Wood mouse ( Apodemus sylvaticus L.) as intermediate host for Mesocestoides canislagopodis (Rudolphi, 1810) (Krabbe 1865) in Iceland

Mesocestoides canislagopodis is a common parasite of the arctic fox ( Vulpes lagopus ) in Iceland. In the past, household dogs ( Canis familiaris ) and cats ( Felis catus ) were also reported in Iceland to be infected. Recently, scolices of a non-maturing Mesocestoides sp . were detected in the intestines of the gyrfalcon ( Falco rusticolus ), and tetrathyridia were isolated in the body cavity of rock ptarmigan ( Lagopus muta ) and subsequently described. All stages were confirmed, using both morphological and molecular methods, to belong to the same species, M. canislagopodis . In the present study, post-mortem examination of wood mice ( Apodemus sylvaticus ), sampled in autumn 2014 on a farm in Northeast Iceland, revealed the presence of tetrathyridia in the peritoneal cavity and in the liver. Most tetrathyridia in the peritoneal cavity were free, but some were encapsulated in a thin connective tissue stroma and loosely attached to the inner organs. They appear as whitish, heart-shaped, flattened, unsegmented bodies with a slightly pointed posterior end. In the liver, tetrathyridia were seen as pale-tanned nodules embedded in the parenchyma. Comparative molecular analysis, both at the generic level (D1 domain LSU ribosomal DNA), and at the specific level (cytochrome c oxidase subunit I ( cox1 ) and 12S mitochondrial DNA), revealed that the tetrathyridia belonged to M. canislagopodis . A. sylvaticus represents a new second intermediate host record in Iceland, and the first description of a rodent as intermediate host for this species, thus participating in the life cycle of the parasite.