Echinococcus spp. Tapeworms in North America

Jacey Roche Cerda; Danielle Elise Buttke; Lora Rickard Ballweber


Emerging Infectious Diseases. 2018;24(2):230-235. 

In This Article

E. Multilocularis and Ae in the Contiguous United States

E. multilocularis tapeworms are also historically endemic in several northern states. During 1965–1969, Leiby et al.[40] examined 7,898 definitive and intermediate host mammals from eastern Montana, North and South Dakota, Minnesota, and Iowa. Among the definitive hosts, the authors found that 8.5% (131/1,540) of red fox and 4.1% (7/171) of coyotes examined were infected. In North Dakota, 55.3% of red fox were found infected in 1965, while only 7.3% were infected in 1968. No domestic cats (n = 35) or dogs (n = 88) were found to be infected.[40] However, in a subsequent report, Leiby and Kritsky[41] reported that 2 adult house cats from a homestead in North Dakota were infected with E. multilocularis tapeworms in 1971.

Of the numerous potential intermediate hosts examined by Leiby et al.,[40] only 3 species, the deer mouse (Peromyscus maniculatus), meadow vole (Microtus pennsylvanicus), and house mouse (Mus musculus), were found to have E. multilocularis cysts. Infected deer mice were found in all 5 states, with the highest number, 202/4,209 (4.8%), in North Dakota. Infected meadow voles were found only in Iowa and North Dakota, with 1.9% infected (20/1,033). Only 1/91 (1.1%) house mice examined, also from North Dakota, was infected. The reported infections may be an overly conservative estimate because data were obtained through visual examination of the carcasses for cysts; early or latent cysts may be too small for gross visualization.

In the 1980s, Ballard et al.[42,43] extended the known range of E. multilocularis tapeworms into Nebraska, Illinois, and Wisconsin, further indicating the endemic cycle in the north-central United States. Ten (27%) of 36 foxes were infected in Nebraska, 4 (10%) of 40 in Illinois, and 6 (8.3%) of 72 in Wisconsin.[42] In the mid-1990s, the known range expanded again when E. multilocularis infection was found in Michigan and Ohio.[44,45]

In 2000, Hildreth et al.[46] reported the results of a combined study of both wild canids and human trappers in South Dakota. The intestines of foxes trapped between 1987–1991, and of coyotes trapped between 1990–1991, were examined for the presence of E. multilocularis tapeworms. Results showed that 74.5% of foxes and 44.4% of coyotes were infected at the time of trapping. Because trappers are a population at extreme risk for AE, given their constant and extended contact with potentially infected wild canids, blood samples were obtained from 115 attendees of the South Dakota trappers meetings in 1990 and 1991. However, despite their high risk, none of the trappers showed evidence of infection.

Only 1 autochthonous case of AE has been confirmed in the contiguous United States, and that occurred in a 56-year-old woman from Minnesota.[47] The patient had never lived outside of Minnesota, and her travel history included only California, Hawaii, Florida, and Manitoba, Canada. Gamble et al.[47] asserted that she was most likely to have been infected through interaction with pet dogs allowed to consume rodents on the farm where she grew up.