Brief report Occurrence of a monophasic strain of Salmonella group B isolated from cetaceans in England and Wales between 1990 and 2002 Carlos A. Valderrama Vasquez, 1,2 * Shaheed K. Macgregor, 1 J. Marcus Rowcliffe 1 and Paul D. Jepson 1 1 Institute of Zoology, Zoological Society of London, Regent’s Park, London NW1 4RY, UK. 2 Fundación Vida Silvestre Neotropical, Carrera 65b no. 10 a -05, Bogotá DC, Colombia. Summary Between September 1990 and December 2002, 511 cetacean carcasses stranded or caught in commer- cial fisheries in England and Wales were examined post mortem. Salmonella group B was isolated from 60 of 279 (21.51%) harbour porpoises (Phocoena pho- coena), predominantly from lung tissue. Forty-three of the Salmonella group B isolates were subsequently serotyped and all found to have the antigenic struc- ture 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 preva- lence 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, suggest- ing 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 ceta- ceans with the potential to act as an opportunistic pathogen. Introduction The genus Salmonella is a well-recognized pathogen of people, livestock, wild animals, birds, reptiles and even insects. Microscopically, Salmonella spp. are small, straight, Gram-negative rods (0.7–1.5 ¥ 2.0–5.0 mm). Most are motile but non-motile forms also occur (Williams and Barker, 2001). Bacterial diseases are a significant cause of death in marine mammals, either as a primary cause or secondary to viral or helminth infections (Moeller., 1997; Dunn et al., 2001). In cetaceans, Salmonella spp. bacteria are common pathogens and may cause severe necrotizing enteritis and/or septicaemia in affected animals (Kirkwood et al., 1997; Moeller, 1997; Jepson et al., 2000; Tryland, 2000; Jepson, 2005). Clinically, animals have been reported to show severe enteritis with necrosis and/or haemorrhage and septicaemic cases usually die without showing clinical signs. In some cases, septicaemia can lead to complications such as bronchopneumonia, necrotizing hepatitis, meningoencephalitis and abscessation (Moeller, 1997). Isolates of Salmonella spp. have been reported from killer whales (Orcinus orca), bottlenose dol- phins (Tursiops truncatus) and pilot whales (Globicephala melas) (Tryland, 2000), and Salmonella DT12 has been reported from a harbour porpoise (Foster et al., 1999). Furthermore, there have been reports of large outbreaks of salmonellosis in humans who have eaten whale meat or blubber, with clinical signs including fever, chills, nausea, vomiting, cramps and diarrhoea (Tryland, 2000). Although the primary site of infection of Salmonella spp. is the gastrointestinal tract (Williams and Barker, 2001), a monophasic group B Salmonella with the antigenic struc- ture O4,12:a:- has been isolated from harbour porpoises (Phocoena phocoena) where the lung is the tissue most frequently infected (Foster et al., 1999). It has been sug- gested that this particular serotype of Salmonella is host- adapted and opportunistic because it has been isolated from pneumonic and non-pneumonic lungs, including from the lungs of healthy harbour porpoises that were accidentally caught in fishing nets or killed by bottlenose Received 25 April, 2007; accepted 9 March, 2008. *For correspondence. E-mail carlos.valderrama@fvsn.org; Tel. (+57) 3114668425; Fax (+57) 12611942. Environmental Microbiology (2008) 10(9), 2462–2468 doi:10.1111/j.1462-2920.2008.01651.x © 2008 The Authors Journal compilation © 2008 Society for Applied Microbiology and Blackwell Publishing Ltd