Amphibian Diseases

Amphibian diseases are an important concern in the study of amphibian declines worldwide.  There are several diseases implicated in amphibian declines, including ranaviruses, chytrid fungus (Batrachochytrium dendrobatidis) and white fungus (Saprolegnia ferax), bacterial infections, and trematodes.  In some instances, diseases alone may not be a concern, but in combination with other environmental stressors they can be lethal to already weakened individuals.

ARMI researchers enter amphibian disease data into the ARMI database and send diseased or recently dead amphibians to the USGS National Wildlife Health Center in Madison, WI, where Dr. David E. Green examines and diagnoses the amphibians. As we learn more about amphibian diseases, concern has grown that field scientists may be vectors for transmitting diseases among study sites. We follow biosecurity protocols 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. Thorough scrubbing with a bleach solution is critical for proper disinfection of equipment.

Ranaviruses

Ranaviruses belong to the Iridovirus family and infect reptiles, fish, and amphibians. This type of virus is not known to infect persons or other warm-blooded animals. 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. Ranavirus outbreaks in the Northeast have led to more intensive study in recent years, and NEARMI is collaborating with researchers throughout the region to monitor the effects of this disease on amphibian populations (see Research and Monitoring section on Disease).

Chytrid fungus

Amphibian chytridiomycosis is the infection of amphibian skin cells by the microscopic fungus (Batrachochytrium dendrobatidis).  Chytrid fungus has been identified in a number of states from Maine to North Dakota to California, and can affect not only frogs and toads but also aquatic and terrestrial salamanders.  Adult amphibians infected with chytrid exhibit symptoms such as skin abnormalities, extended back legs, lethargy, and loss of righting reflex.  In larvae, jaw sheaths and tooth rows of tadpoles lack pigment or appear deformed, which may impede feeding activity.  Overall, it appears that chytrid infection disrupts the ability of amphibians to maintain fluid and electrolyte balance, impacting proper muscle and nerve function. 
Although the bacteria has been detected in the Northeast in a variety of habitats and species, it does not appear to be an immediate concern and we have documented no instances mass mortality due to chytrid infection.

Water molds (Saprolegniasis)

The Saprolegniasis fungus Saprolegnia ferax is a common fungus found in fish, especially those reared in hatcheries.  Many fish stocked in lakes of North America’s Pacific Northwest are common carriers of Saprolegnia, including S. ferax. Some research has suggested that reduction in water depth due to global climate change (specifically El Niño/Southern Oscillation cycles warming the Pacific and altering precipitation levels) is causing greater exposure of embryos to harmful UV-B radiation, making them more susceptible to Saprolegnia infections.

What you can do

We encourage partners and the general public to report amphibian disease outbreaks or mortality events to NWHC or their local wildlife department. We also encourage all amphibian surveyors to practice sterile techniques to help protect local amphibian populations.

Related Information

National Wildlife Health Center

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