The Seal Louse (Echinophthirius horridus) in the Dutch Wadden Sea: Investigation of Vector-Borne Pathogens and Morphological Adaptations

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 role of E. horridus in vector-borne diseases of seals in the Dutch Wadden Sea and to attribute to its morphological features of environmental adaptation.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. In addition E. horridus-adult and -eggs were analysed by scanning electron microscopy (SEM).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. SEM analyses of E. horridus-adults and -eggs brought out more clearly unique morphological features, such as ‘lock-like’ claws, setae-covered cuticle as well as vaulted nit lids carrying micropyles for respiration, which all demonstrate the adaption of this ectoparasite to its semiaquatic host and the marine environment.Conclusions: Our findings support the vector role of seal lice in transmission of A. spirocauda, Mycoplasma spp. and A. phagocytophilum and presented more detailed images of their morphological adaptations to the semiaquatic lifestyle of their hosts. As the vector-borne 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.

I've got you under my skin: inflammatory response to elephant seal's lice

“…In the marine environment, echinophthiriids lice were identified as the intermediate vectors of filarial worms (Leidenberger et al ., 2007) and also as the reservoirs of invasive pathogens such as Mycoplasma sp. (Hirzmann et al ., 2020). Linn et al .…”

“…In the marine environment, echinophthiriids lice were identified as the intermediate vectors of filarial worms (Leidenberger et al, 2007) and also as the reservoirs of invasive pathogens such as Mycoplasma sp. (Hirzmann et al, 2020). Linn et al (2001) presented evidence for L. macrorhini as the source of the transmission of an alphavirus to Southern elephant seals at Macquarie Island, Antarctica.…”