Prevalence of Brachyspira hyodysenteriae and Brachyspira pilosicoli isolated in Spanish pig farms from 2011 to 2015

Brachyspira hyodysenteriae is the aetiologic agent of swine dysentery (SD), an infectious disease that affects growing and fattening pigs causing severe bloody diarrhoea and haemorrhagic colitis. Brachyspira pilosicoli causes a non-fatal and non-bloody milder catarrhal colitis named porcine intestinal spirochaetosis (PIS) in young pigs.

Our purpose has been to determine the prevalence of these two spirochaetes in Spanish farms with diarrhoea and clinical signs of SD during the 2011- 2015 period.

Farms and samples: During 2011, a total of 1846 faecal samples were recovered from 203 farms; 1403 samples belonging to 164 farms were analysed in 2012; the following year, 871 faecal samples were tested from 116 pig farms; during 2014, 858 samples were collected from 117 farms; and finally, a total of 647 pig faeces samples were evaluated from 88 farms in 2015. The farms were distributed through all the Spanish territory.

Microbiological and molecular diagnosis: All the samples were streaked onto CVS (colistin, vancomicin, spectinomicin) selective agar plates. The strains were isolated from those agar plates showing haemolytic activity and with spirochaetes visible under the microscope. The DNA of these strains was extracted and used as template for PCR detection of the putative haemolysin regulatory gene tlyA of B. hyodysenteriae and the 16S rDNA gene of B. pilosicoli.

In 2011, 95 farms were found to be positive to B. hyodysenteriae (46.80%). This percentage was lower, 39.02%, in 2012, with a prevalence of 64 positive farms. During 2013, the value increased until 44.83% (52 positive pig farms) and it remained stable in 2014, with 44 farms in which it was possible to detect the bacteria (44.44%). Finally, it has been possible to observe a decrease of the prevalence during 2015, with 31 positive farms, a 35.23%.

Otherwise, during this period, the prevalence of B. pilosicoli has ranged between 1.22 and 2.56%, not being detected any case in 2013 and 2015. None of the farms was positive to the both pathogenic strains.

Although there are several factors that can affect the appearance of B. hyodysenteriae infections such as the management, the housing or the diet, our results indicate that SD is present in a 35.23-46.80% of the studied farms with diarrhoea in adult pigs and clinical suspicion of swine dysentery in Spain. Moreover, the trend to a lower antimicrobial susceptibility among B. hyodysenteriae isolates could complicate the control of this infection in swine farms. Conversely, the low incidence of B. pilosicoli suggests that PIS plays a minor role in digestive processes in pigs of the Spanish farms analyzed in this study.

Disclosure of Interest: None Declared