Vaccination against the brown stomach worm, Teladorsagia circumcincta, followed by parasite challenge, induces inconsistent modifications in gut microbiota composition of lambs

Abstract

Background Growing evidence points towards a role of gastrointestinal (GI) helminth parasites of ruminants in modifying the composition of the host gut flora, with likely repercussions on the pathophysiology of worm infection and disease, and on animal growth and productivity. However, a thorough understanding of the mechanisms governing helminth-microbiota interactions and of their impact on host health and welfare relies on reproducibility and replicability of findings. To this aim, in this study, we analysed quantitative and qualitative fluctuations in the faecal microbiota composition of lambs vaccinated against, and experimentally infected with, the parasitic GI nematode Teladorsagia circumcincta over the course of two separate trials performed over two consecutive years. Methods Two trials were conducted under similar experimental conditions in 2017 and 2018, respectively. In each trial, lambs were randomly assigned to one of the following experimental groups: (i) vaccinated/infected, (ii) unvaccinated/infected and (iii) unvaccinated/uninfected. Faecal samples collected from individual animals were subjected to DNA extraction followed by high-throughput sequencing of the V3-V4 region of the bacterial 16S rRNA gene and bioinformatics and biostatistical analyses of sequence data. Results Substantial differences in the populations of bacteria affected by immunisation against and infection by T. circumcincta were detected when comparing data from the two trials. Nevertheless, the abundance of Prevotella spp. was significantly linked to helminth infection in both trials. Conclusions Despite the largely conflicting findings between the two trials, our data revealed that selected gut microbial populations are consistently affected by T. circumcincta infection and/or vaccination. Nevertheless, our study calls for caution when interpreting data generated from in vivo helminth-microbiome interaction studies that may be influenced by several intrinsic and extrinsic host-, parasite- and environment-related factors.

Parasitic helminths and the host microbiome – a missing ‘extracellular vesicle-sized’ link?

“…Hence, it is highly conceivable that, besides mechanisms to communicate with host epithelial and immune cells [57], parasitic worms have also developed strategies to modulate the populations of microorganisms that share their niche inside the vertebrate host. Whilst substantial efforts have been directed towards understanding the impact that host microbiome alterations exert on helminth fitness and survival [12,13,[58][59][60], current knowledge of the consequences of worm establishment on the microbiome structure and function, as well as on the pathophysiology of helminth disease, remains scarce. Here, we propose that decoding the role(s) that helminth excretions/secretions, including EVs and their cargo molecules, play in modulating the host gut microbiota composition will assist elucidating the intricacies of helminth-host interactions.…”

“…Nevertheless, over the last decade, substantial evidence has emerged of the likely role of a third player in the crosstalk between vertebrate hosts and GI helminths, notably the host gut microbiota [12,13]. Indeed, several investigations conducted in helminth-infected humans and animals, under both experimental and natural conditions, have reported significant associations between parasite colonisation and shifts in the composition and/or function of the vertebrate gut microbiota, with likely repercussions on the pathophysiology of helminth infections, host immune responses and disease outcome (reviewed in [14]).…”

Worms and bugs of the gut: the search for diagnostic signatures using barcoding, and metagenomics–metabolomics

“…Examples include the characterization of the faecal microbiota of cohorts of human volunteers with coeliac disease or multiple sclerosis experimentally infected with N. americanus [137,145], and individuals naturally infected by STHs [142][143][144][145][146]. In relation to nematode species of veterinary importance, metabarcoding, using the bacterial 16S rRNA gene, has been applied to, for example, the characterization of the faecal microbiota of H. contortusinfected goats [147], T. circumcincta-infected sheep [148], or Ostertagia ostertagi-infected cattle [149].…”

“…Metabarcoding Nematoda DNA Gorillas, Mangabey MiSeq Illumina Larvae ITS-2 [114] Metagenomics Nematoda DNA Primate Hiseq Illumina Faeces 18S, COI [105] Metagenomics Nematoda, Platyhelminthes DNA Human MiSeq Illumina Faeces Unavailable [106] microbial profiles of helminth-infected humans and/or animals compared with corresponding uninfected hosts lead to contrasting results (reviewed in [129]), even between data sets generated from the same host-parasite pair under similar experimental conditions [148]. Such discrepancies are likely linked to variability in structure and composition of the vertebrate gut microbiota [130,134,150].…”

“…Furthermore, intrinsic and/or extrinsic factors, including, but not limited to, age, gender, diet and/ or underlying health conditions, all exert profound effects on the composition of the vertebrate gut microbiota [128,129,143]. Such inter-individual variability makes the discovery of reliable microbial-based biomarkers of helminth infection a challenging task; nevertheless, in a recent study, specific biomarker-discovery algorithms were applied to the identification of unique populations of faecal bacteria associated with worm colonization in T. circumcinctainfected sheep in an experimental system [148]. Whilst this study represents a promising step forward in the discovery of microbiota/microbiome-targeting biomarkers of helminth infections in both humans and animals, individual investigations examining the impact of worm colonization on gut microbial communities are often compromised by insufficient sample size and, thus, low statistical power [129].…”