Fish and Wildlife Disease

Chytrid Fungus: Detection in Aquatic Environments (Kirshtein)

Chytrid Fungus: Occurrence in Southern California
(Wood, Backlin)

Chytrid Fungus: Presence and Effects in the Rocky Mountains
(Muths, Pilliod)

Rana luteventris at Two Medicine Pond, Glacier National Park. Photo credit: Collaborator Chauncey Anderson, USGS Image Gallery

Global amphibian declines are a huge concern, as amphibians are believed to be an indicator species of environmental health. There is also interest because understanding amphibian declines may be a model for assessing other species. The fungal pathogen Batrachochytrium dendrobatidis (Bd) causes chytridiomycosis, a disease implicated in amphibian declines on five continents. Bd attacks the pigmented mouthparts of infected tadpoles and is frequently lethal to postmetamorphic frogs. Despite the threats to amphibians posed by Bd and its widespread distribution, little is known about its life history, the circumstances under which it becomes infectious, or the mechanisms by which it spreads. Chytridiomycosis has been studied in laboratories but field investigations have been impeded by a lack of available detection methods, as Bd can be detected in infected animals but not in their environment. There exists a need for field studies addressing the distribution and transport, exposure mechanisms and transmission, infectivity, ecology, and life history of Bd. Polymerase chain reaction (PCR) primer sets exist with which amphibians can be tested for this disease and advances in sampling techniques allow non-invasive testing of animals. We recently developed filtering and PCR based quantitative methods by modifying existing PCR assays to detect Bd DNA in water and sediments without the need for testing amphibians. This technique will allow researchers to study the implications of Bd's presence in water bodies, to monitor water bodies before reintroduction efforts and to investigate the spread of Bd across the landscape.

For more information view the project summary Detection of Batrachochytrium dendrobatidis (Chytrid Fungus) in Aquatic Environments and the following publication:

Kirshtein J.D., Anderson C.W., Wood J.S., Longcore J.E., and Voytek M.A., 2007, Quantitative PCR detection of Batrachochytrium dendrobatidis DNA from sediments and water: Diseases of Aquatic Organisms v. 77 p.11-15.

Also contact Julie Kirshtein, Voytek Microbiology.

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An endangered Southern California frog, the Mountain Yellow-legged frog (Rana muscosa). Photo credit: Adam R. Backlin, USGS Image Gallery

Chytridiomycosis, an infectious skin disease caused by the chytrid fungus Batrachochytrium dendrobatidis (hereafter Bd), has been linked to population declines and mass mortalities of amphibians in many parts of the world, including Australia, Europe, Africa, and the Americas. Although the origins of the fungus remain unclear, the sudden appearance of genetically similar Bd strains across several continents (North America, Central America, and Australia) suggests the fungus has been recently introduced to many regions, and is rapidly spreading within them.

In North America, recent surveys have confirmed the occurrence of Bd in a number of amphibian species throughout the east and in the Pacific Northwest. However, much of what is known of the geographic distribution and prevalence of Bd in southern California comes from incidental detections rather than concerted systematic surveys of the region. Researchers at the USGS San Diego Field Station, in collaboration with the USGS Wildlife Heath Center and the Wildlife Disease Laboratories at the San Diego Zoo, have been sampling amphibian populations in diverse, and in some cases extremely remote habitats throughout southern California between 2000 and 2009 to provide a geographical and taxonomic overview of the current distribution of Bd in southern California. Obtaining this type of information is an important first step in assessing the threat that this pathogen may pose to amphibians in this region. In particular, several of our long-term surveys include federally threatened and endangered species, which may be at extreme risk of extinction (e.g. Mountain Yellow-legged frog, Rana muscosa; Red-legged frog, Rana draytonii; Arroyo toad, Anaxyrus californicus). This information will serve as a baseline for further research on the effects of Bd in southern California, including where and when the fungus was introduced, assessing epidemiological trends across time and space, ecological requirements for successful pathogen survival and transmission, and the identification of amphibian species that are susceptible to lethal infection outcomes.

For more information contact Dustin A. Wood, Western Ecological Research Center, and Adam R. Backlin, Western Ecological Research Center.

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R. Scherer searches for toads at Blackrock. Photo credit: Erin Muths, USGS

Amphibian populations worldwide continue to be imperiled by the amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd). This infectious disease is linked to extirpations and extinctions at sites from Australia to Spain and from Panama to Colorado. Where Bd occurs, how it may be limited by environmental factors, and how it affects the demographics of affected populations, are critical pieces to the puzzle of amphibian decline. The answers will shape our efforts to arrest decline and effectively conserve amphibians. In a two-pronged project, we have assessed the presence of Bd on a landscape scale and addressed the effects of the disease at a population level through capture-recapture work with Bufo boreas (boreal toads) at three sites in the Rocky Mountain west.

In part one, we assessed the presence of this pathogen along an eleven degree latitudinal gradient in the Rocky Mountains, a first regional-level, field-based effort to examine the relationship of environmental and geographic factors to the distribution of this fungus. We found that Bd is widespread in this area, but was found at a higher proportion of low versus high elevation breeding sites, suggesting that, at least in higher elevations in the temperate zone, the occurrence or persistence of Bd is limited by temperature which is, in turn, constrained by elevation. This sort of information can play a role in the selection of potential sites for future salvage operations or reintroductions of endangered amphibians.

Determining how population demographic parameters (i.e., survival, birth, death, emigration, and immigration) are influenced by this disease is one path to understanding the apparent variability among populations in susceptibility to Bd. Despite the abundance of recent research on Bd, there are few data that compare demographic parameters between infected and uninfected populations or that assess the effects of environmental covariates on survival. In part two, we assessed survival and population growth at three boreal toad populations, two where Bd is present and one where Bd has not been detected. We are currently using a priori hypothesis testing to provide a quantitative analysis of demographic differences between amphibian populations infected with Bd compared with uninfected populations.

For more information see the following publication:

Muths, E., D.S. Pilliod, and L.J. Livo. 2008. Distribution and environmental limitations of an amphibian pathogen in the Rocky Mountains, USA. Biological Conservation, 141:1484-1492.

Also contact Erin Muths, Fort Collins Science Center and David Pilliod, Forest and Rangeland Ecosystem Science Center.

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