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Trematodes (Ribeiroia) NICHOLAS GLADSTONE, CHEYENNE MULLINS, CHRISTIAN PEAKE

What are Trematodes?

u  Class within the Phylum Platyhelminthes (flatworms) u  18,000-28,000 trematode species

u  Digenetic Trematodes (subclass Digenea) represent majority of diversity – Our Focus

u  Obligate parasites of molluscs and vertebrates

u  Characterized by a dorso-ventrally flattened body and by the presence of both an oral and ventral ‘sucker’

Trematode Life Cycle

u  Life cycles often involve two or more intermediate hosts in addition to a definitive host

u  All trematodes have a molluscan intermediate host (usually a gastropod)

u  Other secondary hosts include:

u  Amphibians

u  Fish

u  Insects

u  The definitive host is generally a vertebrate

u  Adult trematodes then reside in the digestive tract of the definitive host

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Habitat and Host-Parasite Interactions

u  Ribeiroia is specific to snails within the family Planorbidae for their first intermediate host

u  Distributed throughout North and South America

u  Occur in lentic or still water habitats

u  Average prevalence of 5% within snail populations

u  Post-snail parasitization, the metacercariae transition around the base of the hind limbs, cloaca, and o a lesser extent within the posterior coelom of an amphibian host.

Distribution of Ribeiroia

Why do We Care?

u  Malformed amphibians have increased over the last 30 years in several parts of North America

u  Recently, infection has been a widespread cause of limb malformations in both anurans and caudates

u  In laboratory infections, Ribeiroia parasites target the developing limb tissue of anuran larvae, inducing high rates of limb malformations similar to those in field reports

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How do Trematodes Lead to Increased Amphibian Mortality?

u  Consequences of Ribeiroia infection include:

u  Extra limbs

u  Missing limbs

u  Skin Webbings

u  In response to Ribeiroia exposure, multiple species have been shown to exhibit reduced survivorship

u  Western Toads

u  Northern Leopard Frogs

u  Pacific Treefrogs

Deformed Frog Parasite Life Cycle

         

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References

u  Blaustein, Andrew R., Barbara A. Han, Rick A. Relyea, Pieter TJ Johnson, Julia C. Buck, Stephanie S. Gervasi, and Lee B. Kats. "The complexity of amphibian population declines: understanding the role of cofactors in driving amphibian losses." Annals of the New York Academy of Sciences 1223, no. 1 (2011): 108-119.

u  Bowerman, Jay, Pieter TJ Johnson, and Tracy Bowerman. "Sublethal predators and their injured prey: linking aquatic predators and severe limb abnormalities in amphibians." Ecology 91, no. 1 (2010): 242-251.

u  Collins, James P. "Amphibian decline and extinction: what we know and what we need to learn." Diseases of aquatic organisms 92, no. 2-3 (2010): 93-99.

u  Johnson, Pieter TJ, Kevin B. Lunde, Euan G. Ritchie, and Alan E. Launer. "The effect of trematode infection on amphibian limb development and survivorship." Science 284, no. 5415 (1999): 802-804.

u  Johnson, Pieter TJ, Daniel R. Sutherland, J. M. Kinsella, and Kevin B. Lunde. "Review of the trematode genus Ribeiroia (Psilostomidae): ecology, life history and pathogenesis with special emphasis on the amphibian malformation problem." Advances in parasitology 57 (2004): 191-253.

u  Johnson, P. T. J., and Lunde, K. B. 2005. Parasite infection and limb malformations: a growing problem in amphibian conservation. In: Lannoo, M. J., ed., Amphibian Declines: The Conservation Status of United States Species, pp. 124–138. California: University of California Press.

u  Rohr, J. R., T. R. Raffel, and Stanley K. Sessions. "Digenetic trematodes and their relationship to amphibian declines and deformities." Amphibian biology 8 (2009): 3067-3088.

u  Rohr, Jason R., Anna M. Schotthoefer, Thomas R. Raffel, Hunter J. Carrick, Neal Halstead, Jason T. Hoverman, Catherine M. Johnson et al. "Agrochemicals increase trematode infections in a declining amphibian species." Nature 455, no. 7217 (2008): 1235-1239.

u  Rohr, Jason R., Thomas R. Raffel, Stanley K. Sessions, and Peter J. Hudson. "Understanding the net effects of pesticides on amphibian trematode infections." Ecological Applications 18, no. 7 (2008): 1743-1753.

u  http://www.science-art.com/gallery/52/52_9222008161747.jpg

u  http://fwgna.org/species/planorbidae/H_anceps2.jpg