# Diphyllobothrium stemmacephalum infections in harbor porpoises (Phocoena Phocoena) in German waters

## TL;DR

This study found low prevalence of Diphyllobothrium stemmacephalum in harbor porpoises in German waters and confirmed it as a parasite that can infect humans.

## Contribution

Molecular confirmation of D. stemmacephalum in harbor porpoises and its low pathogenic impact in the region.

## Key findings

- Low prevalence (3%) of Diphyllobothrium cestodes in harbor porpoises across German North and Baltic Seas.
- Molecular identification confirmed the cestode species as D. stemmacephalum.
- Infections showed mild effects on porpoise health and no significant impact on cause of death.

## Abstract

Harbor porpoises (Phocoena) are definitive hosts for intestinal Diphyllobothrium sp. cestodes, zoonotic parasites with a heterogeneous life cycle and fishes as second intermediate hosts. Prevalence and level of infection of Diphyllobothrium cestodes in 661 dead-found harbor porpoises from the German North and Baltic Seas within a 30-year period were investigated. Molecular species identification of cestodes was carried out, using ribosomal and mitochondrial gene markers. Pathogenic impact of cestodes on intestinal tissue was analyzed by using review of histopathological records. With 18 cestode-infected harbor porpoises, prevalence was low (3 %) in both ecosystems. Infected animals were mostly young and exhibited mild infection levels. Cestode infection did not contribute significantly to cause of death and disease of the infected individuals and histopathological alterations of intestinal tissue were mostly mild. Tapeworms were molecularly identified as D. stemmacephalum. The findings validate past morphological records in the study area for the first time and confirm harbor porpoises as definitive hosts for D. stemmacephalum. D. stemmacephalum can accidentally infect humans. Future research on cetacean definitive host populations and species-specificity as well as life cycle and intermediate host species of D. stemmacephalum is crucial for a risk assessment in the sense of the One Health concept.

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•Low prevalence of intestinal cestodes in harbor porpoises from German waters.•Molecular identification of cestodes as Diphyllobothrium stemmacephalum.•No ecosystem-specific variation or time trends in infection.•No significant impact of D. stemmacephalum on harbor porpoises' health.

Low prevalence of intestinal cestodes in harbor porpoises from German waters.

Molecular identification of cestodes as Diphyllobothrium stemmacephalum.

No ecosystem-specific variation or time trends in infection.

No significant impact of D. stemmacephalum on harbor porpoises' health.