The seal louse (Echinophthirius horridus) in the Dutch Wadden Sea: investigation of vector-borne pathogens 

Abstract Background: Belonging to the anopluran family Echinophthiriidae, Echinophthirius horridus, the seal louse, has been reported to parasitize a broad range of representatives of phocid seals. So far, only few studies focused on vector function of echinophthiriid lice and knowledge on their role in pathogen transmission is still scarce. The current study aims to investigate the possible vector role of E. horridus parasitizing seals in the Dutch Wadden Sea.Methods: More than 1200 E. horridus seal lice were collected from 54 harbour seals (Phoca vitulina) and one grey seal (Halichoerus grypus) during their rehabilitation period in the Sealcentre Pieterburen, the Netherlands. DNA was extracted from pooled seal lice of individual seals for molecular detection of the seal heartworm Acanthocheilonema spirocauda, the rickettsial intracellular bacterium Anaplasma phagocytophilum, and Mycoplasma spp. using PCR assays.Results: Seal lice from 35% of the harbour seals (19/54) and from the grey seal proved positive for A. spirocauda. The seal heartworm was molecularly characterised and phylogenetically analysed for the first time (rDNA, cox1). A nested PCR was developed for the cox1 gene to detect A. spirocauda stages in seal lice. A. phagocytophilum and a Mycoplasma species previously identified from a patient with disseminated ‘seal finger’ mycoplasmosis were detected the first time in seal lice. Conclusions: Our findings support the potential vector role of seal lice in transmission of A. spirocauda, and reveal new insights into the spectrum of pathogens occurring in seal lice. As these pathogens might have detrimental effects on the health of seal populations further epidemiological investigations on infections due to these pathogens in seals should be conducted.