Using a common commensal bacterium in endangered Takahe as a model to explore pathogen dynamics in isolated wildlife populations

A Systematic Review on the Role of Wildlife as Carriers and Spreaders of Campylobacter spp

Campylobacter spp. are important zoonotic pathogens and can cause one of the main bacterial diarrheal diseases worldwide. Research in the context of infection arising from transmission from other humans and other vertebrates has been extensive. A large fraction of these investigations has focused on domestic animals; however, there are also a number of publications which either totally, or at least in part, consider the role of wild or feral animals as carriers or spreaders of Campylobacter spp. Here, we carry out a systematic review to explore the role played by wild vertebrates as sources of Campylobacter spp. with a compilation of prevalence data for more than 150 species including reptiles, mammals and birds. We found that numerous vertebrate species can act as carriers of Campylobacter species, but we also found that some host specificity may exist, reducing the risk of spread from wildlife to domestic animals or humans.

Gut microbiota of the threatened takahē: biogeographic patterns and conservation implications

BACKGROUND

The Aotearoa New Zealand takahē (Porphyrio hochstetteri), once thought to be extinct, is a nationally threatened flightless rail under intensive conservation management. While there has been previous research into disease-related microbes in takahē, little is known about the microbes present in the gastrointestinal tract. Given the importance of gut-associated microbes to herbivore nutrition and immunity, knowledge of these communities is likely to be of considerable conservation value. Here we examined the gut microbiotas of 57 takahē at eight separate locations across Aotearoa New Zealand.

RESULTS

Faecal samples, taken as a proxy for the hindgut bacterial community, were subjected to 16S rRNA gene amplicon sequencing using Illumina MiSeq. Phylogenetic analysis of > 2200 amplicon sequence variants (ASVs) revealed nine main bacterial phyla (Acidobacteriota, Actinobacteriota, Bacteroidota, Campilobacterota, Firmicutes, Fusobacteriota, Planctomycetota, Proteobacteria, and Verrucomicrobiota) that accounted for the majority of sequence reads. Location was a significant effect (p value < 0.001, 9999 permutations) that accounted for 32% of the observed microbiota variation. One ASV, classified as Lactobacillus aviarius, was present in all samples at an average relative abundance of 17% (SD = 23.20). There was strong evidence (p = 0.002) for a difference in the abundance of the genus Lactobacillus between locations. A common commensal bacterium previously described in takahē, Campylobacter spp., was also detected in most faecal samples.

CONCLUSIONS

Location plays a pivotal role in the observed variation among takahē gut bacterial communities and is potentially due to factors such as supplemental feeding and medical treatment experienced by birds housed in captivity at one of the eight sampled sites. These data present a first glimpse of the previously unexplored takahē gut microbiota and provide a baseline for future microbiological studies and conservation efforts.

Our Current Understanding of Commensalism

Commensalisms, interactions between two species in which one species benefits and the other experiences no net effect, are frequently mentioned in the ecological literature but are surprisingly little studied. Here we review and synthesize our limited understanding of commensalism. We then argue that commensalism is not a single type of interaction; rather, it is a suite of phenomena associated with distinct ecological processes and evolutionary consequences. For each form of commensalism we define, we present evidence for how, where, and why it occurs, including when it is evolutionarily persistent and when it is an occasional outcome of interactions that are usually mutualistic or antagonistic. We argue that commensalism should be of great interest in the study of species interactions due to its location at the center of the continuum between positive and negative outcomes. Finally, we offer a roadmap for future research.

'Disperse abroad in the land': the role of wildlife in the dissemination of antimicrobial resistance

Antimicrobial resistance (AMR) has been detected in the microbiota of many wildlife species, including long-distance migrants. Inadequately treated wastes from humans and livestock dosed with antimicrobial drugs are often assumed to be the main sources of AMR to wildlife. While wildlife populations closely associated with human populations are more likely to harbour clinically important AMR related to that found in local humans and livestock, AMR is still common in remote wildlife populations with little direct human influence. Most reports of AMR in wildlife are survey based and/or small scale, so researchers can only speculate on possible sources and sinks of AMR or the impact of wildlife AMR on clinical resistance. This lack of quantitative data on the flow of AMR genes and AMR bacteria across the natural environment could reflect the numerous AMR sources and amplifiers in the populated world. Ecosystems with relatively simple and well-characterized potential inputs of AMR can provide tractable, but realistic, systems for studying AMR in the natural environment. New tools, such as animal tracking technologies and high-throughput sequencing of resistance genes and mobilomes, should be integrated with existing methodologies to understand how wildlife maintains and disperses AMR.

Genomic Epidemiology and Management of Salmonella in Island Ecosystems Used for Takahe Conservation

Translocation and isolation of threatened wildlife in new environments may have unforeseen consequences on pathogen transmission and evolution in host populations. Disease threats associated with intensive conservation management of wildlife remain speculative without gaining an understanding of pathogen dynamics in meta-populations and how location attributes may determine pathogen prevalence. We determined the prevalence and population structure of an opportunistic pathogen, Salmonella, in geographically isolated translocated sub-populations of an endangered New Zealand flightless bird, the takahe (Porphyrio hochstetteri). Out of the nine sub-populations tested, Salmonella was only isolated from takahe living on one private island. The apparent prevalence of Salmonella in takahe on the private island was 32% (95% CI 13-57%), with two serotypes, Salmonella Mississippi and Salmonella houtenae 40:gt-, identified. Epidemiological investigation of reservoirs on the private island and another island occupied by takahe identified environmental and reptile sources of S. Mississippi and S. houtenae 40:gt- on the private island. Single nucleotide polymorphism analysis of core genomes revealed low-level diversity among isolates belonging to the same serotype and little differentiation according to host and environmental source. The pattern observed may be representative of transmission between sympatric hosts and environmental sources, the presence of a common unsampled source, and/or evidence of a recent introduction into the ecosystem. This study highlights how genomic epidemiology can be used to ascertain and understand disease dynamics to inform the management of disease threats in endangered wildlife populations.

Microbial Genomics of a Host-Associated Commensal Bacterium in Fragmented Populations of Endangered Takahe

Isolation of wildlife into fragmented populations as a consequence of anthropogenic-mediated environmental change may alter host-pathogen relationships. Our understanding of some of the epidemiological features of infectious disease in vulnerable populations can be enhanced by the use of commensal bacteria as a proxy for invasive pathogens in natural ecosystems. The distinctive population structure of a well-described meta-population of a New Zealand endangered flightless bird, the takahe (Porphyrio hochstetteri), provided a unique opportunity to investigate the influence of host isolation on enteric microbial diversity. The genomic epidemiology of a prevalent rail-associated endemic commensal bacterium was explored using core genome and ribosomal multilocus sequence typing (rMLST) of 70 Campylobacter sp. nova 1 isolated from one third of the takahe population resident in multiple locations. While there was evidence of recombination between lineages, bacterial divergence appears to have occurred and multivariate analysis of 52 rMLST genes revealed location-associated differentiation of C. sp. nova 1 sequence types. Our results indicate that fragmentation and anthropogenic manipulation of populations can influence host-microbial relationships, with potential implications for niche adaptation and the evolution of micro-organisms in remote environments. This study provides a novel framework in which to explore the complex genomic epidemiology of micro-organisms in wildlife populations.

Network analysis of wildlife translocations in New Zealand

AIMS

To identify network measures with relevance to disease spread in a network of movements derived from the Department of Conservation (DOC) translocation records from 1970 to mid-2014, and to identify conservation sites that should be prioritised for surveillance activities and improvements to data collection to make the best use of network analysis techniques in the future.

METHODS

Data included the source and destination of translocated specimens, the species and the dates the translocations were expected to occur. The data were used to construct a directed, non-weighted network in which a translocation event represented a tie in the network. Network density, in-degree (movements entering a node of interest) and out-degree (movements leaving a node of interest) and reciprocity were calculated.

RESULTS

The data analysed consisted of 692 unique translocations between 307 sites, with the majority (518; 73%) being for birds. The constructed network for bird, reptile and frog translocations comprised 260 nodes, with 34/260 (13%) having two-way movements and 47/260 (18%) non-reciprocal movements. The median degree score (sum of in- and out-degree) was two (min 0, max 36) with a mean of 3.5 in a right skewed distribution. Most sites acted as receivers or senders of consignments with only a few having both high in- and high out-degree, and thus had characteristics that made them sites of interest for surveillance activities. These included the National Wildlife Centre at Mount Bruce, Tiritiri Matangi Island and Te Kakahu (Chalky Island).

CONCLUSIONS

The presence of linking sites that join larger clusters within the network creates the potential for rapid disease spread if a pathogen were to be introduced. The important sites that supply or receive specimens for translocations are already well recognised by those performing translocations in New Zealand, and this paper provides further information by quantifying their role within the network.