Héctor Argüello Rodríguez

Prevalence of Brachyspira species in pigs with diarrhoea in Spain

PATHOGENIC Brachyspira species (formerly Serpulina species [Ochiai and others 1997]) associated with spirochaetal colitis of pigs include Brachyspira hyodysenteriae, the cause of swine dysentery, and Brachyspira pilosicoli, the cause of porcine colonic or intestinal spirochaetosis (Duhamel 2001). Recent changes in the management of pigs in different parts of the world, including Spain, have resulted in a shift in the relative prevalence of pathogenic Brachyspira species. While the prevalence of swine dysentery has decreased dramatically among commercial pig production units in the USA, restricted administration of antimicrobial agents used to promote growth and feeding efficiency, may have contributed to the reemergence of spirochaetal colitis in the EU (Laval 2002). Despite the known impact of Brachyspira-induced spirochaetal colitis on the efficiency of pig production, and the recent implementation of restrictions on the use of antibiotic growth promoters, the prevalence of pathogenic Brachyspira species on commercial pig farms in Spain is currently unknown. The purpose of this study was to determine the relative prevalence of B hyodysenteriae and B pilosicoli on those commercial pig farms in Spain that had clinical signs of diarrhoea among the animals. Between October 2000 and December 2003, a total of 3849 faecal samples were obtained from 421 commercial pig farms with a history of diarrhoea among the growers, finishers or sows. On each farm, five to 20 faecal swabs were taken directly from the rectums of pigs with clinical signs of diarrhoea or decreased growth rate. The swabs were placed in Amies transport medium and shipped on ice by overnight courier to the laboratory. Each specimen was cultured anaerobically using colistin, vancomycin and spectinomycin selective agar medium, and pathogenic Brachyspira spirochaetes were identified directly from primary cultures using B hyodysenteriae(Leser and others 1997) and B pilosicoli(Muniappa and others 1997) specific PCR assays (Barcellos and others 2000, De Arriba and others 2002). A farm was considered positive when pathogenic Brachyspira spirochaetes were found in at least one faecal sample. At least one pathogenic Brachyspira species was found on 34·9 per cent of the farms. The prevalence of pathogenic Brachyspira species among farms and faecal samples are presented in Table 1. The mean within-farm percentage for positive faecal samples was 50·2 for B hyodysenteriae and 23·9 for B pilosicoli. Ten farms and 12 samples were positive for both pathogenic Brachyspira species. The mean within-farm percentage for positive samples for B hyodysenteriae and B pilosicoli on these farms was 48·1 and 24·3 per cent, respectively. The 32·1 per cent farm prevalence of B hyodysenteriae in the present survey was similar to the 35·3 per cent reported previously among 17 commercial pig farms in Brazil on which the unmedicated pigs had clinical signs of diarrhoea (Barcellos and others 2000). In contrast, lower rates of prevalence of B hyodysenteriae, ranging between 2·5 and 28·4 per cent, have been reported in surveys conducted on commercial pig farms in other European countries (Møller and others 1998, Thomson and others 1998, Stege and others 2000, Thomson and others 2001, Magistrali and others 2002). The 5·2 per cent prevalence for B pilosicoli on farms was lower than previous surveys conducted in the Republic of Korea (Choi and others 2002), Finland (Heinonen and others 2000), Denmark (Stege and others 2000), Sweden (Fellström and others 1996), and the UK (Thomson and others 1998, 2001). However, the 23·9 mean within-farm percentage for positive faecal samples for B pilosicoli was within the range of 5·0 to 75·0 per cent reported by Stege and others (2000). The present survey began approximately one year after the restrictions on the use of antibiotic growth promoters were fully implemented in Spain. Although the administration of antimicrobial agents effective against pathogenic Brachyspira species might affect the relative rates of prevalence in this study, the structure and management of pig production, as well as the sampling protocols and laboratory detection methods in different countries, are likely to account for the variable results seen in different surveys. The percentages of farms positive for pathogenic Brachyspira species were compared between each year of the survey, and according to the age of the pigs with clinical signs of diarrhoea, using chi-squared analysis (SPSS 11.01; Microsoft). Because of the small number of farms examined in 2000, only data obtained from 2001 to 2003 were included in the analysis (Table 2). Although there was no significant difference in the farm prevalence of B hyodysenteriae relative to B pilosicoli for each individual year, the prevalence of B pilosicoli on farms doubled from 2·2 to 5·3 per cent, while the prevalence of B hyodysenteriae concurrently decreased by 11·9 per cent over the three-year study period. These observations suggest a shift in the relative prevalence of the agents responsible for spirochaetal colitis after the ban on antibiotic growth promoters in Spain, implemented as part of the effort to control swine dysentery in the Spanish pig industry. A total of 332 farms were able to provide information on the ages of the pigs with clinical signs of diarrhoea. Diarrhoea affecting grower pigs (five to 12 weeks of age) was reported on 12·0 per cent of the farms, whereas diarrhoea affecting finisher pigs (12 weeks of age to market) or sows was reported on 48·2 per cent and 45·8 per cent of the farms, respectively. More than one age category of pig had diarrhoea on 6·3 per cent (21) of the farms, and on one farm, pigs in all age categories had diarrhoea. B hyodysenteriae was found on 28·9, 33·7 and 22·5 per cent of the farms on which diarrhoea affected sows, finishers and growers, respectively. B pilosicoli was found on 2·6, 5·6 and 12·5 per cent of the farms on which diarrhoea was observed among sows, finishers and growers, respectively. There was no significant difference in the prevalence of B hyodysenteriae according to the age of the pigs with diarrhoea. In contrast, B pilosicoli was more frequently found on farms on which grower pigs had diarrhoea (χ2=4·87, P<0·05). This observation is consistent with previous reports indicating that grower pigs are most susceptible to porcine colonic spirochaetosis (Duhamel 2001). Although regional differences might account for the lower prevalence of B pilosicoli in Spain, since only 12·0 per cent of the farms reported diarrhoea affecting grower pigs, Number positive (%) Brachyspira species Farms Faecal samples