Infection and transmission heterogeneity of a multi-host pathogen (Batrachochytrium dendrobatidis) within an amphibian community

The majority of parasites infect multiple hosts. As the outcome of the infection is different in each of them, most studies of wildlife disease focus on the few species that suffer the most severe consequences. However, the role that each host plays in the persistence and transmission of infection can be crucial to understanding the spread of a parasite and the risk it poses to the community. Current theory predicts that certain host species can modulate the infection in other species by amplifying or diluting both infection prevalence and infection intensity, both of which have implications for disease risk within those communities. The fungus Batrachochytrium dendrobatidis (Bd), the causal agent of the disease chytridiomycosis, has caused global amphibian population declines and extinctions. However, not all infected species are affected equally, and thus Bd is a good example of a multi-host pathogen that must ultimately be studied with a community approach. To test whether the common midwife toad Alytes obstetricans is a reservoir and possible amplifier of infection of other species, we used experimental approaches in captive and wild populations to determine the effect of common midwife toad larvae on infection of other amphibian species found in the Peñalara Massif, Spain. We observed that the most widely and heavily infected species, the common midwife toad, may be amplifying the infection loads in other species, all of which have different degrees of susceptibility to Bd infection. Our results have important implications for performing mitigation actions focused on potential ‘amplifier’ hosts and for better understanding the mechanisms of Bd transmission.Peer reviewe

Localised Badger Culling Increases Risk of Herd Breakdown on Nearby, Not Focal, Land

Bovine tuberculosis is an important disease affecting the UK livestock industry. Controlling bovine tuberculosis (TB) is made more complex by the presence of a wildlife host, the Eurasian badger, Meles meles. Repeated large-scale badger culls implemented in the Randomised Badger Culling Trial (RBCT) were associated with decreased cattle risks inside the culling area, but also with increased cattle risks up to the 2km outside the culling area. Intermediate reductions in badger density, as achieved by localised reactive culling in the RBCT, significantly increased cattle TB. Using a matched-pairs case-control study design (n = 221 pairs of cattle herds), we investigated the spatial scale over which localised badger culling had its biggest impact. We found that reactive badger culling had a significant positive association with the risk of cattle TB at distances of 1-3km and 3-5km, and that no such association existed over shorter distances (<1km). These findings indicate that localised badger culls had significant negative effects, not on the land on which culling took place, but, perhaps more importantly, on adjoining lands and farms

Host species vary in infection probability, sub-lethal effects, and costs of immune response when exposed to an amphibian parasite

The amphibian parasite Batrachochytrium dendrobatidis (Bd) is regarded as an extreme generalist, infecting over 500 species, but amongst these hosts there exists a great deal of variation in the susceptibility to and the costs of parasite exposure. We use two infection experiments to determine whether inter-specific variation in the sublethal and lethal effects of parasite exposure exist in two host species. We then tested the relative roles of host density and diversity on infection probability of a focal susceptible host. Our results show significant heterogeneity in host species response to parasite exposure, and that both lethal and sub-lethal costs exist in individuals that are able to resist infection, indicating that successful immune response to infection comes at a cost. Further, we show that increasing host density significantly increased the likelihood of susceptible individuals becoming infected with Bd irrespective of host diversity and variation in host susceptibility. These results suggest that populations of resistant species are likely to suffer ill-effects of exposure to Bd regardless of their infection status, and that at the stage of initial infection there was no support for the dilution of transmission events, in contrast to other studies that focus on subsequent transmission of infection

Host contribution to parasite persistence is consistent between parasites and over time, but varies spatially

Most parasites and pathogens infect multiple hosts, but a great deal of variation exists in the role of those hosts in persistence of infection. Understanding which hosts are most important in maintaining parasites can provide a clearer target for infection control. Recently developed empirical and theoretical approaches provide a way to quantify the relative contribution of hosts within a community and place them in a multihost framework to better direct control efforts. Amphibians provide a framework for better understanding multihost‐multiparasite dynamics. Two well‐studied amphibian parasites, Bd and Ranavirus, infect multiple host species and exhibit a great deal of heterogeneity in how they affect hosts. We used these two parasites and a community of 5 amphibian species to investigate the relative importance of hosts in parasite persistence, and how any patterns varied spatially and temporally. At two sites (Lake Ercina and Lake Lloroza in the Picos de Europa National Park) we collected data on the prevalence and shedding rate of parasite infection for both Bd and Ranavirus, and the abundance of each species’ life‐stages. We used these data to parameterise a recently developed modelling framework, which was used to quantify the relative contribution of each host to the community reproductive number, R0. By comparing each host category over time and between sites we were able to identify consistencies in which host was responsible for the maintenance of these two parasites. Within a site one species consistently contributed the most to the persistence of both parasites. This consistency did not transfer between sites, the maintenance host species being different for each. At one site (Ercina) life‐stages of the common midwife toad, Alytes obstetricans, acted as the maintenance host for both Bd and Ranavirus. In contrast, at the second site, Lloroza, the alpine newt, Ichthyosaura alpestris, fulfilled that role. A single host species was responsible for infection persistence of both parasites at each lake. Attempts to control the infection levels and impacts of multiple parasites can benefit from a community epidemiology approach, and provide clarity on which hosts are the foci of mitigation efforts. However, at a small spatial‐scale the target host may vary according to the physical qualities of those sites and the demographics of the host community

X-Ray Groups of Galaxies in the Aegis Deep and Wide Fields

We present the results of a search for extended X-ray sources and their corresponding galaxy groups from 800-ks Chandra coverage of the All-wavelength Extended Groth Strip International Survey (AEGIS). This yields one of the largest X-ray selected galaxy group catalogs from a blind survey to date. The red-sequence technique and spectroscopic redshifts allow us to identify 100$$ of reliable sources, leading to a catalog of 52 galaxy groups. The groups span the redshift range $z\sim0.066-1.544$ and virial mass range $M_{200}\sim1.34\times 10^{13}-1.33\times 10^{14}M_\odot$. For the 49 extended sources which lie within DEEP2 and DEEP3 Galaxy Redshift Survey coverage, we identify spectroscopic counterparts and determine velocity dispersions. We select member galaxies by applying different cuts along the line of sight or in projected spatial coordinates. A constant cut along the line of sight can cause a large scatter in scaling relations in low-mass or high-mass systems depending on the size of cut. A velocity dispersion based virial radius can more overestimate velocity dispersion in comparison to X-ray based virial radius for low mass systems. There is no significant difference between these two radial cuts for more massive systems. Independent of radial cut, overestimation of velocity dispersion can be created in case of existence of significant substructure and also compactness in X-ray emission which mostly occur in low mass systems. We also present a comparison between X-ray galaxy groups and optical galaxy groups detected using the Voronoi-Delaunay method (VDM) for DEEP2 data in this field.Comment: Accepted for publication in AP

Online classified adverts reflect the broader United Kingdom trade in turtles and tortoises rather than drive it

Online sales are increasingly a route by which exotic animals are sold in the global pet trade. There are numerous types of online platforms and transaction types, and dedicated classified advertisement sites are a popular means of buying and selling animals. Despite their large and increasing use, we have a relatively poor understanding of the number of, and taxonomic variation in, the animals sold online. This information may be key in efforts to optimise the welfare of the animals being sold, and the ethics and sustainability of the trade via that platform. To fill this knowledge gap, we monitored and analysed the advertisements of chelonians (turtles and tortoises) placed on one of the United Kingdom’s largest dedicated classified ads sites, www.pets4homes.co.uk, over the course of a year, from July 2020 until June 2021. We analysed temporal, taxonomic, and advertiser related trends in the volumes of advertisements placed and compared the prices and the sentiment of language within adverts for different species. We found that the species advertised, the prices requested, and infrequent use of the site by most advertisers is consistent with most adverts being for animals being resold by casual users. Further, we found that turtles were consistently advertised for lower prices and in multiples than tortoises, and that the language with which they were advertised was less positive. We conclude that on this website the online trade reflects the broader trade, rather than drives the sales of chelonians in the UK, and that any interventions aiming to improve welfare and sustainability would be better placed earlier in the supply chain

Drivers of Batrachochytrium dendrobatidis infection load, with evidence of infection tolerance in adult male toads (Bufo spinosus)

Chytridiomycosis is affecting hundreds of amphibian species worldwide, but while in tropical areas, adult individuals have been the focus of most investigations, the exact role played by infection intensity of breeding adults is not well understood in temperate areas. We conducted mark–recapture–capture surveys during spiny common toad breeding seasons from 2006 to 2018 at the site of the first recorded outbreak of chytridiomycosis in Europe, the Peñalara Massif (Sierra de Guadarrama National Park, central Spain), and collected infection samples and several variables related to the reproductive effort of male individuals. We used general linear mixed models to evaluate the contribution of study variables on the infection loads of adult male toads exhibited at their capturing date. We also analysed the differences on several male characteristics between the pond with the largest breeding population against the rest of the ponds. We found that the duration of time spent in the waterbody and the condition of the host predicted infection loads. Animals of good physical condition, that spent longer in water, have higher infection levels than individuals with the opposite set of traits. The pond supporting the largest breeding population housed smaller male toads and in poorer condition. Our results are consistent with a shift in reproductive strategy in response to infection and potentially a strategy of tolerance, rather than resistance to infection. These findings have applications for disease mitigation and theoretical implications related to the trade-offs made and the evolution of traits in response to the disease

The WIRCAM Deep Infrared Cluster Survey I: Groups and Clusters at z > 1.1

We use CFHTLS deep optical data, WIRCam Deep Survey (WIRDS) NIR data and XMM data to identify z>1.1 clusters in the CFHTLS D1 and D4 fields. Counterparts to such clusters can not be identified without deep NIR data and as such the total of =1deg2 of J , H & Ks band imaging provided by WIRDS is an indispensable tool in such work. Using public XMM X-ray data, we identify extended X-ray sources in the two fields. The resulting catalogue of extended X-ray sources was analyzed for optical/NIR counterparts, using a red-sequence algorithm. Redshifts of candidate groups and clusters were estimated using the median photometric redshifts of detected counterparts and where available spectroscopic data. Additionally, we surveyed X-ray point sources for potential group systems at the limit of our detection range in the X-ray data. A catalogue of z > 1.1 cluster candidates in the two fields has been compiled and cluster masses, radii and temperatures have been estimated using the scaling relations. The catalogue consists of 15 z > 1.1 candidates. Three of the detections are previously published extended X-ray sources. Of note is JKSC 041 for which we identify possible structures at z = 0.8, z = 0.96, z = 1.13 and z = 1.49. We also make an independent detection of the massive cluster, XMMXCS J2215.9-1738. We use the z > 1.1 catalogue to compare the cluster number counts in these fields with models based on WMAP 7-year cosmology and find that the models slightly over-predict the observations, whilst at z>1.5 we do not detect any clusters. We note that cluster number counts at z > 1.1 are highly sensitive to the cosmological model, however a significant reduction in present statistical (due to available survey area) and systematic (due to cluster scaling relations) uncertainties is required in order to confidently constrain cosmological parameters using cluster number counts at high redshift.Comment: 22 pages, 22 figures, Accepted 4 August 201