Rooney et al. Parasites Vectors (2021) 14:189 https://doi.org/10.1186/s13071-021-04688-4 Parasites & Vectors RESEARCH Open Access Vaccination against the brown stomach worm, Teladorsagia circumcincta, followed by parasite challenge, induces inconsistent modifcations in gut microbiota composition of lambs James Rooney1, Alba Cortés1,2†, Riccardo Scotti1†, Daniel R. G. Price3, Yvonne Bartley3, Karen Fairlie‑Clarke3, Tom N. McNeilly4, Alasdair J. Nisbet3 and Cinzia Cantacessi1* Abstract Background: Growing evidence points towards a role of gastrointestinal (GI) helminth parasites of ruminants in modifying the composition of the host gut fora, with likely repercussions on the pathophysiology of worm infec‑ tion 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 fndings. To this aim, in this study, we analysed quantitative and qualitative fuctuations in the fae‑ cal 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) unvac‑ cinated/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 diferences in the populations of bacteria afected by immunisation against and infection by T. circumcincta were detected when comparing data from the two trials. Nevertheless, the abundance of Prevotella spp. was signifcantly linked to helminth infection in both trials. Conclusions: Despite the largely conficting fndings between the two trials, our data revealed that selected gut microbial populations are consistently afected 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 infuenced by several intrinsic and extrinsic host‑, parasite‑ and environment‑related factors. Keywords: Teladorsagia circumcincta, Gastrointestinal helminth, Ruminant, Microbiome, Vaccine, Prevotella spp. *Correspondence: [email protected] †Alba Cortés and Riccardo Scotti contributed equally to this work 1 Department of Veterinary Medicine, University of Cambridge, Cambridge, UK Full list of author information is available at the end of the article © The Author(s) 2021. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. The Creative Commons Public Domain Dedication waiver (http:// creat iveco mmons. org/ publi cdoma in/ zero/1. 0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Rooney et al. Parasites Vectors (2021) 14:189 Page 2 of 13 Background can signifcantly impact the composition of the ruminant It has been estimated that, by 2050, the global human gut microbiota [22–25]. Te efects of worm-mediated population will exceed 9 billion and that such a dra- changes in gut microbiota composition on the host abil- matic growth will exacerbate the already strained abil- ity to mount efective immune responses against the ity to meet the increasing demand of meat and dairy invading parasites are yet to be fully explored. Never- products [1]; thus, to avoid a potential food security theless, in a recent study [25], we investigated the fuc- crisis, global eforts are directed towards improved live- tuations in faecal microbiota composition of lambs stock health management practices via disease preven- vaccinated against, and experimentally infected with, T. tion and control [2, 3]. Amongst infectious agents of circumcincta; immunisation was achieved by inoculation livestock, parasitic helminths are a leading cause of dis- of eight recombinant parasite antigens [25]. In this study, ease in ruminants, with severe repercussions on both qualitative and quantitative changes in faecal microbiota animal health and welfare, and production efciency [3, composition were associated mainly with parasite infec- 4]. Worldwide, such losses are estimated at US $3 bil- tion rather than with vaccination-induced immunity. lion annually because of the decreased feed conversion However, data reproducibility across independent stud- ratio, stock death and replacement and the costs linked ies and cohorts of helminth-infected animals is pivotal in to regular use of anthelmintics [5]. order to harness the potential benefts of gut microbiome Whilst control of worms of livestock heavily relies manipulation for parasite control [22, 26–28]. on administration of antiparasitic drugs, global emer- Recently, Nisbet et al. [16] compiled data from several gence of parasite strains resistant to all available classes independent in vivo trials to select a pair of recombinant of anthelmintics makes the use of parasiticides as a sole immunogens from the original eight-component vac- means of helminth control unsustainable. Tus, over the cine (i.e. a mutated form of a calcium-dependent apyrase last decades, signifcant research eforts have been chan- [mTci-APY-1] and an astacin-like metalloprotease derived nelled into the development of vaccines against parasitic from T. circumcincta [Tci-MEP-1]) whose administration nematodes of ruminants [6–13], with several promising had the most impact of each of the original eight antigens prototypes being developed [14–16]. Amongst these is a on reducing cumulative faecal egg counts (cFEC) post- recombinant vaccine against one of the most economi- challenge infection. Te present project builds on data cally important gastrointestinal (GI) helminths of small from these trials, as well as on fndings from Cortés et al. ruminants in temperate regions, Teladorsagia circumci- [25], to investigate reproducibility of worm-microbiota ncta, which resides in the abomasum or ‘true stomach’ interaction studies using the Teladorsagia-sheep sys- [14, 17]. In particular, in a study by Nisbet et al. [14], tem. In particular, we utilise high-throughput amplicon a vaccine composed of eight recombinant helminth- sequencing of the bacterial 16S rRNA gene coupled with derived proteins administered to sheep prior to chal- bioinformatics and biostatistical analyses of sequence data lenge infection led to a reduction in T. circumcincta to explore the efect of vaccination against, and experi- faecal egg counts (FEC) and abomasal worm numbers mental infection with, T. circumcincta in two independ- by up to 75% compared with non-vaccinated controls. ent in vivo trials carried out over consecutive years under Te results of this and other studies [16, 18] show prom- largely similar experimental conditions. We show that, ise for the future use of vaccines as viable alternatives to whilst the full set of taxonomic changes in faecal micro- anthelmintics for parasite eradication; nevertheless, vac- biota composition of lambs infected with T. circumcincta cination studies published to date report varying ef- is inconsistent between trials, the relative abundance of cacy, thus suggesting that other immunity-independent, selected bacterial groups (e.g. Prevotella) are reproduc- unexplored factors may be contributing to parasite sur- ibly altered upon colonisation by this parasite and might vival within the host [5, 18]. A deeper understanding of therefore represent biomarkers of infection. the fundamental biology of the parasite and of the inter- actions between worm, host and gut environment might Materials and methods assist to enhance vaccine efcacy and/or to develop novel Experimental design, sample collection and molecular efective means of parasite control. biology procedures Amongst these interactions, the cross-talk among the Faecal samples analysed in this study were derived from parasites, host and resident gut fora is receiving increas- animals enrolled in two separate trials, conducted in 2017 ing attention, particularly due to the key roles of the ver- [16] and 2018 (A.J. Nisbet, unpublished data), respec- tebrate gut microbiome in immunity development and tively. Briefy, in each trial, 30 Texel crossbred lambs, defence against pathogens [19–21]. Indeed, over the fve to six months of age and helminth-free (verifed and last few years, a growing number of studies have pro- confrmed by parasitological examination of individual