Biologic Identification of the Cestode Echinococcus multilocularis Isolated from Foxes in North Dakota

Abstract

The eggs from Echinococcus multilocularis recovered from red foxes in North Dakota were fed to cotton rats (Sigmodon hispidus) and infection in this host was obtained. This is biological verification of the occurrence of this species in the continental United States. Adult cestodes isolated from red foxes (Vulpes vulpes) in North Dakota were identified morphologically by Leiby and Olsen (1964) as Echinococcus multilocularis, Leuckart, 1863. This was the first time this species had been found in the continental United States and marked an extension of its geographic range. Biologic and morphologic studies of the cystic stages which developed in an experimentally infected rodent host have confirmed the identification of the organisms as E. multilocularis, indistinguishable from the species isolated in Alaska (Rausch, 1956). Gravid worms collected in North Dakota were suspended in water and given by stomach cannula to groups of cotton rats (Sigmodon hispidus). Individual rats received 10 to 15 worms each. The first three rats were inoculated 2 days after receipt of the worm material; the second group of three was fed 7 days later, and the final group was fed after the adult worms and some of the expelled eggs had been stored in water in the cold for 3 weeks. All but one of the cotton rats became infected. Figure 1 is a picture of an animal autopsied 8 weeks after experimental infection with small cystic clumps of E. multilocularis which are typical for infections in cotton rats (Sadun et al., 1957). In this animal there were abundant scolices in the cysts, many of which were mature although the infection was only 8 weeks old. A second animal autopsied at 6 weeks also contained some mature cysts. The scolices in cysts from two 4-month-old infections were examined with low-power magnification and could not be differentiated from scolices collected from rats infected for the Received for publication 29 March 1965. * U. S. Department of Health, Education, and Welfare, Public Health Service, Communicable Disease Center, Atlanta, Georgia. t Minot State College, Minot, North Dakota. same length of time with the Alaskan isolates which are being maintained at the Communicable Disease Center. The number of scolices per cyst of the North Dakota isolate was more numerous than that of the Alaskan strain. Two animals died with heavy experimental infections. The number of rostellar hooks on the scolices of E. multilocularis recovered from two animals with primary infections autopsied 8 months after feeding varied from 24 to 33 with a mean of 26.9 hooklets. This is comparable to the observations made by Cameron (1960). When the scolices were washed and subinoculated by intraperitoneal injection into four young cotton rats and three young gerbils FIGURE 1. Experimental infection of a cotton rat (Sigmodon hispidus) with eggs of Echinococcus multilocularis collected from a red fox (Vulpes vulpes) in North Dakota, USA.