High prevalences of anti-Brucella antibodies have been reported in hooded seals (Cystophora cristata - HS), suggesting that brucellosis (a bacterial infection inducing abortion in terrestrial mammals) may contribute to the dramatic decline of the Northeast Atlantic stock. However, pathological changes have never been identified in infected HS. Age-dependent serological and bacteriological patterns suggest that seals are exposed to an environmental source of B. pinnipedialis during their first year of life (after weaning), followed by the clearance of infection. This raises questions about the existence of a reservoir of B. pinnipedialis in the HS food web.
Atlantic cod (Gadus morhua) is part of the diet of adult HS, and was, therefore, experimentally infected with a B. pinnipedialis HS wildtype strain. Fish were challenged with 108B. pinnipedialis intraperitonally. No mortality or macroscopic pathology was recorded. Samples of blood, liver, spleen, muscle, heart, head kidney, female gonads were collected from 5 fish at day 1, 7, 14 and 28 pi to determine the bacterial load. Brucella pinnipedialis HS strain was retrieved from all organs investigated, except muscle. Our results show that B. pinnipedialis induce bacteremia in 6/8 Atlantic cod for an extended period of time (up to 28 days pi).
Anti-Brucella antibodies were detected in fish at day 28 pi by RBPT and ELISA.
Primary leukocytes were isolated from head kidneys of non-infected fish and challenged with B. pinnipedialis (reference strain) or the HS strain used in vivo. Both strains entered the leukocytes and survived intracellularly without any reduction in retrievable numbers of bacteria for at least 48 hours.
Our results indicate that B. pinnipedialis has a prolonged course of infection in Atlantic cod. Atlantic cod may thus act as a transmission host for B. pinnipedialis in the marine environment.