Occurrence of a monophasic strain of Salmonella group B isolated from cetaceans in England and Wales between 1990 and 2002.

Between September 1990 and December 2002, 511 cetacean carcasses stranded or caught in commercial fisheries in England and Wales were examined post mortem. Salmonella group B was isolated from 60 of 279 (21.51%) harbour porpoises (Phocoena phocoena), predominantly from lung tissue. Forty-three of the Salmonella group B isolates were subsequently serotyped and all found to have the antigenic structure O4,12:a:-. The annual proportion of harbour porpoises testing positive for Salmonella O4,12:a:- increased significantly from 6% in the early 1990s to 27% after 1999. The cause(s) of the increasing prevalence of Salmonella O4,12:a:- are not known, but may reflect natural variation in the epidemiological cycle of Salmonella O4,12:a:- in harbour porpoises. The probability of isolating Salmonella O4,12:a:- from harbour porpoises increased with age, suggesting that the mode of transmission is principally horizontal. There appeared to be a weak degree of seasonality in the probability of isolating Salmonella O4,12:a:- with a low proportion of cases in the months of April and May. Based on pathological findings from infected carcasses, Salmonella O4,12:a:- may be part of the normal commensal flora of the lungs of cetaceans with the potential to act as an opportunistic pathogen.