Morphometric, molecular and histopathologic description of hepatic infection by <italic>Orthosplanchnus arcticus</italic> (Trematoda: Digenea: Brachycladiidae) in ringed seals (<italic>Pusa hispida</italic>) from Northwest Greenland.

For the first time in > 30 years of routine sampling under the Arctic Monitoring and Assessment Program, a parasite was found in the liver of ringed seals (<italic>Phoca hispida</italic>) collected near Qaanaaq (Thule), Northwest Greenland, in 2008 and 2014. Concerns regarding changes to parasite occurrence, possibly related to climate change and bioaccumulation of immunomodulating anthropogenic pollutants, spurred further investigations into parasite characterization, and implications for wildlife health and seal hunters. Microscopic, molecular, and morphometric analyses are presented herein. Of 40 seals, 6 (15%) were infected, and 5 of 6 of these seals had severe infections. The parasite was identified morphologically as <italic>Orthosplanchnus arcticus</italic> Odhner, <xref>1905</xref> (Trematoda; Digenea: Brachycladiidae<bold>)</bold>. Macro- and microscopic pathologic study indicated mild-to-severe biliary hyperplasia associated, stasis associated, and fibrosis associated with trematode infections. Molecular analysis of the trematode confirmed its classification within the Brachycladiidae using sequencing and comparing Internal Transcribed Spacer-1, mitochondrial-NADH Dehydrogenase 3, 18S ribosomal DNA, and Cyclooxygenase-1 regions. This is the first ever report of <italic>O. arcticus</italic> in ringed seals from Qaanaaq and is one of the most northern records of this parasite. We found significant liver pathology in severely infected seals, but its effects on health of seals in this population are unknown. Host-specificity and the lifecycle of <italic>O. arcticus</italic> are unknown, but transmission may involve subsistence and commercially harvested Arctic fish species. Further work is needed to answer these questions. Surveying parasites in Arctic wildlife is important in order to assess potential effects on wildlife and human health (i.e., zoonoses). [ABSTRACT FROM AUTHOR]