Fatal Streptococcus iniae Infection in a Juvenile Free-Ranging Short-Beaked Common Dolphin (Delphinus delphis)

Abstract

Streptococcus iniae (S. iniae) is a significant aquatic pathogen of farmed fish species, important zoonotic pathogen, and reported cause of disease in captive Amazon River dolphins (Inia geoffrensis) and a bottlenose dolphin (Tursiops truncatus). Here we report S. iniae as the cause of subcutaneous abscesses, sepsis and mortality in a juvenile free-ranging short-beaked common dolphin (Delphinus delphis) found deceased on a metropolitan Australian beach. Body surfaces were covered by multifocal, depressed, deep, irregular cutaneous ulcerations, which microscopically were characterised by ruptured subcutaneous abscesses with intralesional cocci. Routine microbiological investigations revealed a heavy growth of beta-haemolytic Streptococcus sp. identified as Streptococcus iniae in skin lesions as well as from heart blood, the latter supportive of sepsis. Tissues were negative for cetacean morbillivirus and no other disease processes were identified. S. iniae has not been reported in free-ranging marine mammals, nor in Australian delphinids, previously. More notably a pathogen of captive animals, this case report identifies S. iniae as a pathogen of wild dolphins also. In addition to expanding the host reservoir of a significant zoonotic pathogen, determining the source of infection as well as possible consequences for other marine mammals and wild and intensive fish stocks warrants further investigations.

Impacts of streptococcal infection on Nile tilapia Oreochromis niloticus in Egyptian farms with special reference to diagnosis and prevention

“…Other methods for detecting streptococcus bacteria, such as the RAPID, VITEX, API 20 STREP, and Rapid Strep 32 systems can also be applied (Facklam et al, 2005;Lau et al, 2006).Serological tests, such as the enzyme-linked immunosorbent assay is also used for identification purpose (Liu et al, 2014). For quick detection and identification of S. iniae, a monoclonal antibody-based indirect fluorescent antibody method was also used (Klesius et al, 2006;Souter et al, 2021).…”

“…Multi Locus Sequence Typing was also utilized for identification purposes (Lusiastuti et al, 2013;. Identification of streptococcus species is also done by the MALDI-TOF-MS technique (Kim et al, 2017;Souter et al, 2021).…”

Streptococcus iniae in aquaculture: a review of pathogenesis, virulence, and antibiotic resistance

“…Recent outbreaks of this infection were documented in aquaculture farms in Brazil and Mexico [ 24 , 25 ]. Although it is a significant pathogen in aquaculture, recent research has reported streptococcosis presence caused by this bacterium in marine mammals and fish, indicating that it could pose a risk to wild populations [ 26–29 ]. Moreover, genetic factors have been recently facilitating the emergence of variations that allow colonizing of new host tissues or even taxa, evasion strategies from the immune system in vaccinated hosts [ 21 ] besides antibiotic-resistant strain emergence [ 30–32 ].…”