clear that T. leonina is a cosmopolitan and polyxenical parasite in wild and domestic canids and felids [1]. However, recent studies by Fogt-Wyrwas et al [12], Jin et al [11] and Xie et al [61] consistently pointed out that T. leonina may be a species complex. Because combined molecular evidence from ribosomal nuclear DNA strongly showed the separation of T. leonina from different hosts into three distinct clades, i.e.…”

“…Like T. cati, the congenetic T. malaysiensis infects felids [10]. However, T. leonina is defined to infect both feline and canine species [11,12]. Humans are accidental hosts for Toxocara spp.…”

“…and Toxascaris spp. from dogs, cats and cattle [11,12,14,16,21,22]; importantly, such mtDNA-derived evidence supports the rDNA-based conclusion that T. malaysiensis is another valid ascaridoid species found in cats [23]. Nevertheless, considering that single rDNA or mtDNA loci only allow limited inference of molecular analyses [24] and that current sampling and studies mostly focus on domestic animal-originated Toxocara and Toxascaris [4,12], it would be essential and urgent to develop a combined analysis of nuclear and mitochondrial data for more accurate and robust branches in ascaridoids from a wider host-range that includes wild canids and felids.…”

“…Nevertheless, considering that single rDNA or mtDNA loci only allow limited inference of molecular analyses [24] and that current sampling and studies mostly focus on domestic animal-originated Toxocara and Toxascaris [4,12], it would be essential and urgent to develop a combined analysis of nuclear and mitochondrial data for more accurate and robust branches in ascaridoids from a wider host-range that includes wild canids and felids. Unfortunately, until now there has been still very limited molecular information available for these ascaridoids [11,12,14,25].…”