The parasitic nematode Strongyloides ratti exists as populations of long-lived asexual lineages

Abstract

Nematodes are important parasites of people and animals, and in natural ecosystems they are a major ecological force. Strongyloides ratti is a common parasitic nematode of wild rats and we have investigated its population genetics using single worm, whole genome sequencing. We find that S. ratti populations consist of mixtures of asexual lineages, widely dispersed across the host population. Genes that underly the parasitic phase of its life cycle are hyperdiverse, compared with the rest of the genome. These patterns of parasitic nematode population genetics have not been found before and may also apply to Strongyloides spp. that infect people.

The population genetics of Strongyloides papillosus in Pakistani goats revealed by whole genome sequencing

“…There has been previous population genomic analysis of Strongyloides . Specifically, S. ratti infecting wild rats in the UK was found to exist as a mixture of mainly asexual lineages parasites that were widely dispersed across the host population, findings that were consistent with earlier, UK-wide, studies (Fisher & Viney, 1998; Cole et al ., 2023).…”

“…The DNA extraction protocol is based on the method of Cole et al, 2023 but adapted for ethanol-stored worms after Zhou et al, 2019. Pools of larvae from each host were processed separately; pools of iL3s in ethanol were transferred into distilled water and then individual larvae were placed into wells of a 96 well plate, with each well containing 50 μL TE, which was then stored at -80 o C. Later, 70 μL of lysis buffer was added to each well, giving a final concentration of 200 mM NaCl,100 mM Tris-HCl (pH8.5), 50 mM EDTA (pH8), 0.5 % w/v SDS, 0.9 mg /mL Proteinase K, and 45 mM Dithiothreitol (DTT).…”

Advancing Strongyloides omics data: bridging the gap with Caenorhabditis elegans

“…Both studies found geographical clustering of the samples based on their genomes and little evidence of recombination, suggesting that the sexually reproducing free-living stage is rare in the wild populations. A population genomics study on S. ratti from wild rat faeces collected in England and Wales found that a few long-lived lines infect many rats across the three distinct sampling sites studies and there was little variation between the sites [48]. There is a strong positive selection pressure, with a high number of nonsynonymous SNPs, on gene families previously associated with Strongyloides parasitism in S. ratti (astacin-like metalloendopeptidases, CAP-domain containing proteins and acetylcholinesterases) [48].…”

“…A population genomics study on S. ratti from wild rat faeces collected in England and Wales found that a few long-lived lines infect many rats across the three distinct sampling sites studies and there was little variation between the sites [48]. There is a strong positive selection pressure, with a high number of nonsynonymous SNPs, on gene families previously associated with Strongyloides parasitism in S. ratti (astacin-like metalloendopeptidases, CAP-domain containing proteins and acetylcholinesterases) [48]. For all of these studies, only samples from a single geographical area (East Asia and the UK, respectively) are used so they are unlikely to be capturing all of the genetic diversity of either Strongyloides species.…”

Strongyloides : omics to worm-free populations

“…4) They may become female, and develop into autoinfective third-stage larvae (aiL3) within the host and re-infect the same host individual (autoinfective cycle, asexual). While all species of Strongyloides (but not necessarily all isolates of these species [22–24]) may undergo homogonic or heterogonic development, the autoinfective cycle (option 4) appears to be specific for S . stercoralis and maybe a few other less well-investigated species [18].…”