title: Effect of Exposure Dose on Ichthyophonus Prevalence and Infection Intensity in Experimentally Infected Rainbow Trout, Oncorhynchus mykiss.
abstract: This study describes the effect of increasing exposure dose on Ichthyophonus prevalence and infection intensity in experimentally infected rainbow trout, Oncorhynchus mykiss. Specific-pathogen free trout were exposed per os to increasing numbers of Ichthyophonus schizonts obtained from naturally infected donor fish, then sampled after 30 and 60 days post-exposure. Both in vitro explant culture and histology revealed that as the number of schizonts per dose increased there was a proportionate increase in the number of infected fish, as well as an increase in the number of infected organs; parasite density in individual infected organs also increased with dose. Explant culture revealed that all fish exposed to the highest dose (≥2,080 schizonts) became infected, while only 67% of those exposed to the intermediate dose (1,040-1,153 schizonts) were Ichthyophonus-positive after 60 days; Ichthyophonus was not detected in fish exposed to the 2 lowest doses (≤280 schizonts). Histologic examination of individual infected organs also revealed increasing infection prevalence and parasite density in response to exposure to increasing numbers of Ichthyophonus schizonts.
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington 98195.
authors.forename: Richard
authors.initials: R
authors.lastname: Kocan
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington 98195.
authors.forename: Scott
authors.initials: S
authors.lastname: LaPatra
mesh_terms: D000818:Animals; D016782:Apicomplexa / Q000254:growth & development / Q000502:physiology*; D005260:Female; D005393:Fish Diseases / Q000453:epidemiology* / Q000469:parasitology; D006321:Heart / Q000469:parasitology; D007668:Kidney / Q000469:parasitology / Q000473:pathology; D008099:Liver / Q000469:parasitology / Q000473:pathology; D009132:Muscles / Q000469:parasitology / Q000473:pathology; D009206:Myocardium / Q000473:pathology; D017686:Oncorhynchus mykiss / Q000469:parasitology*; D015995:Prevalence; D011529:Protozoan Infections, Animal / Q000453:epidemiology* / Q000469:parasitology; D052939:Schizonts / Q000254:growth & development / Q000502:physiology; D013047:Specific Pathogen-Free Organisms