Infectious disease threats to amphibian conservation

The unexplained decline of amphibian populations across the world was first recognised in the late 20th century. When investigated, most of these “enigmatic” declines have been shown to be due to one of two types of infectious disease: ranavirosis caused by infection with FV3-like ranavirus or with common midwife toad virus, or chytridiomycosis caused by infection with Batrachochytrium dendrobatidis or B. salamandrivorans. In all cases examined, infection has been via the human-mediated introduction of the pathogen to a species or population in which it has not naturally co-evolved. While ranaviruses and B. salamandrivorans have caused regionally localised amphibian population declines in Europe, the chytrid fungus, B. dendrobatidis, has caused catastrophic multi-species amphibian population declines and species extinctions globally. These diseases have already caused the loss of amphibian biodiversity, and over 40% of known amphibian species are threatened with extinction. If this biodiversity loss is to be halted, it is imperative that regulations are put in place – and enforced – to prevent the spread of known and yet-to-be discovered amphibian pathogens. Also, it is incumbent on those who keep or study amphibians to take measures to minimise the risk of disease spread, including from captive animals to those in the wild.

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Composition of symbiotic bacteria predicts survival in Panamanian golden frogs infected with a lethal fungus

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2014.2881 ◽

2015 ◽

Vol 282 (1805) ◽

pp. 20142881 ◽

Cited By ~ 74

Author(s):

Matthew H. Becker ◽

Jenifer B. Walke ◽

Shawna Cikanek ◽

Anna E. Savage ◽

Nichole Mattheus ◽

...

Keyword(s):

Batrachochytrium Dendrobatidis ◽

Population Declines ◽

Amphibian Species ◽

Amphibian Population ◽

New Approach ◽

Skin Bacteria ◽

Probiotic Treatment ◽

Host Health ◽

The Face ◽

Inhibitory Bacteria

Symbiotic microbes can dramatically impact host health and fitness, and recent research in a diversity of systems suggests that different symbiont community structures may result in distinct outcomes for the host. In amphibians, some symbiotic skin bacteria produce metabolites that inhibit the growth of Batrachochytrium dendrobatidis (Bd), a cutaneous fungal pathogen that has caused many amphibian population declines and extinctions. Treatment with beneficial bacteria (probiotics) prevents Bd infection in some amphibian species and creates optimism for conservation of species that are highly susceptible to chytridiomycosis, the disease caused by Bd. In a laboratory experiment, we used Bd-inhibitory bacteria from Bd-tolerant Panamanian amphibians in a probiotic development trial with Panamanian golden frogs, Atelopus zeteki , a species currently surviving only in captive assurance colonies. Approximately 30% of infected golden frogs survived Bd exposure by either clearing infection or maintaining low Bd loads, but this was not associated with probiotic treatment. Survival was instead related to initial composition of the skin bacterial community and metabolites present on the skin. These results suggest a strong link between the structure of these symbiotic microbial communities and amphibian host health in the face of Bd exposure and also suggest a new approach for developing amphibian probiotics.

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Ancestral chytrid pathogen remains hypervirulent following its long coevolution with amphibian hosts

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2019.0833 ◽

2019 ◽

Vol 286 (1904) ◽

pp. 20190833 ◽

Cited By ~ 3

Author(s):

Minjie Fu ◽

Bruce Waldman

Keyword(s):

Batrachochytrium Dendrobatidis ◽

Population Declines ◽

Amphibian Species ◽

South Korean ◽

Global Pandemic ◽

Litoria Caerulea ◽

Experimental Treatments ◽

Amphibian Chytrid Fungus ◽

Genomic Recombination ◽

Blank Solution

Many amphibian species around the world, except in Asia, suffer morbidity and mortality when infected by the emerging infectious pathogen Batrachochytrium dendrobatidis (Bd). A lineage of the amphibian chytrid fungus isolated from South Korean amphibians (BdAsia-1) is evolutionarily basal to recombinant global pandemic lineages (BdGPL) associated with worldwide amphibian population declines. In Asia, the Bd pathogen and its amphibian hosts have coevolved over 100 years or more. Thus, resilience of Asian amphibian populations to infection might result from attenuated virulence of endemic Bd lineages, evolved immunity to the pathogen or both. We compared susceptibilities of an Australasian amphibian, Litoria caerulea , known to lack resistance to BdGPL, with those of three Korean species, Bufo gargarizans , Bombina orientalis and Hyla japonica , after inoculation with BdAsia-1, BdGPL or a blank solution. Subjects became infected in all experimental treatments but Korean species rapidly cleared themselves of infection, regardless of Bd lineage. They survived with no apparent secondary effects. By contrast, L. caerulea , after infection by either BdAsia-1 or BdGPL, suffered deteriorating body condition and carried progressively higher Bd loads over time. Subsequently, most subjects died. Comparing their effects on L. caerulea , BdAsia-1 induced more rapid disease progression than BdGPL. The results suggest that genomic recombination with other lineages was not necessary for the ancestral Bd lineage to evolve hypervirulence over its long period of coevolution with amphibian hosts. The pathogen's virulence may have driven strong selection for immune responses in endemic Asian amphibian host species.

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Body size mediates latitudinal population differences in response to Bd infection in two amphibian species.

10.1101/2021.07.16.452656 ◽

2021 ◽

Author(s):

Sara Meurling ◽

Maria Cortazar-Chinarro ◽

Mattias Siljestam ◽

David Ahlen ◽

Erik Agren ◽

...

Keyword(s):

Body Size ◽

Batrachochytrium Dendrobatidis ◽

Geographical Origin ◽

Bufo Bufo ◽

Northern Region ◽

Population Declines ◽

Rana Arvalis ◽

Amphibian Species ◽

Survival Difference ◽

Species Survival

Populations of the same species may differ in their sensitivity to pathogens but the factors behind this variation are poorly understood. Moreover, infections may cause sub-lethal fitness effects even in species resistant or tolerant to disease. The chytrid fungus Batrachochytrium dendrobatidis (Bd), is a generalist pathogen which has caused amphibian population declines worldwide. In many species, Bd infection causes the disease chytridiomycosis, often leading to high mortality. We investigated how geographical origin affects tolerance to Bd by exposing newly metamorphosed individuals of two North European amphibians (moor frog Rana arvalis, common toad Bufo bufo) from two latitudinal regions to two different BdGPL strains. Bd exposure strongly lowered survival in B. bufo, and in both species survival was lower in the northern region, this difference being much stronger in B. bufo. Northern individuals were smaller in both species, and the survival difference between the regions was size-mediated with smaller individuals being more sensitive to Bd. In both species, Bd exposure led to sub-lethal effects in terms of reduced growth suggesting that even individuals surviving the infection may have reduced fitness mediated by smaller body size. Bd strain affected size-dependent mortality differently in the two regions. We discuss the possible mechanisms how body size and geographical origin can contribute to the present results.

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Genetic characterization of chytrids isolated from larval amphibians collected in central and east Texas

10.1101/451385 ◽

2018 ◽

Author(s):

Thomas L. Marshall ◽

Carlos R. Baca ◽

Decio T. Correa ◽

Michael R. J. Forstner ◽

Dittmar Hahn ◽

...

Keyword(s):

Batrachochytrium Dendrobatidis ◽

Current Knowledge ◽

Western Hemisphere ◽

Coi Gene ◽

Population Declines ◽

East Texas ◽

Global Knowledge ◽

Amphibian Population ◽

South Central ◽

Central Texas

ABSTRACTChytridiomycosis, 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 not known to infect amphibians from east Texas. 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 Bd-GPL 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.

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Bioclimatic and anthropogenic variables shape the occurrence of Batrachochytrium dendrobatidis over a large latitudinal gradient

Scientific Reports ◽

10.1038/s41598-021-96535-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Mario Alvarado-Rybak ◽

Manuel Lepe-Lopez ◽

Alexandra Peñafiel-Ricaurte ◽

Andrés Valenzuela-Sánchez ◽

Catalina Valdivia ◽

...

Keyword(s):

Latitudinal Gradient ◽

Batrachochytrium Dendrobatidis ◽

Biodiversity Loss ◽

Quantitative Real Time Pcr ◽

Amphibian Skin ◽

Amphibian Species ◽

Risk Areas ◽

Host Ecology ◽

New Evidence ◽

Central South

AbstractAmphibian chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has caused the greatest known loss of biodiversity due to an infectious disease. We used Bd infection data from quantitative real-time PCR (qPCR) assays of amphibian skin swabs collected across Chile during 2008–2018 to model Bd occurrence with the aim to determine bioclimatic and anthropogenic variables associated with Bd infection. Also, we used Bd presence/absence records to identify geographical Bd high-risk areas and compare Bd prevalence and infection loads between amphibian families, ecoregions, and host ecology. Data comprised 4155 Bd-specific qPCR assays from 162 locations across a latitudinal gradient of 3700 km (18º to 51ºS). Results showed a significant clustering of Bd associated with urban centres and anthropogenically highly disturbed ecosystems in central-south Chile. Both Bd prevalence and Bd infection loads were higher in aquatic than terrestrial amphibian species. Our model indicated positive associations of Bd prevalence with altitude, temperature, precipitation and human-modified landscapes. Also, we found that macroscale drivers, such as land use change and climate, shape the occurrence of Bd at the landscape level. Our study provides with new evidence that can improve the effectiveness of strategies to mitigate biodiversity loss due to amphibian chytridiomycosis.

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The Effects of Habitat Modification on a Spotted Frog Population in Yellowstone National Park

The UW National Parks Service Research Station Annual Reports ◽

10.13001/uwnpsrc.1993.3129 ◽

1993 ◽

Vol 17 ◽

pp. 3-13

Author(s):

Debra Patla ◽

Charles Peterson

Keyword(s):

Landscape Connectivity ◽

Habitat Destruction ◽

Habitat Modification ◽

Population Declines ◽

Amphibian Species ◽

Amphibian Population ◽

Breeding Sites ◽

Population Responses ◽

Sustainable Resource Use

Declines and extinctions of many populations of amphibians have been noted worldwide in recent years (Corn and Fogelman 1984, Beiswenger 1986, McAllister and Leonard 1990, Wake and Morowitz 1990, Wake 1991, Adler 1992). Habitat modifications due to human activities may contribute to many of these declines. Habitat may be destroyed overtly, or it may be fragmented. Fragmentation results in reduced area, a differential loss of important habitat components, and increased isolation of populations (Wyman 1990). The persistence of amphibians in areas where modifications short of total habitat destruction occur depends on the preservation of essential habitat components and landscape connectivity that allows individual animals access to breeding, foraging, and wintering sites (Sinsch 1989). Long-term persistence also may rely on the immigration of individuals from other populations (Pechmann et al. 1991, Sjogren 1991). Our efforts to conserve amphibian species and to establish methods of sustainable resource use depend on our understanding of habitat fragmentation and knowledge of the behavioral and population responses to different types of habitat modifications (Gibbons 1988, Groom and Schumaker 1993). Few studies have addressed these types of questions. Notable exceptions include some studies on the effects of logging (Corn and Bury 1989) and acidification (Wyman and Hawksley-Lescault 1988, Harte and Hoffman 1989, Corn and Vertucci 1992). In Europe, researchers and wildlife conservationists are investigating the impacts of roads on amphibians and attempting to find solutions to fragmentation and mortality effects (Langton 1989), but this concern has not yet received noticeable attention in North America. We lack studies evaluating the relative importance and integration of foraging areas, hibernacula, breeding sites, areas occupied pre- and post-breeding, and dispersal routes connecting these areas. With these kinds of information, researchers and land managers will acquire the ability to better analyze, predict, and mitigate the effects of habitat modifications that are sources of amphibian population declines.

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Side effects of itraconazole on post-metamorphic Alytes obstetricans after a cold stress

Amphibia-Reptilia ◽

10.1163/15685381-00003064 ◽

2016 ◽

Vol 37 (4) ◽

pp. 345-357 ◽

Cited By ~ 2

Author(s):

Adeline Loyau ◽

Jérémie H. Cornuau ◽

Frances C. Clare ◽

Dirk S. Schmeller

Keyword(s):

Side Effects ◽

Cold Stress ◽

Batrachochytrium Dendrobatidis ◽

Cold Water ◽

Amphibian Declines ◽

Amphibian Species ◽

Proximate Cause ◽

In The Wild ◽

Itraconazole Treatment ◽

Alytes Obstetricans

Itraconazole is the most widely used treatment against Batrachochytrium dendrobatidis (Bd), the fungal pathogen causing chytridiomycosis, a proximate cause of amphibian declines. Several side effects of itraconazole treatment, ranging in severity from depigmentation to death have been reported in different amphibian species and life stages, and these side effects were observed at commonly used dosages of itraconazole. However, no studies have investigated side-effects of itraconazole in conjunction with environmental stress. Post-metamorphic midwife toads (Alytes obstetricans) that were treated with itraconazole and subsequently exposed to a cold stress (exposure to 4°C cold water) had higher mortality rates compared to untreated individuals. Moreover, adults of booroolong frogs (Litoria booroolongensis) treated with itraconazole had a higher probability to become infected when subsequently exposed to Bd. Our results suggest that a post-metamorphosis itraconazole treatment of infected midwife toads combined with a subsequent release into the wild may be an ineffective disease mitigation strategy, as the cold stress during hibernation and/or exposure to Bd in the wild may reduce the hibernation emergence rate of treated individuals in this species.

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Single infection with Batrachochytrium dendrobatidis or Ranavirus does not increase probability of co-infection in a montane community of amphibians

Scientific Reports ◽

10.1038/s41598-020-78196-3 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Jaime Bosch ◽

Camino Monsalve-Carcaño ◽

Stephen J. Price ◽

Jon Bielby

Keyword(s):

Batrachochytrium Dendrobatidis ◽

Disease Outbreaks ◽

Single Infection ◽

Chytrid Fungus ◽

Population Declines ◽

Emerging Pathogens ◽

Amphibian Species ◽

Management Interventions ◽

Amphibian Chytrid Fungus ◽

Common Situation

AbstractUnderstanding the occurrence and consequence of co-infections can be useful in designing disease management interventions. Amphibians are the most highly threatened vertebrates, and emerging pathogens are a serious threat to their conservation. The amphibian chytrid fungus and the viruses of the Ranavirus genus are already widely distributed, causing disease outbreaks and population declines worldwide. However, we lack information about the occurrence and consequences of coinfection with these pathogens across age-classes of amphibian hosts. Here, we analyze the occurrence of infection of the amphibian chytrid fungus and ranaviruses during one season in two susceptible amphibian species at two different locations at which outbreaks have occurred. We found that the co-occurrence of both pathogens in a particular host is not common except in highly susceptible life-stages, and that single infections are the most common situation. Moreover, we found that the occurrence of one pathogen in a particular host did not predict the occurrence of the other. We attribute these results to the niches in which both pathogens proliferate in amphibian hosts.

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Review: Examining the Natural Role of Amphibian Antimicrobial Peptide Magainin

Molecules ◽

10.3390/molecules25225436 ◽

2020 ◽

Vol 25 (22) ◽

pp. 5436

Author(s):

Katelyn A. M. McMillan ◽

Melanie R. Power Coombs

Keyword(s):

Immune System ◽

Batrachochytrium Dendrobatidis ◽

Conservation Strategy ◽

Population Declines ◽

Small Peptides ◽

Amphibian Species ◽

Host Defense Peptides ◽

African Clawed Frog ◽

The North ◽

Clawed Frog

Host defense peptides (HDPs) are a group of antimicrobial peptides (AMPs) that are crucial components of the innate immune system of many different organisms. These small peptides actively kill microbes and prevent infection. Despite the presence of AMPs in the amphibian immune system, populations of these organisms are in decline globally. Magainin is an AMP derived from the African clawed frog (Xenopus laevis) and has displayed potent antimicrobial effects against a wide variety of microbes. Included in this group of microbes are known pathogens of the African clawed frog and other amphibian species. Arguably, the most deleterious amphibious pathogen is Batrachochytrium dendrobatidis, a chytrid fungus. Investigating the mechanism of action of magainin can help understand how to effectively fight off infection. By understanding amphibian AMPs’ role in the frog, a potential conservation strategy can be developed for other species of amphibians that are susceptible to infections, such as the North American green frog (Rana clamitans). Considering that population declines of these organisms are occurring globally, this effort is crucial to protect not only these organisms but the ecosystems they inhabit as well.

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Endemic Infection of Batrachochytrium dendrobatidis in Costa Rica: Implications for Amphibian Conservation at Regional and Species Level

Diversity ◽

10.3390/d11080129 ◽

2019 ◽

Vol 11 (8) ◽

pp. 129 ◽

Cited By ~ 1

Author(s):

Héctor Zumbado-Ulate ◽

Kiersten N. Nelson ◽

Adrián García-Rodríguez ◽

Gerardo Chaves ◽

Erick Arias ◽

...

Keyword(s):

Costa Rica ◽

Batrachochytrium Dendrobatidis ◽

Infection Intensity ◽

Amphibian Conservation ◽

Conservation Strategies ◽

Amphibian Species ◽

Current Impact ◽

Taxonomic Groups ◽

Species Descriptions ◽

Effective Conservation

Batrachochytrium dendrobatidis (Bd) has been associated with the severe declines and extinctions of amphibians in Costa Rica that primarily occurred during the 1980s and 1990s. However, the current impact of Bd infection on amphibian species in Costa Rica is unknown. We aimed to update the list of amphibian species in Costa Rica and evaluate the prevalence and infection intensity of Bd infection across the country to aid in the development of effective conservation strategies for amphibians. We reviewed taxonomic lists and included new species descriptions and records for a total of 215 amphibian species in Costa Rica. We also sampled for Bd at nine localities from 2015–2018 and combined these data with additional Bd occurrence data from multiple studies conducted in amphibian communities across Costa Rica from 2005–2018. With this combined dataset, we found that Bd was common (overall infection rate of 23%) across regions and elevations, but infection intensity was below theoretical thresholds associated with mortality. Bd was also more prevalent in Caribbean lowlands and in terrestrial amphibians with an aquatic larval stage; meanwhile, infection load was the highest in direct-developing species (forest and stream-dwellers). Our findings can be used to prioritize regions and taxonomic groups for conservation strategies.

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