High Prevalence of Human Liver Infection by Amphimerus spp. Flukes, Ecuador

Manuel Calvopiña, William Cevallos, Hideo Kumazawa, and Joseph Eisenberg

Author affiliations: Universidad Central del Ecuador Centro de Biomedicina, Quito, Ecuador (M. Calvopina, W. Cevallos); Kochi University School of Medicine, Kochi, Japan (H. Kumazawa); University of Michigan, Ann Arbor, Michigan, USA (J. Eisenberg)

Abstract

Amphimerus spp. flukes are known to infect mammals, but human infections have not been confirmed. Microscopy of fecal samples from 397 persons from Ecuador revealed Opisthorchiidae eggs in 71 (24%) persons. Light microscopy of adult worms and scanning electron microscopy of eggs were compatible with descriptions of Amphimerus spp. This pathogen was only observed in communities that consumed undercooked fish.

The genus Amphimerus Barker 1911 infects mammals from the Americas, including Canada, the United States, Costa Rica, Panama, Colombia, Brazil, and Peru. Eleven species are reported (1–7). In Ecuador, a trematode resembling Amphimerus spp. but identified as Opisthorchis guayaquilensis has been reported (8,9).

Amphimerus spp. are parasitic liver flukes in the bile ducts of mammals, birds, and reptiles (1). Although these digenetic trematodes of the Opisthorchiidae family are closely related to the genera Clonorchis and Opisthorchis, there are morphologic differences. The vitellaria in adult Amphimerus spp. trematodes are distributed in 4 groups, 2 anterior and 2 posterior; the latter groups extend beyond the posterior testis; the ventral sucker is larger than the oral, and the testes are rounded or slightly lobulated. In contrast, the vitellaria in Clonorchis and Opisthorchis spp. worms exist only in front of the testes. Additionally, Clonorchis spp. trematodes have 2 large highly branched testes; testes in Opisthorchis spp. trematodes are always lobulated (1,2). The eggs of the flukes from these genera can be differentiated only by using scanning electron microscopy (SEM). Definitive diagnosis using light microscopy of the flukes of the Opisthorchiidae family, therefore, is not possible unless the adult worm is collected and identified. Through isolation of adult worms and SEM of eggs, we found a high prevalence of human infection with a trematode of the genus Amphimerus in Ecuador.

Suggested citation for this article: Calvopiña M, Cevallos W, Kumazawa H, Eisenberg J. High prevalence of human liver infection by Amphimerus spp. flukes, Ecuador. Emerg Infect Dis [serial on the Internet]. 2011 Dec [date cited]. http://dx.doi.org/10.3201/eid1712.110373