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1.02.2016

Analysis of Salmonella strains in Scottish grey seals raises concerns of microbial marine pollution

Scottish grey seal pups are found to be infected with forms of Salmonella bacteria, similar to those isolated from livestock and humans, according to a new study.

The study, led by researchers from the Moredun Research Institute, Edinburgh in collaboration with the Sea Mammal Research Unit, University of St Andrews; SAC Consulting Veterinary Services, Inverness; The Scottish Marine Animal Stranding Scheme, Inverness; the Scottish Salmonella, Shigella and Clostridium difficile Reference Laboratory, New Lister Building, Glasgow and the Royal Zoological Society of Scotland, Edinburgh was recently published in the Journal Environmental Microbiology1

The team investigated the prevalence and origin of Salmonella in free-ranging and stranded grey seal pups, comparing Salmonella isolated from the grey seals with strains from human cases, livestock, wild mammals and birds. 

Analysis of the different strains found close similarities with those found in terrestrial mammals, including cattle and humans, alluding to concerns of possible environmental pollution from activities such as farming and sewerage discharge.

Dr Johanna Baily of Moredun Research Institute, which led the research, said: “Finding these Salmonella isolates in large marine mammals along our coastlines raises concerns of land-sea transfer of both human and livestock pathogens. We need to know more about how these bacteria have spread to the marine environment and what threat they represent for our native marine mammals.”

The research found:

  • Salmonellawas present in over a fifth of all seal pups sampled: 37 out of 175. 
  • Live pups exposed to sea water were found to be almost 4 times more likely to carry Salmonella compared to those not exposed to sea water.
  • Three types of Salmonella were found; S.Bovismorbificans (18% of seals sampled) which is occasionally found in cattle, S. Typhimurium (~2%) similar to a type found in garden birds; and S. Haifa (~1%) which is also found in humans.

 

Dr Ailsa Hall, Director of the Sea Mammal Research Unit, added: “This study gives us an important insight into the factors affecting the survival of grey seal pups and the role that bacterial infection may play. Understanding the causes of morbidity and mortality in this species is key to improving our ability to interpret changes in the abundance and distribution of grey seals in the UK.”

Dr Geoff Foster of SAC Consulting Veterinary Services, Inverness commented: “This work expands on current knowledge of the ecology of an important group of pathogenic bacteria for man and animals. Our ongoing work with animal livestock, wild mammals and birds, alongside interactions with human health bodies, continues to explore such relationships, which are of significance for animal and public health.”

Dr Johanna Baily and Dr Mark Dagleish from Moredun Research Institute, Edinburgh and Dr Ailsa Hall of the Sea Mammal Research Institute, University of St Andrews collaborated with Dr Geoff Foster, SAC Consulting Veterinary Services in Inverness, the Scottish Marine Animal Stranding Scheme, the Scottish Salmonella, Shigella and Clostridium difficile Reference Laboratory at the Glasgow Royal Infirmary and the Royal Zoological Society of Scotland in Edinburgh.