Echinophthirius horridus

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-

3.1. E. horridus and A. spirocauda in harbour seals

Seal louse, E. horridus was found in 4% (26/659) of harbour seals between 2014 and 2021 ( Table 2). Twenty-four harbour seals were infected mildly with E. horridus , one moderately and one severely. Prevalence varied significantly between the sampling years ( Tables 2 and 3). No seal louse infection was detected in 2018 and 2019 ( Fig. 3 ). Age affects the seal louse prevalence in harbour seal significantly: older animals (> 18 month, AG 3) were more likely to be infected with seal lice ( Table 3). Neither sex, nor location, sampling month or decomposition status significantly affected the prevalence of E. horridus in harbour seals.

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A. spirocauda was found in 13% (79/613) of harbour seals between 2014 and 2021. Fifty-eight harbour seals were infected mildly with A. spirocauda , 20 moderately and one severely. The prevalence of A. spirocauda in harbour seals varied significantly ( Table 3) over the eight-year time span ( Fig. 3 , Table 2). In each study year, A. spirocauda prevalence in harbour seals was above 10% with the exception of 2019 whereas prevalence was at 3%. Additionally, a significant difference was found in the prevalence regarding sampling months. The highest prevalence occurred in harbour seals sampled during the winter months (20%), followed by autumn (14%), spring (10%) and summer (5%) ( Fig. 3 ). The implemented model did not show an effect caused by the age class, sex, and degree of decomposition or location. Two harbour seals showed a coinfection with E. horridus and A. spirocauda . In one harbour seal with severe lice infection alopecia and dermatitis were

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recorded. No macroscopical lesions associated with A. spirocauda infections were diagnosed in harbour seals (n = 79) investigated between 2014 and 2021.

Figures

Fig. 3. A: Prevalence of A. spirocauda and E. horridus in harbour seals in the North and Baltic Sea from 1996 to 2021, data from 1996 to 2013 according to Lehnert et al. (2016). B: Prevalence of A. spirocauda and E. horridus in harbour seals during the seasons in the North and Baltic Sea from 2014 to 2021.