Abstract
Marine mammals have been recognized as sentinels for oceans and human health, with infectious diseases being one aspect of their indicator potential.1 This is relevant in light of the increase of emerging diseases that must be expected due to climate change.2 Marine mammals as apex predators reflect the entire marine ecosystem.1 Furthermore, marine mammals and humans share the same environment, eat the same food, and might come in close contact during rescue and rehabilitation. Thus, health surveillance of marine mammals is an important tool, both under conservation implications and under the One Health approach.
Here, we investigated live-caught harbor and grey seals in the German Wadden Sea of Schleswig-Holstein. From 1992 to 2022, around 650 animals were caught and sampled on sandbanks or beaches before they were directly released back into the wild. Samples included blood for serology as well as swabs from the eye, nose, mouth, rectum, and vagina. Virological and microbiological screening varied over time, becoming constant within the last decade. While no phocine distemper virus (PDV) infection was detected, individual harbor seals still carried antibodies, although the last PDV epidemic was 20 years ago.3 Herpesvirus infections appear to be widespread in the Wadden Sea harbor and grey seal populations. Both viral infections as well as antibodies were detected in the majority of animals. Sequencing showed a high prevalence of PhHV-7, a moderate prevalence of PhHV-1 and PhHV-5, and a low prevalence of PhHV-2. Influenza screening revealed no evidence of an active infection, but serum-positive animals occurred regularly. Investigated zoonotic bacterial infections included brucellosis, erysipelas, and leptospirosis, with occasional findings of antibodies.
In the German North Sea, dead stranded harbor seals have been shown to frequently carry Brucella spp. and Erysipelothrix rhusiopathiae.4 In 2021, three harbor seals from the German North Sea died due to an infection with highly pathogenic avian influenza virus (HPAIV) H5N8.5 We postulate that to obtain an overview of ongoing infections in wildlife populations, health monitoring of alive, assumably healthy individuals, is an important supplementation to the screening of dead stranded animals. Furthermore, this study highlights the need for continuous monitoring of infectious diseases in marine mammals, both for conservation aspects as well as with regard to the One Health approach.
Acknowledgements
We wish to thank all the people involved in the seal catches and sampling procedures. Seal catches in the Wadden Sea were funded by the State Agency for Coastal Protection, National Park and Marine Conservation (LKN). Sampling activities were performed under the permits 70-6/07, 11-2/19, 24-4/21.
*Presenting author
Literature Cited
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