Burrowes et al 2011 Toes vs Swabs

EcoHealth, 2016

Batrachochytrium dendrobatidis (Bd) is a pathogenic fungus which causes the disease chytridiomycosis in amphibians by infecting the animals' epidermis. The most commonly applied method for the detection of Bd is the use of a sterile swab, rubbed over the keratinized areas of an amphibian and then processed to yield DNA for detection by qPCR. This method has been used to infer a threshold of lethal infection in some species; however, how reliable and reproducible the swabbing method is at detecting the true burden of infection suffered by individuals is not known. European midwife toads, Alytes obstetricans, are susceptible to chytridiomycosis and are highly parasitised by Bd across Europe. By quantifying Bd-load throughout the entire skin and comparing this to swab results taken from the same individual, we determined whether epidermal swabs provide a quantifiable and accurate indication of the true fungal burden suffered. Further, we examined whether we could infer a threshold ...

Herpetological Review, 2014

2017

Emerging infectious diseases are increasingly recognized as key threats to wildlife. Batrachochytrium dendrobatidis (Bd), the causative agent of chytridiomycosis, has been implicated in mass mortalities, population declines, and local and global extinctions of many species of amphibians around the world. As such, it is currently the largest infectious disease threat to biodiversity. Understanding the distribution and spatial dynamics of Bd is crucial to predicting spread to new geographic areas, revealing the history of infection, and developing appropriate management strategies. One of the most striking features of Bd is the variability in outcome of infection that has been observed within a species, among populations. By identifying and comparing differences in variables that co-vary between populations exhibiting different infection characteristics, we can start to disentangle the mechanisms allowing for parasite persistence and proliferation. However, infection dynamics operate across nested levels of biological organization: within-host processes underlie among-host processes within a population. As such, this thesis works within the classical themes of spatial epidemiology to consider: 1) the distribution of Bd and the evidence for spatial heterogeneity in both the prevalence and intensity of infection, and 2) the role of individual-and population-level traits in defining infection outcome. The research presented, identifies that Bd functions endemically within Rana pipiens populations in Ontario. Outbreaks of chytridiomycosis are not observed, but infection dynamics show significant interannual fluctuations related to stable geographic factors and local climatic nuances experienced at particular host life history stages. However, v Rana pipiens also display variation in resistance to the pathogen, mediated by thermoregulation, dispersal behaviour, and phenotypic properties. Comparisons between host populations show variation in skin-associated bacterial communities, which may mediate susceptibility to chytridiomycosis. These bacterial communities are found to vary across latitude and between sites experiencing different levels of anthropogenic disturbance. Additionally, individual level traits, such as amphibian body temperature and body size are reported to influence bacterial community. Hence, this research highlights the importance of considering context-dependent individual-and populationlevel environmental heterogeneity, when attempting to predict the infection risk of Bd.

Fungal Ecology, 2011

Conservation Biology, 2010

Chytridiomycosis is an emerging disease of amphibians caused by the chytrid fungus Batrachochytrium dendrobatidis (hereafter Bd) (Fisher et al. 2009). Chytridiomycosis is thought to be contributing significantly to global amphibian declines (Berger et al. 1998; Stuart et al. 2004; Skerratt et al. 2007). In the Neotropics the disease has spread in a wave-like fashion (Lips et al. 2008), and arrival at previously pathogen-free sites in this region results in mass mortalities and extinctions (Lips et al. 2008). Little is known, however, about the effects of Bd after population declines have occurred. In some places, Bd persists where it has invaded (Retallick et al. 2004). Thus, amphibians may evolve resistance to this novel pathogen such that the negative effects of Bd are attenuated over time. Murray et al. (2009) address this very important question. They used a multistate mark-recapture model to estimate survival of Bd-infected and Bd-free frogs (Litoria pearsoniana) in Queensland, where Bd has been present for 30 years. The use ofmark-recapturemethods is a clear improvement over earlier studies in which survival was estimated but did not account for imperfect detectability of animals in field studies (Faustino et al. 2004; Schmidt 2004). Murray et al. found that Bd causes a substantial reduction in survival. This matters because a reduction in adult survival can lead to amphibian population declines (Schmidt et al. 2005) and because it implies that Bd remains a dangerous pathogen, such that amphibian populations are unlikely to recover from population declines caused by Bd for many decades, if ever. Here, I point out that the apparent monthly survival estimates ofMurray et al.

Methods in Ecology and Evolution, 2012

A pathogen of great significance to amphibian populations is the chytrid fungus, Batrachochytrium dendrobatidis (Bd). It has been demonstrated as causing recent epizootics in wild populations and is also widely found in captive animals. It is listed as a notifiable disease within the pet, bait and food trade because of its risk of introduction into wild populations. Due to this status, there has been much emphasis on reliably identifying and quantifying the pathogens in amphibians. Quantitative polymerase chain reaction (qPCR) has served as the recent standard for identifying this pathogen's presence. Newer technologies have greatly improved these reactions enabling researchers to use smaller volumes and run the reactions in less time. These 'fast' qPCR chemistries are gaining popularity because the reduced volumes required to run the reactions can save funding resources and reduce the time to data acquisition. 2. In this study, we compare the results from differing reaction methodologies using the same DNA extracts from pathogens collected from wild sampled amphibians. In addition to comparing the standard methodology and fast methodology for both pathogens, we also conducted a reduced volume methodology using the standard TaqMan chemistry for Bd. Estimated pathogen loads from 114 field swab samples were compared among methodologies. 3. We found that for Bd, all three methodologies produced similar results for prevalence (presence/absence) estimates. In terms of estimating pathogen loads in the samples, both the standard and fast methodologies produced comparable estimates but the reduced volume methodology exhibited significantly lower values. 4. Therefore, it appears that the fast methodology is adequate for use with Bd, and potentially several other wildlife pathogens, in estimating both prevalence and quantity, but the reduced volume methodology is inadequate and not recommended for use in quantifying samples.

Diversity and Distributions, 2013

Aim In a highly endemic, threatened amphibian assemblage, we measure and describe the geographic and taxonomic distribution of the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), with a view to identifying those sites and species most at risk of infection and its negative consequences. Additionally, we aimed to determine the potential for direct transmission events between two known carriers of Bd infection.

Chytridiomycosis, a disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is driving amphibian declines and extinctions in protected areas globally. The introduction of invasive reservoir species has been implicated in the spread of Bd but does not explain the appearance of the pathogen in remote protected areas. In the high elevation (.1500 m) Sierra Nevada of California, the native Pacific chorus frog, Pseudacris regilla, appears unaffected by chytridiomycosis while sympatric species experience catastrophic declines. We investigated whether P. regilla is a reservoir of Bd by comparing habitat occupancy before and after a major Bd outbreak and measuring infection in P. regilla in the field, monitoring susceptibility of P. regilla to Bd in the laboratory, examining tissues with histology to determine patterns of infection, and using an innovative soak technique to determine individual output of Bd zoospores in water. Pseudacris regilla persists at 100% of sites where a sympatric species has been extirpated from 72% in synchrony with a wave of Bd. In the laboratory, P. regilla carried loads of Bd as much as an order of magnitude higher than loads found lethal to sympatric species. Histology shows heavy Bd infection in patchy areas next to normal skin, a possible mechanism for tolerance. The soak technique was 77.8% effective at detecting Bd in water and showed an average output of 68 zoospores per minute per individual. The results of this study suggest P. regilla should act as a Bd reservoir and provide evidence of a tolerance mechanism in a reservoir species.

Biological Conservation, 2017

The impacts of pathogen emergence in naïve hosts can be catastrophic, and pathogen spread now ranks as a major threat to biodiversity. However, pathogen impacts can persist for decades after epidemics and produce variable host outcomes. Chytridiomycosis in amphibians (caused by the fungal pathogen Batrachochytrium dendrobatidis, Bd) is an exemplar, with impacts ranging from rapid population crashes and extinctions, to population declines and subsequent recoveries. Here, we investigate long-term impacts associated with chytridiomycosis in Australia. We conducted a continent-wide assessment of the disease, reviewing data collected since the arrival of Bd in about 1978, to assess and characterize mechanisms driving past, present and future impacts. We found chytridiomycosis to be implicated in the extinction or decline of 43 of Australia's 238 amphibian species. Population trajectories of declined species are highly variable; six species are experiencing ongoing declines, eight species are apparently stable and 11 species are recovering. Our results highlight that while some species are expanding, Bd continues to threaten species long after its emergence. Australian case-studies and synthesis of the global chytridiomycosis literature suggests that amphibian reservoir hosts are associated with continued declines in endemically infected populations, while population stability is promoted by environmental conditions that restrict Bd impact, and maintenance of high recruitment capacity that can offset mortality. Host genetic adaptation or decreased pathogen virulence may facilitate species recovery, but neither has been empirically demonstrated. Understanding processes that influence Bd-host dynamics and population persistence is crucial for assessing species extinction risk and identifying strategies to conserve disease-threatened species.

PLoS ONE, 2013

The rapid worldwide emergence of the amphibian pathogen Batrachochytrium dendrobatidis (Bd) is having a profound negative impact on biodiversity. However, global research efforts are fragmented and an overarching synthesis of global infection data is lacking. Here, we provide results from a community tool for the compilation of worldwide Bd presence and report on the analyses of data collated over a four-year period. Using this online database, we analysed: 1) spatial and taxonomic patterns of infection, including amphibian families that appear over-and under-infected; 2) relationships between Bd occurrence and declining amphibian species, including associations among Bd occurrence, species richness, and enigmatic population declines; and 3) patterns of environmental correlates with Bd, including climate metrics for all species combined and three families (Hylidae, Bufonidae, Ranidae) separately, at both a global scale and regional (U.S.A.) scale. These associations provide new insights for downscaled hypothesis testing. The pathogen has been detected in 52 of 82 countries in which sampling was reported, and it has been detected in 516 of 1240 (42%) amphibian species. We show that detected Bd infections are related to amphibian biodiversity and locations experiencing rapid enigmatic declines, supporting the hypothesis that greater complexity of amphibian communities increases the likelihood of emergence of infection and transmission of Bd. Using a global model including all sampled species, the odds of Bd detection decreased with increasing temperature range at a site. Further consideration of temperature range, rather than maximum or minimum temperatures, may provide new insights into Bd-host ecology. Whereas caution is necessary when interpreting such a broad global dataset, the use of our pathogen database is helping to inform studies of the epidemiology of Bd, as well as enabling regional, national, and international prioritization of conservation efforts. We provide recommendations for adaptive management to enhance the database utility and relevance.