title: Diagnostic methodology is critical for accurately determining the prevalence of Ichthyophonus infections in wild fish populations.
abstract: Several different techniques have been employed to detect and identify Ichthyophonus spp. in infected fish hosts; these include macroscopic observation, microscopic examination of tissue squashes, histological evaluation, in vitro culture, and molecular techniques. Examination of the peer-reviewed literature revealed that when more than 1 diagnostic method is used, they often result in significantly different results; for example, when in vitro culture was used to identify infected trout in an experimentally exposed population, 98.7% of infected trout were detected, but when standard histology was used to confirm known infected tissues from wild salmon, it detected ~50% of low-intensity infections and ~85% of high-intensity infections. Other studies on different species reported similar differences. When we examined a possible mechanism to explain the disparity between different diagnostic techniques, we observed non-random distribution of the parasite in 3-dimensionally visualized tissue sections from infected hosts, thus providing a possible explanation for the different sensitivities of commonly used diagnostic techniques. Based on experimental evidence and a review of the peer-reviewed literature, we have concluded that in vitro culture is currently the most accurate diagnostic technique for determining infection prevalence of Ichthyophonus , particularly when the exposure history of the population is not known.
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington 98195, USA. kocan@uw.edu
authors.forename: Richard
authors.initials: R
authors.lastname: Kocan
authors.forename: Heather
authors.initials: H
authors.lastname: Dolan
authors.forename: Paul
authors.initials: P
authors.lastname: Hershberger
mesh_terms: D000413:Alaska / Q000453:epidemiology; D000818:Animals; D000835:Animals, Wild; D005260:Female; D005393:Fish Diseases / Q000175:diagnosis* / Q000453:epidemiology / Q000469:parasitology; D005399:Fishes; D008297:Male; D050298:Mesomycetozoea / Q000302:isolation & purification*; D050738:Mesomycetozoea Infections / Q000175:diagnosis* / Q000453:epidemiology / Q000469:parasitology; D018482:Muscle, Skeletal / Q000469:parasitology; D017686:Oncorhynchus mykiss / Q000469:parasitology*; D015995:Prevalence; D045483:Rivers; D012474:Salmon / Q000469:parasitology*; D012867:Skin / Q000473:pathology; D014861:Washington / Q000453:epidemiology