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David K. Skelly
Yale University
School of Forestry & Environmental Studies
370 Prospect Street
New Haven, CT 06511 USA

Yale FES



Ecology of Disease

The ecology of infectious disease is poorly understood.  Parasites and pathogens are undoubtedly more ubiquitous and more important to ecological patterns than is currently appreciated.  Our laboratory has focused on two lines of disease related research.  In the first, we are working to understand how human development of landscapes affects the rates and consequences of infection by macroparasites.  Most of this work has focused on echinostomes, a trematode parasite with a complex life cycle that encysts in the kidneys of amphibians, appears to emerge in developed contexts and is associated with high rates of mortality in a field experiment.  

One related goal in this line of research is to develop new tools that can be used to diagnose infection noninvasively in preserved and live organisms.  A grant from the National Science Foundation is allowing us to develop the use of high resolution ultrasound technology to this end [abstract]. A preliminary goal is to use ultrasound to evaluate historical infection patterns captured in museum specimens.  We hope to contribute understanding to longstanding questions about the role of human development in the frequency and intensity of infection and disease.

A second line of disease research is focused on limb deformities in amphibians.  The leading suspected cause of deformities involves infection by Ribeiroia ondatrae, a trematode.  Exhaustive sampling in Vermont has failed to turn up any evidence of Ribeiroia demonstrating that high frequencies of deformities can occur over a large area in the absence of infection by Ribeiroia ondatrae.  These findings leave open the issue of what is causing deformities in Vermont and other regions where Ribeiroia is absent.  One possibility, exposure to chemical pollutants, is supported by an association between the risk of deformities and the proximity to agricultural sites.  Continuing work in collaboration with Gunter Wagner's group in Yale's Ecology & Evolutionary Biology Department will focus on identifying potential chemical agents of deformities and evaluating the mechanisms by which they cause abnormal development.

High resolution ultrasound image of tree frog (Hyla versicolor)
metamorph, showing echinostome cysts as bright white spots within kidney.


Leopard frog (Rana pipiens) larva; pre (left) and post (right) infection with echinostome cercaria.

Holland, M. P., D. K. Skelly, M. Kashgarian, S. R. Bolden, L. M. Harrison, M. Cappello. 2007. Echinostome infection in green frogs is stage and age dependent. Journal of Zoology 271:455-462.  Link

Skelly, D. K., S. R. Bolden, M. P. Holland, L. K. Freidenburg, N. A. Freidenfelds, and T. R. Malcolm. 2006. Urbanization and disease in amphibians. Pages 153-167 in S. Collinge and C. Ray (Eds.) Ecology of disease: community context and pathogen dynamics. Oxford University Press. ISBN 0198567081.

Skelly, D. K., S. R. Bolden, L. K. Freidenburg, N. A. Freidenfelds, and R. Levey.  2007. Ribeiroia infection is not responsible for Vermont Amphibian Deformities. EcoHealth 4:156-163.  Link

Taylor, B.,  Skelly, D. K., Demarchis, L. K., Slade, M. D., Rabinowitz, P. M. 2005. Proximity to pollution sources and risk of amphibian limb deformity. Environmental Health Perspectives 113:1497-1501.  Link

Deformed leopard frog (Rana pipiens) metamorph found near Lake Champlain in Vermont.