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 parasitise a broad range of representatives of phocid seals. So far, only a few studies have focused on the vector function of echinophthiriid lice, and knowledge about their role in pathogen transmission is still scarce. The current study aims to investigate the possible vector role of E. horridus parasitising seals in the Dutch Wadden Sea. Methods E. horridus seal lice were collected from 54 harbour seals (Phoca vitulina) and one grey seal (Halichoerus grypus) during their rehabilitation period at 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 the cell wall-less bacteria 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 (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 for the first time, to our knowledge, in seal lice. Conclusions Our findings support the potential vector role of seal lice in the transmission of A. spirocauda and reveal new insights into the spectrum of pathogens occurring in seal lice. Studies on vector competence of E. horridus, especially for bacterial pathogens, are essentially needed in the future as these pathogens might have detrimental effects on the health of seal populations. Furthermore, studies on the vector role of different echinophthiriid species infecting a wide range of pinniped hosts should be conducted to extend the knowledge of vector-borne pathogens.

Genetic diversity of vector-borne pathogens in spotted and brown hyenas from Namibia and Tanzania relates to ecological conditions rather than host taxonomy

“…The Acanthocheilonema species labelled A. reconditum -like in Figure 5 from domestic dogs in India was also demonstrated to develop to infective third larvae in H. longipennis [ 40 ]. The seal heartworm A. spirocauda is transmitted by the seal louse Echinophthirius horridus [ 110 , 111 ]. It is interesting that adults of the latter species are not located in sites where they cause little damage, such as the peritoneal cavity ( A. dracunculoides ) or the subcutis ( A. reconditum ), but in the heart, where they can potentially cause anorexia and fatigue that may lead to more severe heart and lung complications and sometimes death [ 112 ].…”

Surveillance for Zoonotic Pathogens and Inuit Qaujimajatuqangit of Ringed Seals (nattiit) (Pusa hispida) in Frobisher Bay and Eclipse Sound, Nunavut, Canada

“…E. rhusiopathiae is ubiquitous in nature and an opportunistic pathogen (Wang et al, 2010;Forde et al, 2016), and widespread mortality events caused by this bacterium have been described among muskoxen (Ovibos moschatus) on Victoria Island and Banks Island, western Nunavut (Kutz et al, 2015;Forde et al, 2016). Although we did not notice, or look for, lice on pelts of harvested nattiit, the unsolicited comment by some LKHs that they see them regularly is interesting in view of the potential role of ectoparasites, including seal lice, as vectors of some pathogens (Chirico et al, 2003;Hirzmann et al, 2021). Conversely, fish can harbor this bacterium on their epidermal mucus and may represent another source of exposure for seals (Wang et al, 2010).…”

Rickettsiales in the WHO European Region: an update from a One Health perspective

“…Regarding lice, Rickettsia prowazekii was identified in the louse Pediculus humanus capitis in Turkey; this louse was taxonomically identified as P. h. capitis by DNA analysis and comparison with the reference strain in the GenBank (AY239286) [ 35 ]. The louse Echinophthirius orridus was also collected from a seal in The Netherlands, and subsequent study of Rickettsiales DNA showed positivity for Anaplasma phagocytophilum [ 36 ]. The rodent lice Polypax serrata [ 37 ] and Hoplopleura affinis were found to be infected with R. helvetica [ 37 ].…”