Studies on Sylvatic Echinococcosis. III. Host Occurrence and Geographic Distribution of Echinococcus multilocularis in the North Central United States

Abstract

Studies were made on the sylvatic occurrence and geographic distribution of Echinococcus multilocularis Leuckart, 1963, in the north central states. During the 1965-69 period, 7,898 mammals, representing 32 species, were examined for the parasite. The adult cestode was found in the coyote (new natural host record) and red fox, and its larva in the deer mouse, meadow vole, and feral house mouse with the latter rodent constituting a new natural host record for E. multilocularis in North America. Infected mammals were found in Iowa, Montana, South Dakota, Minnesota, and North Dakota. Iowa, Montana, and South Dakota constitute new locality records for the parasite, representing considerable extensions of the cestode's known geographic range in the continental United States. The epidemiological and epizootiological significance of these findings are reviewed. The examination of numerous species of mammals, mainly wildlife, disclosed an enzootic occurrence of the cestode, Echinococcus multilocularis Leuckart, 1863, in Iowa, Minnesota, North Dakota, South Dakota, and eastern Montana. That this medically important cestode occurs sylvatically over an extensive geographic area and develops normally in a wide range of hosts in the north central United States has been confirmed. The purpose of this paper is to summarize these findings, with remarks on their epidemiological significance. Some of the data presented herein have been reported in previous papers (Leiby, 1965; Carney and Leiby, 1968). These papers and other reports on the sylvatic occurrence of E. multilocularis in the conterminous United States and southern Canada are summarized in Table I. MATERIALS AND METHODS During 5 years, 1965-69, a total of 7,898 mammals, collected by the writers and personnel of various federal and state agencies in Iowa, Minnesota, Montana, North Dakota, and South Dakota, was examined for E. multilocularis. The following were represented: short-tailed shrew, Blarina brevicauda (Say); coyote, Canis latrans Say; Richardson's ground squirrel, Citellus richardsonii (Sabine); thirteen-lined ground squirrel, C. tridecemlineatus (Mitchell); Gappers' red-backed mouse, Clethrionomys gapperi (Vigors); Ord's kangaroo rat, DipodReceived for publication 27 January 1970. * This work was supported by Public Health Service Grant 5 RO1 AI-06633, from the NIAID. t Present address: Department of Parasitology, Naval Medical Research Institute, National Naval Medical Center, Bethesda, Maryland 20014. omys ordii Woodhouse; porcupine, Erethrizon dorsatum (L.); least chipmunk, Eutamias minimus (Bachman); bobcat, Felis rufa Schreber; striped skunk, Mephitis mephitis (Schreber); prairie vole, Microtus ochrogaster (Wagner); meadow vole, M. pennsylvanicus Ord; house mouse, Mus musculus L.; ermine, Mustela erminea (Bonaparte); northern grasshopper mouse, Onychomys leucogaster (Wied-Neuwied); olive-backed pocket mouse, Perognathus fasciatus Wied-Neuwied; plains pocket mouse, P. flavescens Merriam; hispid pocket mouse, P. hispidus Baird; white-footed mouse, Peromyscus leucopus (Fisher); deer mouse, P. maniculatus (Wagner); raccoon, Procyon lotor (L.); Norway rat, Rattus norvegicus (Berkenhout); western harvest mouse, Reithrodontomys megalotis (Allen); arctic shrew, Sorex arcticus Kerr; badger, Taxidea taxus (Schreber); northern pocket gopher, Thomomys talpoides (Richardson); gray fox, Urocyon cinereoargenteus (Schreber); red fox, Vulpes vulpes L.; meadow jumping mouse, Zapus hudsonius ( Zimmerman); western jumping mouse, Z. princeps Allen; domestic dog and cat. Carnivores were examined for adult E. multilocularis with precautions taken to avoid contamination of personnel and the laboratory. Instrument and specimen containers were opened prior to necropsy. Disposable gloves were worn during necropsy and the small intestine carefully placed in the specimen container. Instruments were returned and gloves removed before closing the containers. Specimens were refrigerated in ice chests and taken to the laboratory where they were frozen until examined. The adult worms were obtained by scraping the contents and lining of the small intestine into tap water, after which the cestodes were washed and concentrated by decantation. Their presence was determined by the aid of a dissecting microscope or macroscopically with a high-intensity light against a black background. When present in small numbers, the cestodes were more readily detected by the latter method. The specimens were fixed in 10% formalin and stained with Mayer's carmalum.