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21.
A sensitive and quantitative TaqMan assay for the causative agent of chytridiomycosis in amphibians (Batrachochytrium dendrobatidis) has been developed and is routinely used in diagnostic laboratories. We assessed whether the real time detection of the TaqMan assay was as sensitive as the detection of the PCR product by agarose gel electrophoresis and ethidium bromide staining. We found, for practical purposes, that gel-based detection of the diagnostic fragment produced by means of the TaqMan assay or by conventional PCR that used a different polymerase and reaction mix was as sensitive as the real-time detection of the TaqMan assay. We recommend the qualified use of conventional PCR amplification combined with agarose gel electrophoresis and ethidium bromide staining for studies where only prevalence data are required, funding for equipment is limited or the acquisition of a real-time system is not cost effective. 相似文献
22.
Sam Young Paul Whitehorn Lee Berger Lee F. Skerratt Rick Speare Stephen Garland Rebecca Webb 《PloS one》2014,9(9)
The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) has caused mass mortality leading to population declines and extinctions in many frog species worldwide. The lack of host resistance may be due to fungal immunosuppressive effects that have been observed when Bd is incubated with cultured lymphocytes, but whether in vivo host immunosuppression occurs is unknown. We used a broad range of hematologic and protein electrophoresis biomarkers, along with various functional tests, to assess immune competence in common green (Litoria caerulea) and white-lipped (L. infrafrenata) tree frogs experimentally infected with Bd. Compared with uninfected frogs, Bd infection in L. caerulea caused a reduction in immunoglobulin and splenic lymphocyte responses to antigenic stimulation with sheep red blood cells, along with decreased white blood cell and serum protein concentrations, indicating possible impaired immune response capability of Bd-infected frogs. This is the first in vivo study suggesting that infection with Bd causes multiple defects in systemic host immune function, and this may contribute to disease development in susceptible host species. Although L. infrafrenata failed to maintain Bd infection after exposure, white blood cell and serum globulin concentrations were lower in recovered frogs compared with unexposed frogs, but antigen-specific serum and splenic antibody, and splenic cellular, responses were similar in both recovered and unexposed frogs. This may indicate potential systemic costs associated with infection clearance and/or redirection of host resources towards more effective mechanisms to overcome infection. No clear mechanism for resistance was identified in L. infrafrenata, suggesting that localized and/or innate immune defense mechanisms may be important factors involved in disease resistance in this species. 相似文献
23.
Sodium hypochlorite denatures the DNA of the amphibian chytrid fungus Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis, an aquatic amphibian fungus, has been implicated in many amphibian declines and extinctions. A real-time polymerase chain reaction (PCR) TaqMan assay is now used to detect and quantify B. dendrobatidis on amphibians and other substrates via tissue samples, swabbing and filtration. The extreme sensitivity of this diagnostic test makes it necessary to rigorously avoid cross-contamination of samples, which can produce false positives. One technique used to eliminate contamination is to destroy the contaminating DNA by chemical means. We tested 3 concentrations of sodium hypochlorite (NaOCl) (1, 6 and 12%) over 4 time periods (1, 6, 15 and 24 h) to determine if NaOCl denatures B. dendrobatidis DNA sufficiently to prevent its recognition and amplification in PCR tests for the fungus. Soaking in 12% NaOCl denatured 100% of DNA within 1 h. Six percent NaOCl was on average 99.999% effective across all exposure periods, with only very low numbers of zoospores detected following treatment. One percent NaOCl was ineffective across all treatment periods. Under ideal, clean conditions treatment with 6% NaOCl may be sufficient to destroy DNA and prevent cross-contamination of samples; however, we recommend treatment with 12% NaOCl for 1 h to be confident all B. dendrobatidis DNA is destroyed. 相似文献
24.
Robert Puschendorf Lauren Hodgson Ross A. Alford Lee F. Skerratt Jeremy VanDerWal 《Diversity & distributions》2013,19(10):1313-1321
Aim
Accurately documenting and predicting declines and shifts in species’ distributions is fundamental for implementing effective conservation strategies and directing future research; species distribution models (SDM) have become a powerful tool for such work. Nevertheless, much of the data used to create these models are opportunistic and often violate some of their basic assumptions. We use amphibian declines and extinctions linked to the fungus Batrachochytrium dendrobatidis (Bd) to examine how sampling biases in data collection can affect what we know of this disease and its effect on amphibians in the wild.Location
Queensland, Australia.Methods
We developed a distribution model for Bd incorporating known locality records for Bd and a subset of climatic variables that should correctly characterize its distribution. We tested this (original) model with additional surveys, recorded new Bd observations in novel environments and reran the distribution model. We then investigated the difference between the original and new models, and used frog abundance and infection status data from two of these new localities to look at the susceptibility of the torrent frog Litoria nannotis to chytridiomycosis.Results
While largely correct, the original SDM underestimated the distribution of Bd; sampling in ‘unsuitable’ drier environments discovered abundant populations of susceptible frogs with pathogen prevalences of up to 100%. The validation surveys further uncovered a new population of the frog Litoria lorica coexisting with the pathogen; this species was previously believed to be an extinct rain forest endemic.Main conclusion
Our results indicate that SDMs constructed using opportunistically collected data can be biased if species are not at equilibrium with their environment or because environmental gradients have not been adequately sampled. For disease ecology, the better estimations of pathogen distribution may lead to the discovery of new populations persisting at the edge of their range, which has important implications for the conservation of species threatened by chytridiomycosis.25.
Although mortality in 3 groups of 15 green tree frogs Litoria caerulea exposed to 3 isolates of Batrachochytrium dendrobatidis was 100%, time to death varied with isolate, highlighting the importance of strain and/or passage history in pathogenicity studies and possibly in the epidemiology of chytridiomycosis. A standard naming scheme for isolates of B. dendrobatidis is proposed. 相似文献
26.
Phillott AD Speare R Hines HB Skerratt LF Meyer E McDonald KR Cashins SD Mendez D Berger L 《Diseases of aquatic organisms》2010,92(2-3):175-185
Many of the recent global amphibian mass mortalities, declines and extinctions have been attributed to the emerging infectious disease chytridiomycosis. There have been mass mortalities due to ranaviral disease but no major declines or extinctions. Controlling the transmission and spread of disease is of utmost importance, especially where there is the potential for human involvement. We have reviewed current hygiene guidelines for working with wild frogs, identified potential flaws and recommended those most suitable and effective for the field environment. Our within-site hygiene measures aim to reduce the risk of transmission among individuals. These measures encompass the capture, handling and holding of amphibians, skin disinfection before and after invasive procedures, marking frogs, sealing open wounds and treatment of accessory equipment. Our between-site hygiene measures aim to mitigate the risk of pathogen spread among populations. We have designed a risk calculator to help simplify and standardise the decision-making process for determining the level of risk and appropriate risk mitigation strategies to reduce the risk of increasing pathogen spread above background levels. Calculation of an overall risk score for pathogen spread takes into account the prior activity of field workers, the proposed activity, remoteness of the site, presence of known pathogens and the consequences of increased pathogen spread for amphibians in a given area. 相似文献
27.
Chytridiomycosis is an emerging infectious disease caused by the pathogen Batrachochytrium dendrobatidis (Bd) and is the cause of the decline and extinction of amphibian species throughout the world. We surveyed the distribution of Bd within and around the Tasmanian Wilderness World Heritage Area (TWWHA), a 1.38 million ha area of significant fauna conservation value, which provides the majority of habitat for Tasmania's 3 endemic frog species (Litoria burrowsae, Bryobatrachus nimbus and Crinia tasmaniensis). Bd was detected at only 1 (3%) of the 33 sites surveyed within the TWWHA and at 15 (52%) of the 29 sites surveyed surrounding the TWWHA. The relatively low incidence of the disease within the TWWHA suggests that the majority of the TWWHA is currently free of the pathogen despite the fact that the region provides what appears to be optimal conditions for the persistence of Bd. For all survey sites within and around the TWWHA, the presence of Bd was strongly associated with the presence of gravel roads, forest and < 1000 m altitude--factors that in this study were associated with human-disturbed landscapes around the TWWHA. Conversely, the presence of walking tracks was strongly associated with the absence of Bd, suggesting an association of absence with relatively remote locations. The wide distribution of Bd in areas of Tasmania with high levels of human disturbance and its very limited occurrence in remote wilderness areas suggests that anthropogenic activities may facilitate the dissemination of the pathogen on a landscape scale in Tasmania. Because the majority of the TWWHA is not readily accessible and appears to be largely free of Bd, and because Tasmanian frogs reproduce in ponds rather than streams, it may be feasible to control the spread of the disease in the TWWHA. 相似文献
28.
Surveys were distributed to New Zealand land users in 1998 and 2008 to acquire information about New Zealand frogs with the aim of compiling and mapping their distribution and inferred population trends without costly and time-consuming field surveys. The overall frog population trend was reported as declining, with possible causes reported as an increase in agriculture, an increase in the distribution of predatory fish and disease. The resultant maps could be used for four main purposes: 1) to identify regions where Litoria populations are known to occur, which can be eliminated when considering suitable regions for translocation of Leiopelma; 2) to identify growing or stable populations of Litoria species, which may assist future disease surveys, population monitoring and to identify sources of genetic material that may serve as an Ark for declining Australian populations; 3) to highlight populations that are in decline to enable effective targeting of detailed disease studies; and 4) to approximate the stability of amphibian populations in the absence of more accurate, but costly, scientific monitoring. 相似文献
29.
Murray KA Rosauer D McCallum H Skerratt LF 《Proceedings. Biological sciences / The Royal Society》2011,278(1711):1515-1523
In studies of extinction risk, it is often insufficient to conclude that species with narrow ranges or small clutch sizes require prioritized protection. To improve conservation outcomes, we also need to know which threats interact with these traits to endanger some species but not others. In this study, we integrated the spatial patterns of key threats to Australian amphibians with species' ecological/life-history traits to both predict declining species and identify their likely threats. In addition to confirming the importance of previously identified traits (e.g. narrow range size), we find that extrinsic threats (primarily the disease chytridiomycosis and invasive mosquitofish) are equally important and interact with intrinsic traits (primarily ecological group) to create guild-specific pathways to decline in our model system. Integrating the spatial patterns of extrinsic threats in extinction risk analyses will improve our ability to detect and manage endangered species in the future, particularly where data deficiency is a problem. 相似文献
30.