Non-invasive sampling methods for the detection of Batrachochytrium dendrobatidis in archived amphibians

Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, UK.
Diseases of Aquatic Organisms (Impact Factor: 1.75). 05/2009; 84(2):163-6. DOI: 10.3354/dao02029
Source: PubMed


Chytridiomycosis, an emerging infectious disease of amphibians caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), is associated with amphibian population declines worldwide. Investigation of the origin and spread of the pathogen requires examination of archived museum specimens of amphibians. Examination for Bd infection is usually done using histological techniques, which are often too destructive for valuable museum material. Three alternative methods for Bd detection (skin swabbing, brushing and scraping) were evaluated for ability to yield Bd DNA and destructiveness to specimens. Archived amphibians known to be Bd positive and which had been preserved in either formalin or ethanol for many years were used. Samples were analysed using a Bd-specific quantitative real-time Taqman PCR (qPCR) assay. There was no difference in the ability of each of the techniques to detect Bd infection, with the pathogen being detected in 75 to 81% of the 16 ethanol-fixed frogs examined. Visible evidence of sampling was left by scraping, but not by swabbing or brushing. The brush-qPCR technique detected higher counts of genomic equivalents than the other 2 sampling methods, although differences were not statistically significant. The qPCR assay did not detect Bd from any of the 6 formalin-fixed frogs examined, regardless of the sampling method. Nondestructive sampling techniques enable qPCR analysis of ethanol-preserved museum specimens for Bd. Recently, the incorporation of DNA cleanup steps allowed the detection of Bd in destructively sampled tissues from formalin preserved specimens. Further studies using nondestructive sampling incorporating DNA cleanup steps for the detection of Bd in formalin preserved specimens are warranted.

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    • "due to blemished preservation [e.g. 46], [106] or (iv) poor diagnostic assays, e.g. presence of PCR inhibitors [e.g. "
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    ABSTRACT: A putative driver of global amphibian decline is the panzootic chytrid fungus Batrachochytrium dendrobatidis (Bd). While Bd has been documented across continental Africa, its distribution in West Africa remains ambiguous. We tested 793 West African amphibians (one caecilian and 61 anuran species) for the presence of Bd. The samples originated from seven West African countries - Bénin, Burkina Faso, Côte d'Ivoire, Ghana, Guinea, Liberia, Sierra Leone - and were collected from a variety of habitats, ranging from lowland rainforests to montane forests, montane grasslands to humid and dry lowland savannahs. The species investigated comprised various life-history strategies, but we focused particularly on aquatic and riparian species. We used diagnostic PCR to screen 656 specimen swabs and histology to analyse 137 specimen toe tips. All samples tested negative for Bd, including a widespread habitat generalist Hoplobatrachus occipitalis which is intensively traded on the West African food market and thus could be a potential dispersal agent for Bd. Continental fine-grained (30 arc seconds) environmental niche models suggest that Bd should have a broad distribution across West Africa that includes most of the regions and habitats that we surveyed. The surprising apparent absence of Bd in West Africa indicates that the Dahomey Gap may have acted as a natural barrier. Herein we highlight the importance of this Bd-free region of the African continent - especially for the long-term conservation of several threatened species depending on fast flowing forest streams (Conraua alleni ("Vulnerable") and Petropedetes natator ("Near Threatened")) as well as the "Critically Endangered" viviparous toad endemic to the montane grasslands of Mount Nimba (Nimbaphrynoides occidentalis).
    Full-text · Article · Feb 2013 · PLoS ONE
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    • "Was it density dependent population dynamics [35]; climate shift [27], [29]; extreme weather events; or the invasion of novel Bd genotypes [21] Without clear bounds on the potential arrival date of Bd, elucidating the factors that interact with Bd to drive population collapse will continue to be fraught with uncertainty [36]. Quantification of Bd arrival dates is, thus, a clear priority, and applying the new Bd detection technologies [13], [34] in a systematic way to museum specimens is clearly an important direction in research on Bd and the amphibian declines in general. "
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    ABSTRACT: Pathogen spread can cause population declines and even species extinctions. Nonetheless, in the absence of tailored monitoring schemes, documenting pathogen spread can be difficult. In the case of worldwide amphibian declines the best present understanding is that the chytrid fungus Batrachochytrium dendrobatidis (Bd) has recently spread, causing amphibian declines and extinction in the process. However, good evidence demonstrating pathogen arrival followed by amphibian decline is rare, and analysis of putative evidence is often inadequate. Here we attempt to examine the relationship between Bd arrival and amphibian decline across north-eastern Australia, using sites where a wave-like pattern of amphibian decline was first noticed and at which intensive research has since been conducted. We develop an analytical framework that allows rigorous estimation of pathogen arrival date, which can then be used to test for a correlation between the time of pathogen arrival and amphibian decline across sites. Our results show that, with the current dataset, the earliest possible arrival date of Bd in north-eastern Australia is completely unresolved; Bd could have arrived immediately before sampling commenced or may have arrived thousands of years earlier, the present data simply cannot say. The currently available data are thus insufficient to assess the link between timing of pathogen arrival and population decline in this part of the world. This data insufficiency is surprising given that there have been decades of research on chytridiomycosis in Australia and that there is a general belief that the link between Bd arrival and population decline is well resolved in this region. The lack of data on Bd arrival currently acts as a major impediment to determining the role of environmental factors in driving the global amphibian declines, and should be a major focus of future research.
    Full-text · Article · Dec 2012 · PLoS ONE
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