Examining the Evidence for Chytridiomycosis in Threatened Amphibian Species (original) (raw)
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Amphibian Chytridiomycosis: A threat to global biodiversity
2014
Amphibians from all biogeographic regions of the world are faced with a significant decrease in their populations. Although the most common causes of this decline are undoubtedly the alteration and destruction of habitat, the influence of emerging diseases on species decline and extinction has also been shown in recent years. Such is the case of chytridiomycosis, an amphibian skin disease caused by the fungus Batrachochytrium dendrobatidis, which has drawn scientific attention as recent studies have attributed the extinction of more than 30 species in Latin America to its high pathogenicity and global distribution. In Mexico, the disease has already been identified in the Valley of Mexico and several states, such as Chiapas,
Amphibians from all biogeographic regions of the world are faced with a significant decrease in their populations. Although the most common causes of this decline are undoubtedly the alteration and destruction of habitat, the influence of emerging diseases on species decline and extinction has also been shown in recent years. Such is the case of chytridiomycosis, an amphibian skin disease caused by the fungus Batrachochytrium dendrobatidis, which has drawn scientific attention as recent studies have attributed the extinction of more than 30 species in Latin America to its high pathogenicity and global distribution. In Mexico, the disease has already been identified in the Valley of Mexico and several states, such as Chiapas, Estado de Mexico, Puebla, Oaxaca, Michoacan, Morelos, Sonora.. Yet further studies are necessary to increase our understanding of the behavior of chytridiomycosis in the wild and captive populations. As such, this review paper aims to advance our knowledge of this pathogen, its distribution and its worldwide and local control strategies.
Interventions for Reducing Extinction Risk in Chytridiomycosis-Threatened Amphibians
Conservation Biology, 2014
Wildlife diseases pose an increasing threat to biodiversity and are a major management challenge. A striking example of this threat is the emergence of chytridiomycosis. Despite diagnosis of chytridiomycosis as an important driver of global amphibian declines 15 years ago, researchers have yet to devise effective large scale management responses other than biosecurity measures to mitigate disease spread and the establishment of disease-free captive assurance colonies prior to or during disease outbreaks. We examined the development of management actions that can be implemented after an epidemic in surviving populations. We developed a conceptual framework with clear interventions to guide experimental management and applied research so that further extinctions of amphibian species threatened by chytridiomycosis might be prevented. Within our framework, there are 2 management approaches: reducing Batrachochytrium dendrobatidis (the fungus that causes chytridiomycosis) in the environment or on amphibians and increasing the capacity of populations to persist despite increased mortality from disease. The latter approach emphasizes that mitigation does not necessarily need to focus on reducing disease-associated mortality. We propose promising management actions that can be implemented and tested based on current knowledge and that include habitat manipulation, antifungal treatments, animal translocation, bioaugmentation, head starting, and selection for resistance. Case studies where these strategies are being implemented will demonstrate their potential to save critically endangered species.
Conservation Biology, 2009
Estimating disease-associated mortality and transmission processes is difficult in free-ranging wildlife but important for understanding disease impacts and dynamics and for informing management decisions. In a capture-mark-recapture study, we used a PCR-based diagnostic test in combination with multistate models to provide the first estimates of disease-associated mortality and detection, infection, and recovery rates for frogs endemically infected with the chytrid fungus Batrachochytrium dendrobatidis (Bd), which causes the pandemic amphibian disease chytridiomycosis. We found that endemic chytridiomycosis was associated with a substantial reduction (approximately 38%) in apparent monthly survival of the threatened rainforest treefrog Litoria pearsoniana despite a long period of coexistence (approximately 30 years); detection rate was not influenced by disease status; improved recovery and reduced infection rates correlated with decreased prevalence, which occurred when temperatures increased; and incorporating changes in individuals' infection status through time with multistate models increased effect size and support (98.6% vs. 71% of total support) for the presence of disease-associated mortality when compared with a Cormack-Jolly-Seber model in which infection status was restricted to the time of first capture. Our results indicate that amphibian populations can face significant ongoing pressure from chytridiomycosis long after epidemics associated with initial Bd invasions subside, an important consideration for the long-term conservation of many amphibian species worldwide. Our findings also improve confidence in estimates of disease prevalence in wild amphibians and provide a general framework for estimating parameters in epidemiological models for chytridiomycosis, an important step toward better understanding and management of this disease.
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.
Chytridiomycosis: a global threat to amphibians
Revue Scientifique Et Technique De L Office International Des Epizooties, 2013
Chytridiomycosis, which is caused by Batrachochytrium dendrobatidis, is an emerging infectious disease of amphibians. The disease is one of the main causes of the global decline in amphibians. The aetiological agent is ubiquitous, with worldwide distribution, and affects a large number of amphibian species in several biomes. In the last decade, scientific research has substantially increased knowledge of the aetiological agent and the associated infection. However, important epidemiological aspects of the environment-mediated interactions between the aetiological agent and the host are not yet clear. The objective of the present review is to describe chytridiomycosis with regard to the major features of the aetiological agent, the host and the environment.
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.