Prevalence and molecular characterisation of Acanthocephala in pinnipedia of the North and Baltic Seas

Abstract

Harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) are final hosts of acanthocephalans in the German North and Baltic Seas. Parasitic infections in seals can cause pathological changes, which may result in deteriorated health of the host. Common gastrointestinal parasites of harbour and grey seals are acanthocephalans and a number of 275 of 2460 (11.2%) investigated seals from 1996 to 2013 were infected with Corynosoma spp. (Acanthocephala, Polymorphidae). The prevalence showed a wave-like pattern: it increased from 1.2% and 0.4% in 1996 and 1997, respectively, to 23.9% during the second phocine distemper epizootic in 2002 and decreased to 6.2% in 2004. In 2005, prevalence peaked again with 25.0% followed by a decrease to 9.3% in 2009 and an increase to 38.5% in 2012. Statistical analysis revealed that harbour seals originating from the North Sea showed a higher prevalence than grey seals, whereas no significant difference between grey and harbour seals from the Baltic Sea was observed. Furthermore, juvenile pinnipedia from the North Sea were significantly less infected with Corynosoma spp. than seals older than seven month. Molecular species identification as well as phylogenetic relationship analysis among the detected Corynosoma species were achieved by sequencing and comparisons of the ribosomal ITS1-5.8S-ITS2-complex and cytochrome-c-oxidase I gene. Molecular analysis resulted in a newly arranged distribution of Acanthocephala in the North Sea as in contrast to previous studies, C. strumosum could not be confirmed as predominant species. Instead, C. magdaleni and a C. magdaleni isolate (isolate Pv1NS) with an atypical number of longitudinal rows of hooks at the proboscis were detected. Furthermore, morphological and molecular analyses indicate the possible finding of a cryptic species (Candidatus Corynosoma nortmeri sp. nov.).

Host records and geographical distribution of Corynosoma magdaleni, C. semerme and C. strumosum (Acanthocephala: Polymorphidae)

“…García-Varela et al (2005) concluded that the Corynosoma species found in the Caspian Sea is C. caspicum and not C. strumosum. Indeed, C. strumosum from the land-locked Caspian seal recorded by Amin et al 2011 was characterised with proboscis hooks and trunk spines distinct from other Northern European morphological descriptions (Nickol et al 2002, Waindok et al 2018, Leidenberger et al 2019), suggesting that they may not be conspecific. Surprisingly, Corynosoma caspicum Golvan and Mokhayer, 1973, described based on immature specimens from sturgeons in Caspian Sea (Golvan and Mokhayer 1973) and often found in three-spined stickleback (Gasterosteus aculeatus) (Niksirat et al 2006), has not yet been reported in Pusa caspica or another definitive host.…”

“…By contrast, C. semerme has a circumpolar distribution, having been reported from the Arctic Ocean, north Atlantic and north Pacific (e.g. Popov and Fortunato 1987, Kaimoto et al 2018, Waindok et al 2018 (Fig. 2).…”

“…In most of the Baltic Sea studies, C. semerme was the species most commonly found in seals, followed by C. magdaleni and only rare infections were found for C. strumosum (Nickol et al 2002, Sinisalo and Valtonen 2003, Leidenberger and Bäcklin 2008, Waindok et al 2018. Co-infections have been observed (Nickol et al 2002, Leidenberger and Bäcklin 2008, Leidenberger et al 2019, most commonly involving C. semerme and C. magdaleni (Sinisalo and Valtonen 2003, Leidenberger and Bäcklin 2008, Waindok et al 2018. Interestingly, land-locked seal species show no mixed infections, but only single infections, for example, Phoca hispida saimensis in Lake Saimaa only by C. magdaleni Geographical distribution of Corynosoma strumosum.…”

“…Aznar et al (2006) erected the genus Pseudocorynosoma Aznar, Pérez-Ponce de León and Raga, 2006 for the freshwater species. Recent phylogenetic analysis based on ribosomal ITS1-5.8S-ITS2 and COI sequences showed that Corynosoma spp., hosted by Pinnipedia and marine Mustelidae formed a monophyletic group (Waindok et al 2018).…”

“…The systematics of Corynosoma species from seals in northern Europe have recently been investigated using both molecular markers (Waindok et al 2018) and morphology (Leidenberger et al 2019). These studies have highlighted the limitations of using traditional morphological characters alone for diagnosing species.…”