Emergence Of Chytridiomycosis Research Articles

Serratia marcescens shapes cutaneous bacterial communities and influences survival of an amphibian host.

Ongoing investigations into the interactions between microbial communities and their associated hosts are changing how emerging diseases are perceived and ameliorated. Of the numerous host-microbiome-disease systems of study, the emergence of chytridiomycosis (caused by Batrachochytrium dendrobatidis, hereafter Bd) has been implicated in ongoing declines and extinction events of amphibians worldwide. Interestingly, there has been differential survival among amphibians in resisting Bd infection and subsequent disease. One factor thought to contribute to this resistance is the host-associated cutaneous microbiota. This has raised the possibility of using genetically modified probiotics to restructure the host-associated microbiota for desired anti-fungal outcomes. Here, we use a previously described strain of Serratia marcescens (Sm) for the manipulation of amphibian cutaneous microbiota. Sm was genetically altered to have a dysfunctional pathway for the production of the extracellular metabolite prodigiosin. This genetically altered strain (Δpig) and the functional prodigiosin producing strain (wild-type, WT) were compared for their microbial community and anti-Bd effects both in vitro and in vivo. In vitro, Bd growth was significantly repressed in the presence of prodigiosin. In vivo, the inoculation of both Sm strains was shown to significantly influence amphibian microbiota diversity with the Δpig-Sm treatment showing increasing alpha diversity, and the WT-Sm having no temporal effect on diversity. Differences were also seen in host mortality with Δpig-Sm treatments exhibiting significantly decreased survival probability when compared with WT-Sm in the presence of Bd. These results are an important proof-of-concept for linking the use of genetically modified probiotic bacteria to host microbial community structure and disease outcomes, which in the future may provide a way to ameliorate disease and address critical frontiers in disease and microbial ecology.

An assessment of funding and publication rates in Herpetology

Currently, herpetofauna worldwide is facing enormous threats; the number of threatened species is increasing at an alarming rate and many species have gone extinct. Despite efforts of institutions and researchers to understand and address the causes of declines and raise awareness of herpetofauna conservation, there has been no systematic study to evaluate the allocation of funding for basic and applied research relevant to conservation, relative publication rates, and the relationship of these measures to a degree of threat among herpetological groups. This study addresses this gap and identifies strengths and weaknesses of herpetological research and conservation over the last 10 years (2008-2018). Frogs had the highest grant-publication index (1384), followed by lizards (695), turtles (678), snakes (461.5), salamanders (366.5), crocodiles (164), caecilians (25.5), worm lizards (23) and tuatara (10). Nonetheless, when the grant-publication index is divided by the number of threatened and data-deficient species within each group, it demonstrates that, proportionally and in ascending order, salamanders, snakes, lizards, worm lizards, frogs and caecilians are in most need of knowledge and on-going funding for their conservation and survival. I was able to document a continued shift in attention in herpetological research owing to the emergence of chytridiomycosis and the global decline of amphibians. Despite some caveats, these findings should represent a proxy for the allocation of research and conservation effort on herpetofauna worldwide. I suggest priorities for research and how to better direct efforts to herpetofauna conservation.

Population dynamics of the critically endangered toad Atelopus cruciger and the fungal disease chytridiomycosis.

Harlequin toads (Atelopus) are among the most severely impacted amphibians by the emergence of chytridiomycosis, a fungal disease caused by the pathogen Batrachochytrium dendrobatidis (Bd). Many species disappeared while others suffered drastic contractions of their geographic distribution to lower altitudes. A diminished virulence of Bd in warm habitats was proposed to explain the survival of lowland populations of harlequin toads (i.e. thermal refuge hypothesis). To understand the mechanisms that allow some populations to reach an endemic equilibrium with this pathogen, we estimated demographic and epidemiological parameters at one remnant population of Atelopus cruciger in Venezuela using mark-recapture data from 2007–2013. We demonstrated that Bd is highly virulent for A. cruciger, increasing the odds of dying of infected adults four times in relation to uninfected ones and reducing the life expectancy of reproductive toads to a few weeks. Despite an estimated annual loss of 18% of the reproductive population due to Bd-induced mortality, this population has persisted in an endemic equilibrium for the last decade through the large recruitment of healthy adults every year. Given the high vulnerability of harlequin toads to Bd in lowland populations, thermal refuges need to be redefined as habitats of reduced transmission rather than attenuated virulence.

Dynamics and genetics of a disease-driven species decline to near extinction: lessons for conservation.

Amphibian chytridiomycosis has caused precipitous declines in hundreds of species worldwide. By tracking mountain chicken (Leptodactylus fallax) populations before, during and after the emergence of chytridiomycosis, we quantified the real-time species level impacts of this disease. We report a range-wide species decline amongst the fastest ever recorded, with a loss of over 85% of the population in fewer than 18 months on Dominica and near extinction on Montserrat. Genetic diversity declined in the wild, but emergency measures to establish a captive assurance population captured a representative sample of genetic diversity from Montserrat. If the Convention on Biological Diversity’s targets are to be met, it is important to evaluate the reasons why they appear consistently unattainable. The emergence of chytridiomycosis in the mountain chicken was predictable, but the decline could not be prevented. There is an urgent need to build mitigation capacity where amphibians are at risk from chytridiomycosis.

Interventions for reducing extinction risk in chytridiomycosis-threatened amphibians.

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.

Silent Springs: Why Are All the Frogs “Croaking”?

Silent Springs: Why Are All the Frogs “Croaking”?

Infectious disease and amphibian population declines

Abstract.A series of recent papers have implicated pathogens and parasites in amphibian population declines. Here, we review evidence on the link between infectious disease and amphibian population declines. We conclude that available data provide the clearest link for the fungal disease amphibian chytridiomycosis, although other pathogens are also implicated. We suggest additional experimental and observational data that need to be collected to provide further support that these other pathogens are associated with declines. We suggest that, in common with many emerging infectious diseases (EIDs) of humans, domestic animals and other wildlife species, emergence of chytridiomycosis may be driven by anthropogenic introduction (pathogen pollution). Finally, we review a number of recent advances in the host–parasite ecology of chytridiomycosis that help explain its emergence and impact.