2.1.2 Are there farms completely negative for L. intracellularis?

The clear answer to the question above is “Yes”, but such farms are very rare. Within the 342 farms only 4 farms (1.2%) were negative in all screened age groups. One of these is a closed specific pathogen free (SPF) farm. The others are multi site production systems with geographi­cally separated sow-, nursery- and fattening-farms. In all three farms the sow site was positive while the nursery site as well as one or more of the fattening sites were tested seronegative. The surprisingly low percentage of completely negative farms shows that sanitary and hygienic measures can contribute to lower the risk of infection with L. intracellularis but they can not prevent a herd from getting infected (Stege et al. 2001).