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1.
Chytridiomycosis has been identified as a major cause of global amphibian declines. Despite widespread evidence of Batrachochytrium dendrobatidis infection in South African frogs, sampling for this disease has not focused on threatened species, or whether this pathogen poses a disease risk to these species. This study assessed the occurrence of Bd-infection in South African Red List species. In addition, all known records of infection from South Africa were used to model the ecological niche of Bd to provide a better understanding of spatial patterns and associated disease risk. Presence and prevalence of Bd was determined through quantitative real-time PCR of 360 skin swab samples from 17 threatened species from 38 sites across the country. Average prevalence was 14.8% for threatened species, with pathogen load varying considerably between species. MaxEnt was used to model the predicted distribution of Bd based on 683 positive records for South Africa. The resultant probability threshold map indicated that Bd is largely restricted to the wet eastern and coastal regions of South Africa. A lack of observed adverse impacts on wild threatened populations supports the endemic pathogen hypothesis for southern Africa. However, all threatened species occur within the limits of the predicted distribution for Bd, exposing them to potential Bd-associated risk factors. Predicting pathogen distribution patterns and potential impact is increasingly important for prioritising research and guiding management decisions.  相似文献   

2.
Probiotic therapy through bioaugmentation is a feasible disease mitigation strategy based on growing evidence that microbes contribute to host defences of plants and animals. Amphibians are currently threatened by the rapid global spread of the pathogen, Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis. Bioaugmentation of locally occurring protective bacteria on amphibians has mitigated this disease effectively in laboratory trials and one recent field trial. Areas still naïve to Bd provide an opportunity for conservationists to proactively implement probiotic strategies to prevent further amphibian declines. In areas where Bd is endemic, bioaugmentation can facilitate repatriation of susceptible amphibians currently maintained in assurance colonies. Here, we synthesise the current research in amphibian microbial ecology and bioaugmentation to identify characteristics of effective probiotics in relation to their interactions with Bd, their host, other resident microbes and the environment. To target at‐risk species and amphibian communities, we develop sampling strategies and filtering protocols that result in probiotics that inhibit Bd under ecologically relevant conditions and persist on susceptible amphibians. This filtering tool can be used proactively to guide amphibian disease mitigation and can be extended to other taxa threatened by emerging infectious diseases.  相似文献   

3.
Chytridiomycosis, caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), has been implicated in amphibian population declines worldwide. However, no amphibian declines or extinctions associated with Bd have been reported in Asia. To investigate the history of this pathogen in China, we examined 1,007 museum-preserved amphibian specimens of 80 species collected between 1933 and 2009. Bd was detected in 60 individuals (6.0%), with the earliest case of Bd infection occurring in one specimen of Bufo gargarizans and two Fejervarya limnocharis, all collected in 1933 from Chongqing, southwest China. Although mainly detected in non-threatened native amphibians, Bd was also found in four endangered species. We report the first evidence of Bd for Taiwan and the first detection of Bd in the critically endangered Chinese giant salamander (Andrias davidianus). Bd appears to have been present at a low rate of infection since at least the 1930s in China, and no significant differences in prevalence were detected between decades or provinces, suggesting that a historical steady endemic relationship between Bd and Chinese amphibians has occurred. Our results add new insights on the global emergence of Bd and suggest that this pathogen has been more widely distributed in the last century than previously believed.  相似文献   

4.
We performed a rapid response investigation to evaluate the presence and distribution of amphibian pathogens in Madagascar following our identification of amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd) and ranavirus in commercially exported amphibians. This targeted risk-based field surveillance program was conducted from February to April 2014 encompassing 12 regions and 47 survey sites. We simultaneously collected amphibian and environmental samples to increase survey sensitivity and performed sampling both in wilderness areas and commercial amphibian trade facilities. Bd was not detected in any of 508 amphibian skin swabs or 68 water filter samples, suggesting pathogen prevalence was below 0.8%, with 95% confidence during our visit. Ranavirus was detected in 5 of 97 amphibians, including one adult Mantidactylus cowanii and three unidentified larvae from Ranomafana National Park, and one adult Mantidactylus mocquardi from Ankaratra. Ranavirus was also detected in water samples collected from two commercial amphibian export facilities. We also provide the first report of an amphibian mass-mortality event observed in wild amphibians in Madagascar. Although neither Bd nor ranavirus appeared widespread in Madagascar during this investigation, additional health surveys are required to disentangle potential seasonal variations in pathogen abundance and detectability from actual changes in pathogen distribution and rates of spread. Accordingly, our results should be conservatively interpreted until a comparable survey effort during winter months has been performed. It is imperative that biosecurity practices be immediately adopted to limit the unintentional increased spread of disease through the movement of contaminated equipment or direct disposal of contaminated material from wildlife trade facilities. The presence of potentially introduced strains of ranaviruses suggests that Madagascar''s reptile species might also be threatened by disease. Standardized population monitoring of key amphibian and reptile species should be established with urgency to enable early detection of potential impacts of disease emergence in this global biodiversity hotspot.  相似文献   

5.
The fungal pathogen Batrachochytrium dendrobatidis (Bd) infects amphibians on every continent where they occur and is linked to the decline of over 200 amphibian species worldwide. At present, only three published Bd surveys exist for mainland Asia, and Bd has been detected in South Korea alone. In this article, we report the first survey for Bd in Peninsular Malaysia. We swabbed 127 individuals from the six amphibian families that occur on Peninsular Malaysia, including two orders, 27 genera, and 47 species. We detected Bd on 10 out of 127 individuals from four of five states and five of 11 localities, placing the 95% confidence interval for overall prevalence at 4–14%. We detected no variation in Bd prevalence among regions, elevations, or taxonomic groups. The infection intensity ranged from 1 to 157,000 genome equivalents. The presence of Bd infections in native species without clinical signs of disease suggests that Bd may be endemic to the region. Alternately, Bd may have been introduced from non-native amphibians because of the substantial amphibian food trade in Peninsular Malaysia. Under both scenarios, management efforts should be implemented to limit the spread of non-native Bd and protect the tremendous amphibian diversity in Peninsular Malaysia.  相似文献   

6.
The pathogenic fungus Batrachochytrium dendrobatidis (Bd) is a major conservation concern because of its role in decimating amphibian populations worldwide. We used quantitative PCR to screen 244 museum specimens from the Korean Peninsula, collected between 1911 and 2004, for the presence of Bd to gain insight into its history in Asia. Three specimens of Rugosa emeljanovi (previously Rana or Glandirana rugosa), collected in 1911 from Wonsan, North Korea, tested positive for Bd. Histology of these positive specimens revealed mild hyperkeratosis – a non-specific host response commonly found in Bd-infected frogs – but no Bd zoospores or zoosporangia. Our results indicate that Bd was present in Korea more than 100 years ago, consistent with hypotheses suggesting that Korean amphibians may be infected by endemic Asian Bd strains.  相似文献   

7.
Chytridiomycosis, an emerging infectious disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), has caused amphibian population declines worldwide. Bd was first described in the 1990s and there are still geographic gaps in the genetic analysis of this globally distributed pathogen. Relatively few genetic studies have focused on regions where Bd exhibits low virulence, potentially creating a bias in our current knowledge of the pathogen's genetic diversity. Disease-associated declines have not been recorded in Texas (USA), yet Bd has been detected on amphibians in the state. These strains have not been isolated and characterized genetically; therefore, we isolated, cultured, and genotyped Bd from central Texas and compared isolates to a panel of previously genotyped strains distributed across the Western Hemisphere. We also isolated other chytrids from east Texas not known to infect amphibians. To identify larval amphibian hosts, we sequenced part of the COI gene. Among 37 Bd isolates from Texas, we detected 19 unique multi-locus genotypes, but found no genetic structure associated with host species, Texas localities, or across North America. Isolates from central Texas exhibit high diversity and genetically cluster with BdGPL isolates from the western U.S. that have caused amphibian population declines. This study genetically characterizes isolates of Bd from the south central U.S. and adds to the global knowledge of Bd genotypes.  相似文献   

8.
Aim Panzootic chytridiomycosis caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd) is the proximate cause of rapid amphibian declines across diverse biomes. While the origin of Bd remains unclear, increasingly the global trade in amphibians is associated with the spread of the infection. Global samples of Bd genotypes from previously unsampled regions are essential to test this hypothesis. In this paper, we present a study of the prevalence and phylogeny of Bd in both invasive and native amphibian species in markets and in the wild in ten provinces of China. Location China. Method We used a nested PCR assay to amplify the ribosomal internal transcribed spacer region of Bd followed by sequencing. Result Our results showed 246 of 2734 amphibians testing positive for Bd, with 157 positive samples in the wild (7.6%) and 89 in markets (13.5%). 30 haplotypes of Bd were identified, including 20 first detections. Introduced Lithobates catesbeianus had the highest prevalence of infection and the largest number of Bd haplotypes in both the wild and markets. Phylogenetic analysis based on 73 haplotypes (57 from Asia and 16 from other continents) showed that a unique, well‐supported, basal haplotype is present in Asia. Phylogeographical analyses revealed that some geographical structure exists amongst a subset of global haplotypes. Main conclusions Strains of the basal haplotype infected Babina pleuraden, an amphibian that is endemic to China, and Andrias japonicus, endemic to Japan, showing that Southeast Asia harbours a novel endemic lineage of amphibian‐associated Bd. Our data suggest that Bd in Asia pre‐dates the expansion of a globalized lineage of Bd, a finding that is indicative of a broader association of amphibians and chytrids than has previously been recognized. More genetic data from Bd isolates are needed to reveal the phylogenetic relationship of Bd in China compared to that found elsewhere.  相似文献   

9.
Dispersal and exposure to amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd) is not confined to the aquatic habitat, but little is known about pathways that facilitate exposure to wild terrestrial amphibians that do not typically enter bodies of water. We explored the possible spread of Bd from an aquatic reservoir to terrestrial substrates by the emergence of recently metamorphosed infected amphibians and potential deposition of Bd-positive residue on riparian vegetation in Cusuco National Park, Honduras (CNP). Amphibians and their respective leaf perches were both sampled for Bd presence and the pathogen was detected on 76.1% (35/46) of leaves where a Bd-positive frog had rested. Although the viability of Bd detected on these leaves cannot be discerned from our quantitative PCR results, the cool air temperature, closed canopy, and high humidity of this cloud forest environment in CNP is expected to encourage pathogen persistence. High prevalence of infection (88.5%) detected in the recently metamorphosed amphibians and frequent shedding of Bd-positive residue on foliage demonstrates a pathway of Bd dispersal between aquatic and terrestrial habitats. This pathway provides the opportunity for environmental transmission of Bd among and between amphibian species without direct physical contact or exposure to an aquatic habitat.  相似文献   

10.
We studied the historical prevalence of the invasive and pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd) among amphibians from the Bolivian Andes. Our aim was also to determine its geographic pattern of dispersion, and a potential host taxonomic signature. We collected frog tissue samples from nine museum collections covering a period from 1863 to 2005 and from the field during 2009–2016. Bd was diagnosed via quantitative PCR in 599 individuals of 17 genera and 54 species. We found an overall Bd prevalence of 41% among 44 species tested. The first incidence of Bd was from a Telmatobius culeus in 1863; this is the earliest report of detection for this pathogen in the world. Results reveal a non-random historical and geographical pattern of Bd occurrence and amphibian declines that suggests the presence of two different invasive strains, an ancient endemic and a more recent introduction. Prevalence of Bd increased significantly by the mid-1990s, particularly in the cloud-forests, and this is coincident with the timing of drastic amphibian declines. In contrast, amphibians occurring in drier altiplano habitats have persisted in spite of Bd presence. We hypothesize that the early 1990s, and the cloud-forests in central Bolivia were the center of an epidemic surge of Bd that took its toll on many species, especially in the genus Telmatobius. Further sampling of cloud-forest species, and ongoing genetic studies of Bd isolates from Bolivia should help resolve the history of this invasive pathogen and test hypotheses on the differential response of endangered hosts.  相似文献   

11.
Batrachochytrium dendrobatidis (Bd), the cause of chytridiomycosis, is a pathogenic fungus that is found worldwide and is a major contributor to amphibian declines and extinctions. We report results of a comprehensive effort to assess the distribution and threat of Bd in one of the Earth’s most important biodiversity hotspots, the Albertine Rift in central Africa. In herpetological surveys conducted between 2010 and 2014, 1018 skin swabs from 17 amphibian genera in 39 sites across the Albertine Rift were tested for Bd by PCR. Overall, 19.5% of amphibians tested positive from all sites combined. Skin tissue samples from 163 amphibians were examined histologically; of these two had superficial epidermal intracorneal fungal colonization and lesions consistent with the disease chytridiomycosis. One amphibian was found dead during the surveys, and all others encountered appeared healthy. We found no evidence for Bd-induced mortality events, a finding consistent with other studies. To gain a historical perspective about Bd in the Albertine Rift, skin swabs from 232 museum-archived amphibians collected as voucher specimens from 1925–1994 were tested for Bd. Of these, one sample was positive; an Itombwe River frog (Phrynobatrachus asper) collected in 1950 in the Itombwe highlands. This finding represents the earliest record of Bd in the Democratic Republic of Congo. We modeled the distribution of Bd in the Albertine Rift using MaxEnt software, and trained our model for improved predictability. Our model predicts that Bd is currently widespread across the Albertine Rift, with moderate habitat suitability extending into the lowlands. Under climatic modeling scenarios our model predicts that optimal habitat suitability of Bd will decrease causing a major range contraction of the fungus by 2080. Our baseline data and modeling predictions are important for comparative studies, especially if significant changes in amphibian health status or climactic conditions are encountered in the future.  相似文献   

12.
Chytridiomycosis, caused by the pathogenic fungus Batrachochytrium dendrobatidis (Bd), is one of the largest threats to wildlife and is putatively linked to the extirpation of numerous amphibians. Despite over a decade of research on Bd, conflicting results from a number of studies make it difficult to forecast where future epizootics will occur and how to manage this pathogen effectively. Here, we emphasize how resolving these conflicts will advance Bd management and amphibian conservation efforts. We synthesize current knowledge on whether Bd is novel or endemic, whether amphibians exhibit acquired resistance to Bd, the importance of host resistance versus tolerance to Bd, and how biotic (e.g. species richness) and abiotic factors (e.g. climate change) affect Bd abundance. Advances in our knowledge of amphibian–chytrid interactions might inform the management of fungal pathogens in general, which are becoming more common and problematic globally.  相似文献   

13.
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).  相似文献   

14.
Genomic studies of the amphibian-killing fungus (Batrachochytrium dendrobatidis, [Bd]) identified three highly divergent genetic lineages, only one of which has a global distribution. Bd strains within these linages show variable genomic content due to differential loss of heterozygosity and recombination. The current quantitative polymerase chain reaction (qPCR) protocol to detect the fungus from amphibian skin swabs targets the intergenic transcribed spacer 1 (ITS1) region using a TaqMan fluorescent probe specific to Bd. We investigated the consequences of genomic differences in the quantification of ITS1 from eight distinct Bd strains, including representatives from North America, South America, the Caribbean, and Australia. To test for potential differences in amplification, we compared qPCR standards made from Bd zoospore counts for each strain, and showed that they differ significantly in amplification rates. To test potential mechanisms leading to strain differences in qPCR reaction parameters (slope and y-intercept), we: a) compared standard curves from the same strains made from extracted Bd genomic DNA in equimolar solutions, b) quantified the number of ITS1 copies per zoospore using a standard curve made from PCR-amplicons of the ITS1 region, and c) cloned and sequenced PCR-amplified ITS1 regions from these same strains to verify the presence of the probe site in all haplotypes. We found high strain variability in ITS1 copy number, ranging from 10 to 144 copies per single zoospore. Our results indicate that genome size might explain strain differences in ITS1 copy number, but not ITS1 sequence variation because the probe-binding site and primers were conserved across all haplotypes. For standards constructed from uncharacterized Bd strains, we recommend the use of single ITS1 PCR-amplicons as the absolute standard in conjunction with current quantitative assays to inform on copy number variation and provide universal estimates of pathogen zoospore loads from field-caught amphibians.  相似文献   

15.
For the past 17 years, scientists have been compiling a list of amphibian species susceptible to infection by the amphibian‐killing chytrid fungus, Batrachochytrium dendrobatidis (Bd), all over the world, with >500 species infected on every continent except Antarctica (Olson et al. 2013 ). Where Bd has been found, the impacts on amphibians has been one of two types: either Bd arrives into a naïve amphibian population followed by a mass die‐off and population declines (e.g. Lips et al. 2006 ), or Bd is present at some moderate prevalence, usually infecting many species but at apparently nonlethal intensities for a long time. In this issue of Molecular Ecology, Rodriguez et al. ( 2014 ) discover that the Atlantic Coastal Forest of Brazil is home to two Bd lineages: the Global Pandemic Lineage (Bd‐GPL) – the strain responsible for mass die‐offs and population declines – and a lineage endemic to Brazil (Bd‐Bz). Even more surprising was that both lineages have been present in this area for the past 100 years, making these the oldest records of Bd infecting amphibians. The team also described a moderate but steady prevalence of ~20% across all sampled anuran families for over 100 years, indicating that Brazil has been in an enzootic disease state for over a century. Most amphibians were infected with Bd‐GPL, suggesting this lineage may be a better competitor than Bd‐Bz or may be replacing the Bd‐Bz lineage. Rodriguez et al. ( 2014 ) also detected likely hybridization of the two Bd lineages, as originally described by Schloegel et al. ( 2012 ).  相似文献   

16.
The amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), has been linked to amphibian declines and extinctions worldwide. The pathogen has been found on amphibians throughout eastern North America, but has not been associated with mass die-offs in this region. In this study, we conducted laboratory experiments on the effects of Bd infection in a putative carrier species, Lithobates pipiens, using two estimators of fitness: jumping performance and testes morphology. Over the 8-week study period, peak acceleration during jumping was not significantly different between infected and uninfected animals. Peak velocity, however, was significantly lower for infected animals after 8 weeks. Two measures of sperm production, germinal epithelium depth, and maximum spermatic cyst diameter, showed no difference between infected and uninfected animals. The width, but not length, of testes of infected animals was significantly greater than in uninfected animals. This study is the first to show effects on whole-organism performance of Bd infection in post-metamorphic amphibians, and may have important long-term, evolutionary implications for amphibian populations co-existing with Bd infection.  相似文献   

17.
Although the chytrid fungus Batrachochytrium dendrobatidis (Bd), the etiological agent of amphibian chytridiomycosis, has been implicated in mass mortality and population declines on several continents around the world, there have been no reports on the presence of Bd infections in amphibians in China. We employed quantitative PCR and histological techniques to investigate the presence of Bd in introduced North American bullfrogs (Rana catesbeiana) (referred to hereafter as bullfrog) and native amphibians in bullfrog-invaded areas of the Yunnan Province, China. A total of 259 samples at five wild sites were collected between June and September in 2007 and 2008, including bullfrogs and four native amphibian species (Rana pleuraden, Rana chaochiaoensis, Odorrana andersonii, and Bombina maxima). In addition, 37 samples of adult bullfrogs were obtained from a food market. Bd infections were discovered in bullfrogs and three native amphibian species from all of the surveyed sites. Of the 39 Bd-positive samples, 35 were from wild-caught bullfrog tadpoles, postmetamorphic bullfrogs, R. pleuraden, R. chaochiaoensis, and O. andersonii, and four were from adult bullfrogs from the market. Our results provide the first evidence of the presence of Bd in Chinese amphibians, suggesting that native amphibian diversity in China is at risk from Bd. There is an urgent need to monitor the distribution of Bd in amphibians in China and understand the susceptibility of native amphibian species to chytridiomycosis. Strict regulations on the transportation of bullfrogs and the breeding of bullfrogs in markets and farms should be drafted in order to stop the spread of Bd by bullfrogs.  相似文献   

18.
Two species of Gliocephalotrichum were isolated from fallen fruits of the medicinal plant Terminalia chebula collected from the forests of Western Ghats, India. On the basis of morphological characters and ITS1–5.8S–ITS2 sequence similarity, the fungi have been identified as Gliocephalotrichum longibrachium and G. bulbilium. For the former species, this is the first report of its occurrence from India, whereas the latter, showing significant morphological variability, has been known previously from India.  相似文献   

19.
There is increasing evidence that the global spread of the fungal pathogen Batrachochytrium dendrobatidis (Bd) has been facilitated by the international trade in amphibians. Bd was first detected in the UK in 2004, and has since been detected in multiple wild amphibian populations. Most amphibians imported into the UK for the pet trade from outside the European Union enter the country via Heathrow Animal Reception Centre (HARC), where Bd-positive animals have been previously detected. Data on the volume, diversity and origin of imported amphibians were collected for 59 consignments arriving at HARC between November 2009 and June 2012, along with a surveillance study to investigate the prevalence of Bd in these animals. Forty-three amphibian genera were recorded, originating from 12 countries. It was estimated that 5000–7000 amphibians are imported through HARC into the UK annually for the pet trade. Bd was detected in consignments from the USA and Tanzania, in six genera, resulting in an overall prevalence of 3.6%. This suggests that imported amphibians are a source of Bd within the international pet trade.  相似文献   

20.
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