"Salmon Poisoning" Disease. II. Second Intermediate Host Susceptibility Studies

Abstract

The fishes Cottus perplexus, Lampetra richardsoni, L. tridentata, and Richardsonius balteatus and the Pacific giant salmander, Dicamptodon ensatus, all from western Oregon streams, were found naturally infected with metacercariae of Nanophyetus salmincola, the salmon poisoning fluke. This is the first report of natural infections in an animal other than a fish and in nonsalmonid fishes. Fourteen species of fishes were experimentally infected: Salmo gairdneri, S. salar, S. trutta, Salvelinus fontinalis, S. namaycush, Lampetra richardsoni, Cottus perplexus, Carassius auratus, Richardsonius balteatus, Catostomus macrocheilus, Lepomis macrochirus, Gasterosteus a. aculeatus, G. a. microcephalus, and Gambusia affinis. This extends the number of salmonid and nonsalmonid fishes susceptible to experimental infection. Cysts from all five of the naturally infected animals and from 12 of the 14 experimentally infected fishes were given to hamsters by stomach tube. In all instances except one (probably because of low dosage), the identification of the parasites as N. salmincola was confirmed by recovery of adult flukes from the hamsters. The possibility that N. schikhobalowi from Far Eastern Siberian humans, dogs, cats, and foxes, Vulpes vulpes, and N. salmincola are synonymous is discussed. Nanophyetus salmincola, the salmon poisoning fluke, requires three hosts for the completion of its life cycle. The first intermediate host is Oxytrema silicula, a stream snail found only in Oregon west of the Cascade Mountains, north to the Olympic Peninsula in Washington, and in northern California. The second intermediate hosts are fishes in which the cercariae encyst. The definitive hosts are fish-eating mammals such as canids, raccoons, mink, lynx, and the skunk. The fluke is a vector for Neorickettsia helminthoeca, the etiologic agent of salmon poisoning disease, a usually fatal illness of canids. Salmon poisoning disease was reviewed by Philip (1955), and the life cycle of the parasite was studied by Bennington and Pratt (1960). On the basis of the initial work of Donham et al. (1926) and Simms et al. (1931a, b), and in the absence of reports to the contrary, it has long been believed that salmonids were the only species of fish capable of serving as Received for publication 19 August 1965. *This investigation was supported by Public Health Service Research Grant 1-ROI-AI0659901, from the NIAID. Technical Paper No. 2030, Oregon Agricultural Experiment Station. A contribution from the Pacific Cooperative Water Pollution and Fisheries Research Laboratories. This study is a part of a thesis submitted by the senior author to the Graduate School of Oregon State University in partial fulfillment of the requirements for the degree of Master of Science. second intermediate hosts for N. salmincola. Donham et al. (1926) did not find this parasite in the following nonsalmonid fishes (scientific names were not given) taken in western Oregon: two whitefish, two smelt, one chub, one sea bass, one silver perch, and five suckers. Simms et al. (1931b) were unable to find the parasite in the following nonsalmonid fishes (numbers examined not given) from western Oregon streams: Micropterus dolomieui, smallmouth bass; Thaleichthys pacificus, eulachon or Columbia River smelt; Catostomus macrocheilus, large-scale sucker; Mylocheilus caurinu , peamouth; and Acipenser transmontanus, white sturgeon. Pernot (1911) examined one mudcat (scientific name not given) and found it uninfected. The only attempts to experimentally infect nonsalmonid fishes with N. salmincola were those of Bennington and Pratt (1960). By placing fish and infected snails together in aquaria, they infected two speckled dace, Rhinichthys osculus, one riffle sculpin, Cottus gulosus (probably perplexus in view of present knowledge of the distribution of these fishes in Oregon), and two goldfish, Carassius