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Thread: AJC's Frogroom: Scientific literature update

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    Default AJC's Frogroom: Scientific literature update

    AJC's Frogroom (UK) November 13th, 2009 04:43 AM: Scientific literature update

    There's been some interesting work about chytrid published in the scientific literature recently, so I thought I'd do a roundup. You may not be able to access these papers, so I've added a one line take home message for each one:


    Global emergence of Batrachochytrium dendrobatidis and amphibian chytridiomycosis in space, time, and host. Ann Rev Microbiol. 2009;63:291-310
    Batrachochytrium dendrobatidis (Bd) is a chytrid fungus that causes chytridiomycosis in amphibians. Only named in 1999, Bd is a proximate driver of declines in global amphibian biodiversity. The pathogen infects over 350 species of amphibians and is found on all continents except Antarctica. However, the processes that have led to the global distribution of Bd and the occurrence of chytridiomycosis remain unclear. This review explores the molecular, epidemiological, and ecological evidence that Bd evolved from an endemic ancestral lineage to achieve global prominence via anthropogenically mediated spread. We then consider the major host and pathogen factors that have led to the occurrence of chytridiomycosis in amphibian species, populations, and communities.
    Summary: This is an important, state-of-the-art paper which summarizes all that we know (and don't know) about the epidemiology of chytrid.


    Pathogenesis of chytridiomycosis, a cause of catastrophic amphibian declines. Science. 2009 Oct 23;326(5952):582-5
    The pathogen Batrachochytrium dendrobatidis (Bd), which causes the skin disease chytridiomycosis, is one of the few highly virulent fungi in vertebrates and has been implicated in worldwide amphibian declines. However, the mechanism by which Bd causes death has not been determined. We show that Bd infection is associated with pathophysiological changes that lead to mortality in green tree frogs (Litoria caerulea). In diseased individuals, electrolyte transport across the epidermis was inhibited by >50%, plasma sodium and potassium concentrations were respectively reduced by approximately 20% and approximately 50%, and asystolic cardiac arrest resulted in death. Because the skin is critical in maintaining amphibian homeostasis, disruption to cutaneous function may be the mechanism by which Bd produces morbidity and mortality across a wide range of phylogenetically distant amphibian taxa.
    Summary: This paper caused a bit of a splash in the popular press and I'm not sure why, because these findings aren't really that new, but it's still an important piece of work.


    Distribution limits of Batrachochytrium dendrobatidis: a case study in the Rocky Mountains, USA. J Wildl Dis. 2009 Oct;45(4):1198-202
    Knowledge of the environmental constraints on a pathogen is critical to predicting its dynamics and effects on populations. Batrachochytrium dendrobatidis (Bd), an aquatic fungus that has been linked with widespread amphibian declines, is ubiquitous in the Rocky Mountains. As part of assessing the distribution limits of Bd in our study area, we sampled the water column and sediments for Bd zoospores in 30 high-elevation water bodies that lacked amphibians. All water bodies were in areas where Bd has been documented from neighboring, lower-elevation areas. We targeted areas lacking amphibians because existence of Bd independent of amphibians would have both ecologic and management implications. We did not detect Bd, which supports the hypothesis that it does not live independently of amphibians. However, assuming a detection sensitivity of 59.5% (based on sampling of water where amphibians tested positive for Bd), we only had 95% confidence of detecting Bd if it was in > or =16% of our sites. Further investigation into potential abiotic reservoirs is needed, but our results provide a strategic step in determining the distributional and environmental limitations of Bd in our study region.
    Summary: Fairly self-explanatory - no amphibians, no chytrid.


    First detection of the amphibian chytrid fungus Batrachochytrium dendrobatidis in free-ranging populations of amphibians on mainland Asia: survey in South Korea. Dis Aquat Organ. 2009 Sep 7;86(1):9-13
    Chytridiomycosis, a disease that has caused amphibian population declines globally and elevated many species of anurans to endangered or threatened status, has recently been declared an internationally notifiable disease. Batrachochytrium dendrobatidis (Bd), the amphibian chytrid fungus causing this disease, has not been previously reported in Korea or on mainland Asia. Thirty-six frog specimens representing 7 species were collected from the wild in South Korea and examined for Bd using standard PCR. Bd was detected in 14 (38.8%) samples from 3 species (Bufo gargarizans, Hyla japonica, and Rana catesbiana). Skin sections from all 14 PCR-positive frogs were examined using 2 staining techniques: haematoxylin and eosin (H&E) and Bd immunoperoxidase (IPX). In histological sections, zoosporangia were found in 6 frogs, with lower sensitivity for H&E (21%) than for IPX (46%). Intensity of infection, based on histopathology, was low in all frogs. These results confirm that Bd is present in South Korea and, hence, on the Asian mainland. Studies are urgently required to determine the impact of chytridiomycosis on Korean amphibians, and to map the distribution of Bd in Korea and other Asian mainland countries.
    Summary: Another small scale survey (many of these published now), hard to interpret what this means in bigger terms, other than "Chytrid is out there".





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