Farm prevalence studies in many countries throughout Europe, Asia and North America have now indicated that a quarter to one half of pig farms surveyed has had a serious recent problem with Ileitis. Serologic evidence of exposure suggests over 90% of farms in most countries harbour the organism.

The prevalence of infection of pigs within an affected farm is varying from 5 to 7% of growing and finishing pigs during a disease episode (McOrist et al. 2003). Lawsonia intracellularis and the associated disease, proliferative enteropathy, are very common, affecting pigs raised under various management systems around the world: extensive and intensive, single and multiple site.

The organism and the disease have been detected in all regions of all countries where pigs are raised. There is therefore an urgent need to examine the important features of clinical signs, diagnosis, therapy and control now that major advances are taking place in the tools available for investigation (ELISA, PCR).