Population genetics study of Strongyloides fuelleborni and phylogenetic considerations on primate-infecting species of Strongyloides based on their mitochondrial genome sequences.

Strongyloides is a genus of parasitic nematodes of vertebrates comprising approximately 50 documented species, each with various host ranges. Among these, three species (S. stercoralis, S. fuelleborni, and S. cebus) are known to infect primate hosts. S. fuelleborni typically infects non-human primates in the Old World. To complement the existing information on the global genetic structure of this species, we conducted a genotyping study of S. fuelleborni samples collected from rhesus macaques in Myanmar, Japanese macaques in Japan, and some zoo-kept primates. This study identified a novel haplotype group in isolates from the Myanmar rhesus macaques. Subsequently, we obtained the complete or nearly complete mitochondrial genome sequences of S. fuelleborni, S. cebus (Strongyloides of New World monkeys), and S. vituli (Strongyloides of cattle). Phylogenetic analysis based on concatenated mitochondrial protein sequences of various Strongyloides species indicated a close relationship between S. fuelleborni, S. vituli and S. papillosus (Strongyloides in sheep and cattle). S. cebus is quite distantly related to both S. fuelleborni and S. stercoralis, which led to the hypothesis that the three primate Strongyloides species evolved independently as parasites of primates.

Phylogenetic relationships of Strongyloides species in carnivore hosts.

Strongyloides stercoralis is a parasitic nematode and a major pathogen responsible for human strongyloidiasis. The presence of this species in the dog population has led to an interest in studying the phylogenetic relationships among Strongyloides spp. in carnivore hosts. In the present study, Strongyloides spp. from various carnivore hosts (raccoon, Japanese badger, Siberian weasel, raccoon dog, masked palm civet, and domestic cat) were sought. Except for civets, Strongyloides spp. were identified in all host species. Based on 18S rDNA sequences, nine OTUs (operational taxonomy units) were identified. Molecular phylogenetic analyses using 18S28S rDNA and mitochondrial cox1 (cytochrome c oxidase subunit 1) sequences clustered them into two groups. The first group (named the stercoralis/procyonis group) was comprised of six OTUs and occurred in cats, raccoon dogs, raccoons (S. procyonis), Siberian weasels, and Japanese badgers and included S. stercoralis from humans and dogs. The second group (named the planiceps group) was made up of Strongyloides spp. from raccoon dogs (two OTUs) and one OTU from Siberian weasels. Subsequent analysis using almost the full-length nucleotide sequences of protein-coding genes in their mitochondrial genomes placed Strongyloides spp. of cats in a sister taxon position to S. stercoralis, whereas S. procyonis from raccoons was more distantly related to them. The presence of Strongyloides spp. from various carnivore hosts, which are close relatives of S. stercoralis, suggests this group of Strongyloides (the stercoralis/procyonis group) essentially evolved as parasites of carnivores, although more data on Strongyloides spp. from primate hosts are needed.

First molecular identification of Strongyloides vituli in cattle in Japan and insights into the evolutionary history of Strongyloides parasites of ruminants.

Traditionally, Strongyloides nematode infecting cattle had been thought to be a single species, S. papillosus. Surprisingly, Eberhardt et al. in 2008 reported two, rather than one Strongyloides species infected cattle, with one being S. papillosus and the other S. vituli. However, there was no subsequent report to support their findings. In July 2018, a case of a sudden death of a calf believed to be due to heavy infection with S. papillosus at a dairy farm in Miyazaki Prefecture, Japan, was reported. One month after the initiation of a deworming program to prevent further sudden deaths, fecal specimens from 24 cattle housed in the same barn were examined. Eight samples were positive for Strongyloides eggs. For species determination, the nucleotide sequences of 18S rDNA (small subunit ribosomal DNA gene), rpl-10 (ribosomal protein L10 gene), and mitochondrial (mt) cox1 (cytochrome c oxidase subunit 1 gene) were obtained. Typing data for all three marker genes indicated the presence of both species, S. papillosus and S. vituli, in the fecal samples. To our knowledge, this study is the first to support the original report by Eberhardt et al. regarding the sympatric existence of S. papillosus and S. vituli in cattle, and to report the presence of S. vituli in Japan. Interestingly, phylogenetic analyses of both rpl-10 and mt cox1 sequences indicated a closer genetic relationship of S. vituli with S. venezuelensis (Strongyloides of rats) than with S. papillosus, shedding light on the speciation history of Strongyloides nematodes.