ARMI > Amphibian Disease

Amphibian Disease

Disease is emerging as an important concern in the study of amphibian decline. While research at Northern Rocky Mountain Science Center (NRMSC) and Fort Collins Science Center (FORT) does not focus entirely on amphibian disease, the issue plays an important role in our activities.

Rocky Mountain Region ARMI Projects Relating to Amphibian Disease:

We suspect that amphibian chytridiomycosis is affecting populations of boreal toads in Rocky Mountain National Park (Rocky Mountain National Park). Chytrid fungus has been identified in the park and some populations are exhibiting the same characteristics of large amphibian die-offs noted in Panama and Australia in 1998. We believe that chytrid fungus is the proximate cause of the recent decline of boreal toads in Rocky Mountain National Park.

In collaboration with National Wildlife Health Center (NWHC, Dr. David Green) and Rocky Mountain National Park, we are conducting an evaluation of amphibian health in and around Rocky Mountain National Park. This new study will provide baseline data on amphibian health including incidence of chytrid and other fungal infections, the presence of viral infections, and overall health of amphibians.

Amphibian health evaluation includes taking blood samples and oral swabs from boreal toads (endangered in the State of Colorado), collecting representative live specimens of other amphibian species and the opportunistic collection of dead animals. The adult animals in these photographs were unharmed. Photographs courtesy of T. Barnes.

Chytrid fungus was found on dying boreal toads at the National Elk Refuge, Wyoming, in 2000, increasing our concern that the disease may be or may become widespread in the Rocky Mountains. Infected animals were also found in 2003.

National Elk Refuge, Jackson, Wyoming. Chytrid fungus was identified here on boreal toads in 2000. Photo: D. Patla.

National Elk Refuge, Jackson, Wyoming. Chytrid fungus was identified here on boreal toads in 2000. Photograph courtesy of D. Patla.

Amphibian chytridiomycosis:

Amphibian chytridiomycosis is the infection of amphibian skin cells by the microscopic fungus (Batrachochytrium dendrobatidis).

	Batrachochytrium dendrobatidis. Two jar-shaped zoosporangium, or thalli (A), and zoospores inside are clearly visible. The discharge tubule is also visible where the flagellated zoospores are released from the thallus (B). Photograph courtesy of A. Pessier, University of Illinois Zoological Pathology Program, Loyola University Medical Center.

Chytrid fungus has been identified in a number of states from Maine to North Dakota to California. In general, chytrids are a group of fungi that are found ubiquitously in soil, water, and even in the rumens of cows. This particular chytrid, however, seems to be specific to amphibians. It has been documented in various frogs, toads, and salamanders both in captivity and in the wild. Infection by this fungus causes thickening of the skin, and infected toads and frogs tend to shed skin frequently. Infection can be lethal in some amphibian species, including boreal toads, but the mode of death is unknown. The thickening of the skin may impair gas exchange and affect the animal's ability to absorb water. An alternate hypothesis is that the fungus may produce a toxin.

There are other amphibian diseases as well. Ranaviruses belong to the Iridovirus family and infect insects, fish, and amphibians. This type of virus is not known to infect persons or other warm-blooded animals. In the western United States, most die-offs attributed to ranaviruses have occurred in tiger salamanders, although recent testing has detected the virus in Columbia spotted frogs in Montana and mountain yellow-legged frogs in California. Hundreds or thousands of sick and dead amphibians can be found at affected sites. Usually, the virus infection occurs in larvae (tadpoles and aquatic salamanders with gills) and frogs that have just completed metamorphosis. Sick and recently dead amphibians show small ulcers in the skin and extensive reddening of the skin along the ventrum (stomach) and base of the limbs. Internally, the virus affects and destroys many organs, including blood vessels, skin, stomach, liver, kidneys, and spleen. Studies are under way to determine where the virus originates each year and whether the ranaviruses of frogs and salamanders are different. So far, ranaviruses have not been detected in toads, but have caused disease outbreaks in true frogs and tiger salamanders. As of February 2002, die-offs of amphibians due to ranavirus have occurred in 15 states, including California, Arizona, Utah, Idaho, Montana, North Dakota, Wyoming and Colorado.

What we are doing about amphibian disease:

As we learn more about chytrid fungus and other amphibian diseases, concern has grown that field scientists may be vectors for transmitting disease among study sites. We follow standard protocols developed by the Declining Amphibian Populations Task Force (DAPTF) to reduce the risk of carrying disease accidentally between habitats. These protocols should be used by anyone conducting fieldwork in and around amphibian habitat including wetlands, breeding sites, or upland areas known to be used by amphibians. In general, these protocols recommend disinfection of all equipment, including, but not limited to, waders, nets, and calipers in a > 10% bleach solution between drainages. Chytrid fungus spreads through waterborne zoospores. These spores, and the fungal thalli in which they are formed, can remain viable in mud or any damp place. For example, zoospores have been found in mud caked into the tread of a wader. Thorough scrubbing with a bleach solution is critical for proper disinfection of equipment. We disinfect equipment between all drainages and sometimes between discrete sites.

This link goes to a powerpoint presentation produced by Lauren Livo, Ph.D. and the Colorado Division of Wildlife. This presentation is a tool to provide information for field technicians working with amphibians.

In addition to following the protocols suggested by the DAPTF and the linked presentation, we are especially alert for apparent mass mortality or die-off events. We collect amphibians that are found dead and submit them to USGS-NWHC for pathological examination. We encourage partners and collaborators, and the general public, to report such events to NWHC or their local wildlife department.

Amphibian Disease

Rocky Mountain Region ARMI Projects Relating to Amphibian Disease:

National Elk Refuge, Jackson, Wyoming. Chytrid fungus was identified here on boreal toads in 2000. Photograph courtesy of D. Patla.

Amphibian chytridiomycosis:

What we are doing about amphibian disease:

Related Information

Amphibian Diseases Homepage

Partners in Reptile and Amphibian Conservation

Environmental Effects of Ozone Depletion

Host-pathogen Biology and the Global Decline of Amphibians

National Wildlife Health Center

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