Infectious diseases in marine mammals from the North and Baltic Seas

Infectious diseases play a major role in the health of marine mammals and thus in the population development. The occurrence of infectious diseases is a natural factor in wildlife populations but may also be influenced by... [ view full abstract ]

Infectious diseases play a major role in the health of marine mammals and thus in the population development. The occurrence of infectious diseases is a natural factor in wildlife populations but may also be influenced by anthropogenic activities. A stranding network and monitoring program has been established in northern Germany (Schleswig-Holstein) in 1990 allowing to collect systematically by-caught and stranded marine mammals with an equal effort over time. Full necropsies, histopatholological, microbiological, virological and parasitological investigations were conducted. Results from 25 years of investigations showed that viral diseases in harbor seals only play a role during epidemics. The population of harbor seals was severely reduced during two phocine distemper outbreaks in 1988/1989 and 2002 as well as by a first H10N7 influenza mortality in 2014. Different ectoparasites (Insekts; crustacea) and endoparasites (cestoda, trematoda, acanthoceph, nematoda) are found including in the ear complex in harbor porpoises. However, nematodes of the respiratory tract cause the most severe lesions both for harbor porpoises and seals. While harbor seals seem to develop a life-time immunity to pulmonary nematodes after surviving the first 18 months of their life harbor porpoises are suffering lifelong from parasitic pulmonary diseases. More than 100 different bacteria and fungi were isolated from these marine mammals over the last decades. So far Brucella spp., Clostridium perfringens, Escherichia coli, Erysipelothrix rhusiopathiae, beta-hemolytic streptococci and Staphylococcus aureus were identified as the responsible primary or secondary bacteria for most of the lesions. Bordetella bronchiseptica and Streptococcus equi subsp. zooepidemicus were mostly isolated during viral epidemics. Marine mammals from the North and Baltic Seas suffer from a large variety of infectious diseases. The severity of lesions is higher when compared with areas of lower anthropogenic pressure. This indicates that the health status needs to be systematically monitored when managing a marine mammal population.