Streptococcal Infections in Marine Mammals

Abstract

Marine mammals are sentinels for the marine ecosystem and threatened by numerous factors including infectious diseases. One of the most frequently isolated bacteria are beta-hemolytic streptococci. However, knowledge on ecology and epidemiology of streptococcal species in marine mammals is very limited. This review summarizes published reports on streptococcal species, which have been detected in marine mammals. Furthermore, we discuss streptococcal transmission between and adaptation to their marine mammalian hosts. We conclude that streptococci colonize and/or infect marine mammals very frequently, but in many cases, streptococci isolated from marine mammals have not been further identified. How these bacteria disseminate and adapt to their specific niches can only be speculated due to the lack of respective research. Considering the relevance of pathogenic streptococci for marine mammals as part of the marine ecosystem, it seems that they have been neglected and should receive scientific interest in the future.

Keywords: infectious diseases; marine mammals; streptococci.

Figure 1

Occurrence of streptococcal species described in different marine mammals. Streptococcal species that have been isolated and identified at least twice in pinnipeds (A) and cetaceans (B). (C) shows a world map indicating location of streptococcal species detected in marine mammals.

Figure 2

Schematic representation of the infection of marine mammals with (opportunistic) streptococci.

Figure 3

Possible ways how streptococci are introduced into marine environments and how they may be transmitted to and between marine mammals. Most indicated transmission routes are hypothetical based on general microbiological observations. In the other cases, there are studies showing that the transmission route is very likely or even confirmed. Hence, this figure displays scientific gaps that has still to be filled and where data are insufficient.