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Diseases of Aquatic Organisms

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DAO 134:137-146 (2019)  -  DOI: https://doi.org/10.3354/dao03365

Comparison of direct and indirect techniques for evaluating endoparasite infections in wild-caught newts (Taricha torosa and T. granulosa)

Tawni B. Riepe, Dana M. Calhoun, Pieter T. J. Johnson*

Department of Ecology and Evolutionary Biology, University of Colorado, Ramaley N122 CB334, Boulder, CO 80309, USA
*Corresponding author:

ABSTRACT: Studies of amphibian parasites have increased over the past 20 yr, in part because of their role in amphibian population declines and deformities. Such patterns underscore the importance of non-lethal methods for detecting and quantifying endoparasitic infections. The goal of this study was to compare results of indirect methods (fecal smears and fecal floats) with quantitative necropsies to detect endoparasitic infections in adult newts. In 2015, we collected fecal samples from 68 adult newts (Taricha granulosa and T. torosa) in the East Bay region of California and used fecal smears, sodium nitrate fecal flotation solution, and Sheather’s sugar flotation solution to assess infection (i.e. the presence and/or abundance of a parasite). Across all methods, we detected 3 protozoans (Eimeria tarichae, Tritrichomonas sp., and Balantidium sp.) and 3 nematodes (Rhabdias tarichae, Cosmocercoides variabilis, and Chabaudgolvania sp.). Based on generalized linear mixed models, the likelihood of detection varied between hosts (with T. torosa showing more overall infection relative to T. granulosa) and by assessment method: while fecal smears were more sensitive in detecting protozoans, comprehensive necropsies were the most reliable for quantifying infections of R. tarichae. Nonetheless, both the likelihood of R. tarichae detection within fecal samples as well as the number of infectious stages observed correlated strongly with infection intensity from necropsy, highlighting the utility of non-lethal assessment methods. The overall congruence between indirect methods and gross necropsy helps to validate the use of less-invasive methods for parasite detection and abundance, especially for sensitive or protected host taxa such as amphibians.


KEY WORDS: Nematode · Protozoan · Amphibian decline · Parasite · Conservation · Disease ecology · Veterinary parasitology


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Cite this article as: Riepe TB, Calhoun DM, Johnson PTJ (2019) Comparison of direct and indirect techniques for evaluating endoparasite infections in wild-caught newts (Taricha torosa and T. granulosa). Dis Aquat Org 134:137-146. https://doi.org/10.3354/dao03365

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