Emergence of the Zoonotic Biliary Trematode Pseudamphistomum truncatum in Grey Seals (Halichoerus grypus) in the Baltic Sea

Abstract

The biliary trematode Pseudamphistomum truncatum parasitizes a wide range of fish-eating mammals, including humans. Here we report the emergence of this parasite in grey seals (Halichoerus grypus) in the Baltic Sea. One hundred eighty-three of 1 554 grey seals (11.9%) examined from 2002–2013 had detectable hepatobiliary trematode infection. Parasite identification was confirmed as P. truncatum by sequencing the ITS2 region of a pool of five to 10 trematodes from each of ten seals collected off the coast of seven different Swedish counties. The proportion of seals parasitized by P. truncatum increased significantly over time and with increasing age of seals. Males were 3.1 times more likely to be parasitized than females and animals killed in fishery interactions were less likely to be parasitized than animals found dead or hunted. There was no significant difference in parasitism of seals examined from the Gulf of Bothnia versus those examined from the Baltic Proper. Although the majority of infections were mild, P. truncatum can cause severe hepatobiliary disease and resulted in liver failure in at least one seal. Because cyprinid fish are the second intermediate host for opisthorchiid trematodes, diets of grey seals from the Baltic Sea were analysed regarding presence of cyprinids. The proportion of gastrointestinal tracts containing cyprinid remains was ten times higher in seals examined from 2008 to 2013 (12.2%) than those examined from 2002 to 2007 (1.2%) and coincided with a general increase of trematode parasitism in the host population. The emergence and relatively common occurrence of P. truncatum in grey seals signals the presence of this parasite in the Baltic Sea ecosystem and demonstrates how aquatic mammals can serve as excellent sentinels of marine ecosystem change. Investigation of drivers behind P. truncatum emergence and infection risk for other mammals, including humans, is highly warranted.

High prevalence of zoonotic trematodes in roach (Rutilus rutilus) in the Gulf of Finland

“…Zoonotic Pseudamphistomum truncatum and Metorchis bilis (family Opistorchiidae) have been found in the coastal area in one of their final hosts, the fox [ 8 ]. Grey seals ( Halichoerus grypus ) in the Baltic Sea have also been observed to commonly carry P. truncatum [ 8 , 9 ]. High prevalence (75%) of Pseudamphistomum truncatum in the roach in the Russian waters of the Gulf of Finland has been recently reported [ 10 ].…”

Anthropozoonotic Parasites Circulating in Synanthropic and Pacific Colonies of South American Sea Lions (Otaria flavescens): Non-invasive Techniques Data and a Review of the Literature

“…type 1 were already detected by Hermosilla et al (2016a) in synanthropic sea lion feces, and size and shape are morphologically similar to eggs of members of trematode families Opisthorchiidae and Heterophyidae (Ditrich et al, 1992), which includes the genus Ascocotyle. Members of Opistorchiidae have never been reported parasitizing O. flavescens so far, however, other pinnipeds were described to function as definitive hosts (Chai et al, 2005;Heckmann and Halajian, 2012;Neimanis et al, 2016). Depending on species and localization of adult trematodes, dimension of infections in marine mammals can range from low enteritis up to necrosis of parenchyma of affected organs (Geraci and St. Aubin, 1987).…”

An annotated checklist of the eukaryotic parasites of humans, exclusive of fungi and algae

“…Pseudamphistomum truncatum (Rudolphi, 1819) Geographic distribution. Europe, Asia (Neimanis et al 2016). Natural hosts.…”

“…Definitive hosts are carnivores, including cats, pinnipeds, and mustelids. Zoonotic in humans ( Neimanis et al 2016 ).…”