Abstract
A high prevalence of Brucella pinnipedialis serology and bacteriology positive animals has been found in the Northeast Atlantic stock of hooded seal ( Cystophora cristata ); however no associated gross pathological changes have been identified. Marine mammal brucellae have previously displayed different infection patterns in human and murine macrophages. To investigate if marine mammal Brucella spp. are able to invade and multiply in cells originating from a presumed host species, we infected alveolar macrophages from hooded seal with a B . pinnipedialis hooded seal isolate. Hooded seal alveolar macrophages were also challenged with B . pinnipedialis reference strain (NCTC 12890) from harbor seal ( Phoca vitulina ), B . ceti reference strain (NCTC 12891) from harbor porpoise ( Phocoena phocoena ) and a B . ceti Atlantic white-sided dolphin ( Lagenorhynchus acutus ) isolate (M83/07/1), to evaluate possible species-specific differences. Brucella suis 1330 was included as a positive control. Alveolar macrophages were obtained by post mortem bronchoalveolar lavage of euthanized hooded seals. Phenotyping of cells in the lavage fluid was executed by flow cytometry using the surface markers CD14 and CD18. Cultured lavage cells were identified as alveolar macrophages based on morphology, expression of surface markers and phagocytic ability. Alveolar macrophages were challenged with Brucella spp. in a gentamicin protection assay. Following infection, cell lysates from different time points were plated and evaluated quantitatively for colony forming units. Intracellular presence of B . pinnipedialis hooded seal isolate was verified by immunocytochemistry. Our results show that the marine mammal brucellae were able to enter hooded seal alveolar macrophages; however, they did not multiply intracellularly and were eliminated within 48 hours, to the contrary of B. suis that showed the classical pattern of a pathogenic strain. In conclusion, none of the four marine mammal strains tested were able to establish a persistent infection in primary alveolar macrophages from hooded seal.
Highlights
Brucellosis, caused by the facultative intracellular bacteria Brucella spp., is a contagious disease known to affect a wide range of animal species, and some members of the genus are zoonotic
We present the results of infecting hooded seal alveolar macrophages with marine mammal Brucella spp. in vitro
Cells retrieved by BAL in hooded seals were found to be positive for the monocyte/macrophage membrane marker CD14 [34], as well as the pan-leukocytic marker CD18 [35]
Summary
Brucellosis, caused by the facultative intracellular bacteria Brucella spp., is a contagious disease known to affect a wide range of animal species, and some members of the genus are zoonotic. Gross pathology in association with Brucella infection in marine mammals is reported exclusively in cetaceans, mainly in the central nervous system and the reproductive organs [4,5,6]. The hooded seal (Cystophora cristata) is a pelagic species distributed throughout the North Atlantic Ocean They comprise two stocks; the Northeast and the Northwest Atlantic, breeding off the eastern and western coast of Greenland, respectively [7]. The Northwest Atlantic stock has increased in recent decades and the size was estimated to be 593,500 animals in 2005 [9]. Both hooded seal stocks have been subjected to commercial exploitation since the late seventeenth century [10], ; during the last 25 years, the hooded seal hunt for both stocks has been regulated by quotas. Whether the presence of B. pinnipedialis is affecting the population dynamics of the hooded seal is unknown and increased knowledge about the strains ability to establish persistent infection and cause pathology is warranted
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