"Salmon poisoning" disease. IV. Transmission of the disease to dogs by Nanophyetus salmincola eggs.

The presence of the etiologic agent of "salmon poisoning" disease, Noorickettsia helminthoeca, was demonstrated in eggs of the trematode vector, Nanophyetus salmincola. Three dogs were given 100,000 and one dog 82,000 ground fluke eggs by intraperitoneal injection. The four animals developed "salmon poisoning" disease and died. One of these dogs had been given 100,000 intact eggs previously; this inoculum did not produce the disease. Two dogs that received either intact or ground adult flukes intraperitoneally also died from "salmon poisoning" disease. Noninjected control dogs remained healthy in all instances. Lymph nodes removed from a dog that had been injected with 82,000 ground eggs and had died from the disease were injected intraperitoneally into a susceptible dog. After this dog developed signs of "salmon poisoning" disease, it was given antibiotic therapy and allowed to recover. This animal was shown to be immune to the disease by challenge with N. salmincola metacercariae from fish. A susceptible control dog given the same number of metacercariae developed the disease and died. Intracytoplasmic inclusion bodies were seen in stained lymph node cells from all dogs that developed the disease. "Salmon poisoning" disease (SPD) has been produced in susceptible dogs by intraperitoneal (IP) injection of all stages of the trematode vector, Nanophyetus salmincola, except the eggs and miracidia. Simms et al. (1931) and Simms and Muth (1933) produced SPD in dogs by injecting intact and ground, respectively, adult flukes that were recovered from intestines of infected dogs. Simms et al. (1932) produced the disease in dogs by injecting metacercariae from salmonid fishes, and Philip et al. (1954b) by injecting ground livers of the snail host Oxytrema silicula that contained cercariae. Transovarian transmission of the etiologic agent into fluke eggs has been suggested by Philip et al. (1954a) and Philip (1958). These authors indicated that even though experimental proof was lacking, the circumstantial evidence was overwhelmingly in favor of this type of transmission in the fluke. Philip et al. (1954b) tested for presence of the agent in fluke eggs by injecting (IP) 14,000 ground eggs into one dog and 51,000 into another. Received for publication 24 April 1967. * This investigation was supported in part by Public Health Service Research Grant 5 RO1 AI06599-03, from the NIAID. Technical Paper No. 2285, Oregon Agricultural Experiment Station. This study is a portion 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 Doctor of Philosophy. Neither dog developed the disease. Philip (1958) suggested that this experiment should be repeated using larger numbers of eggs and different methods of preparation; however, no additional attempts have been made. Thus, there has continued to the present time an uncertainty as to where N. helminthoeca entered the fluke's life cycle. This paper reports the results of a study undertaken to determine if the causative agent of SPD is present within the eggs of N. salmincola. MATERIALS AND METHODS Experimental animals The 13 dogs used in these experiments were obtained when 4 to 5 weeks old from the Benton County pound in Oregon. Kennel procedures and methods for recording data similar to those reported by Andersen (1964) and McKelvie and Shultz (1964) were used for maintenance of the animals. Body temperature and weight of each dog were recorded daily at approximately 9:00 AM. All of the animals used in Experiments I and II were female littermates of pointer-beagle origin with exception of donor dog (D-I) for Experiment I; this animal was also a female and of approximately the same age as the others but a mongrel. Dogs used in Experiment III were all female littermates of labrador-pointer origin with exception of (D-8) and (D-10). Dog (D-8) was a male littermate of other dogs used in Experiment III, and (D-10) was a mongrel male of approximately the same age as the others. The animals were not vaccinated against any ca ine diseases and had not been exposed to SPD prior to these experiments. All animals were at least 4 months old when used in an experiment.