Echinophthirius horridus subsp. infections

Herzog, Insa, Wohlsein, Peter, Preuss, Anika, Gorb, Stanislav N., Pigeault, emi, Ewers, Christa, Prenger-Berninghoff, Ellen, Siebert, Ursula & Lehnert, Kristina, 2024, Heartworm and seal louse: Trends in prevalence, characterisation of impact and transmission pathways in a unique parasite assembly on seals in the North and Baltic Sea, International Journal for Parasitology: Parasites and Wildlife 23, pp. 100898-100898 : 100898-

4.3. Impact of E. horridus infections on health status

In this study, only seals with severe levels of lice infections displayed alopecia, intralesional bacteria and pustules. Similarly, folliculitis was only diagnosed in macroscopically infected skin, while pathological findings like lymphohistiocytic, perivascular dermatitis and hyperkeratosis were also found in uninfected skin, indicating background pathology unrelated to parasitic infection. Hyperkeratosis can be seen in a variety of conditions in marine mammals ( Migaki and Jones, 1983; Lipscomb et al., 2001), perivascular dermatitis is considered as one of the most unspecific patterns of inflammation ( Mauldin and Peters-Kennedy, 2016) and could be caused by other factors, e.g. increased hauling out in consequence of illness and weakness. Diagnosis directly linked to arthropod bites is impeded by similarities to other clinical conditions ( Steen et al., 2004; Mauldin and Peters-Kennedy, 2016). Severe cases of seal louse infection were accompanied by alopecia and anaemia ( Conlogue et al., 1980; Dailey, 2001), supporting the findings of this study, while mild infections only caused irritation ( Raga et al., 1997; Leidenberger et al., 2007). In terrestrial wildlife, swamp wallabies ( Wallabia bicolor ) with a moderate chewing lice infection showed similar histological changes to this study, like alopecia, hyperkeratosis and perivascular dermatitis ( Portas et al., 2009). However, histological data of wildlife infected with blood sucking lice are scarce. In elephant seals ( Mirounga leonine ), histological investigations revealed a high inflammatory skin reaction caused by the elephant seal louse (Lepidophthirius macrorhini) during moulting ( Leonardi et al., 2021b). The present study indicates an attachment of lice to not only the hair shaft but also using the infundibula of the hair follicle to secure their grasp close to the hair root. In conclusion, severe seal lice infection can result in inflammatory processes in the skin caused by mouthparts of parasites during a blood meal or claws during attachment and therefore has a considerable impact on the health status of harbour and grey seals. In contrast, mild infections were not associated with inflammatory processes.