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Patuxent Wildlife Research Center

Amphibian Disease List

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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. 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. In 2001, ranavirus outbreaks were documented in spotted salamanders, green frogs, wood frogs, spring peepers and bullfrogs at Acadia and Patuxent. In recent years, Ranavirus outbreaks have caused amphibian die-offs in Maine, Massachusetts, New Hampshire, and Rhode Island.

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Ichthyophonus fungus
The ichthyophonus fungus is principally a disease agent of fish, and is known to cause massive fish kills in fresh water and marine fish. In 2001, we found an adult male wood frog at Patuxent which was extremely emaciated and listless. The wood frog died of a massive infection of the skeletal muscles (mycotic myositis) with the ichthyophonus fungus. Icthyophonus fungal infections have been noted occasionally in late stage tadpoles and recent metamorphs, but rarely in adult anurans. However, red-spotted newts severely infected with the fungus have been reported from West Virginia and Vermont.

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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. While other ARMI regions have documented amphibian chytridiomycosis (see detailed information on RARMI web site), no amphibians we have sent to the National Wildlife Health Center (NWHC, Dr. David Green) have been diagnosed with chytrid infections. NE ARMI will specifically look for chytrid infections in 2002 at Apex Sites. Dr. Jerry Longcore and Laura Eton-Poole have reported chytrid fungus in amphibians at various Refuges and other areas in the Northeast.

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Water Mold (Saprolegniasis)
In 2001, water molds were detected in spotted salamander egg masses in Acadia. Only a few cases of Saprolegniasis have been clinically documented in amphibians in the Northeast. Water molds (i.e., Saprolegniasis) were detected in two of two Ambystoma maculatum egg masses from two sites in Acadia National Park, Maine, but it could not be determined if the eggs were alive or dead at the time the fungi invaded them (Dr. David E. Green, pers.comm.).

The Saprolegniasis fungus Saprolegnia ferax has been associated with embryonic die-offs of amphibian populations in the Cascade Mountains of Oregon, U.S.A. Saprolegniasis is a common disease found in fish, especially those reared in hatcheries (Richards and Pickering 1978 as cited in Kiesecker et al. 2001b). Many fish stocked in lakes of North America’s Pacific Northwest are common carriers of Saprolegnia, including S. ferax (Wood and Willoughby 1986). Kiesecker et al. (2001b) performed laboratory experiments in which they examined whether rainbow trout (Oncorhyncus mykiss) can act as a vector for transferring S. ferax to populations of boreal toads (Bufo boreas). They experimentally infected rainbow trout with S. ferax and found that mortality was significantly greater in boreal toad embryos exposed to infected trout when compared to control embryos. Boreal toad embryos raised on soil exposed to infected rainbow trout also developed significant S. ferax infections. Interestingly, those embryos exposed to S. ferax collected from areas where Saprolegnia infections were common experienced higher mortality rates than embryos exposed to S. ferax collected from areas where Saprolegnia outbreaks had not occurred (Kiesecker et al. 2001b). Kiesecker at al. (2001a) propose another method by which Saprolegnia may be impacting montane amphibian populations. In their study, they found 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.

Kiesecker, J. M., A. R. Blaustein, and L. K. Belden. 2001a. Complex causes of amphibian population declines. Nature 410:681-684.

Kiesecker, J. M., A. R. Blaustein, and C. L. Miller. 2001b. Transfer of a pathogen from fish to amphibians. Conservation Biology 15:1064-1070.

Richards, R. H., and A. D. Pickering. 1978. Frequency and distribution patterns of Saprolegia infection in wild and hatchery-reared brown trout Salmo trutta and char Salvelinus alpinus. Journal of Fish Diseases 1:69-82.

Wood, S. E., and L. G. Willoughby. 1986. Ecological observations on the fungal colonization of fish by Saprolegniaceae in Windermere. Journal of Applied Ecology 23:737-740.

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Mesomycetozoan (yeast-like) organism
In 2001, a mesomycetozoan organism caused a die-off of wood frog tadpoles in Virginia.

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