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Diseases of Aquatic Organisms

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DAO 126:13-23 (2017)  -  DOI:

Exposure of harbour seals Phoca vitulina to Brucella in declining populations across Scotland

Joanna L. Kershaw1,*, Emma J. Stubberfield2, Geoffrey Foster3, Andrew Brownlow3, Ailsa J. Hall1, Lorraine L. Perrett2

1Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, St Andrews, Fife, KY16 8LB, UK
2Dept. of Bacteriology, Animal and Plant Health Agency (APHA), New Haw, Addlestone, Surrey, KT15 3NB, UK
3Scottish Marine Animals Strandings Scheme, SAC Consulting Veterinary Services, Inverness, IV2 4JZ, UK
*Corresponding author:

ABSTRACT: Since 2000 there has been a major decline in the abundance of Scottish harbour seals Phoca vitulina. The causes of the decline remain uncertain. The aim of this study was to establish the extent to which the seals in the regions of greatest decline have been exposed to Brucella, a bacterial pathogen that causes reproductive failure in terrestrial mammalian hosts. Tissues from dead seals collected between 1992 and 2013 were cultured for Brucella (n = 150). Serum samples collected from live capture-released seals (n = 343) between 1997 and 2012 were tested for Brucella antibodies using the Rose Bengal plate agglutination test (RBT) and a competitive enzyme-linked immunosorbent assay (cELISA). In total, 16% of seals cultured had Brucella isolated from one or more tissues, but there were no pathological signs of infection. The cELISA results were more sensitive than the RBT results, showing that overall 25.4% of seals were seropositive, with the highest seroprevalence in juveniles. As there was no evidence of either a higher seroprevalence or higher circulating antibody levels in seropositive animals in the areas with the greatest declines, it was concluded that Brucella infection is likely not a major contributing factor to recent declines. However, the consistently high proportion of seals exposed to Brucella indicates possible endemicity in these populations, likely due to B. pinnipedialis, which has demonstrated a preference for pinniped hosts. Importantly, given the close proximity between seals, humans and livestock in many areas, there is the potential for cross-species infections.

KEY WORDS: Pinnipeds · Brucella · Disease · Cultures · Seroprevalence · Antibodies · ELISA · Rose Bengal plate agglutination test

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Cite this article as: Kershaw JL, Stubberfield EJ, Foster G, Brownlow A, Hall AJ, Perrett LL (2017) Exposure of harbour seals Phoca vitulina to Brucella in declining populations across Scotland. Dis Aquat Org 126:13-23.

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