younger, susceptible pigs. A more extensive, two-part investigation of the epidemiological aspects of PPE in the field followed. The investigation comprised a farm sampling study and a questionnaire postal survey. In the farm sampling study, faeces samples were collected serially over a ten month period from breeding gilts and their litters. Samples were subjected to PCR for the detection of infection, allowing estimation of within-herd prevalence, as well as determination of possible transmission patterns. The assay successfully detected the presence of L. intracellularis in the weaners and/or growers of three of the five farms selected for this study. The within-herd prevalence for these age-groups ranged from 10 to 30%. The PCR also confirmed infection in several of the adult breeding boars and gilts. The relative expense of the PCR assay dictates that its practical application, at least for the purposes of research, must be targeted. Thus, the sampling study was coupled with a postal questionnaire survey. Mailing questionnaires to almost 600 commercial production units achieved a 56% response rate. This provided a sufficiently large number of herds to allow statistical analysis of possible risk factors involved in the epidemiology of PPE. This survey indicated that the 1993 to 1995 period-prevalence of PPE in the UK was 31%. Based on the number of sows, herd size was an important risk factor, even when herds with under 50 sows were excluded (p<0.005). There was an important link between the occurrence of PE and nucleus herds, with five out of six nucleus herds in the study having had PE diagnosed in the previous three years. This link was strengthened in that herds obtaining replacement breeding boars from nucleus stock were at an increased risk of PE (p<0.05). Factors which could affect the exposure of animals to the faecally-contaminated environment were also significant. Surprisingly, slatted or meshed floors were linked to PE, especially in the younger age-groups (p<0.05). Batch movement of pigs on a house basis was significantly protective against PE (p<0.05), but batch movement on a pen basis only was neither a protective nor a risk factor.

A polymerase chain reaction (PCR) assay was adapted and optimised for specific detection of Lawsonia intracellularis genomic DNA segment in swine faeces. Lawsonia intracellularis is the aetiological agent of porcine proliferative enteropathy (PPE) and the PCR represents the first diagnostic test suitable for ante-mortem use in affected swine. Various methods designed to extract bacterial DNA from faeces were evaluated to establish a convenient and optimum protocol. The PCR was utilised in pig challenge studies to investigate the excretion patterns of L. intracellularis in weaner pigs orally inoculated with pure cultures of L. intracellularis. This challenge work demonstrated that the PCR was a suitable tool for detection of infection, and indicated that individual animals could excrete L. intracellularis organisms for periods of up to ten weeks post-challenge. Such an excretion period has major implications for the transmission of organisms in the field. For example, if infected growers are still shedding L. intracellularis organisms upon entry to the breeding population, then this is a possible route for the transmission of disease to younger, susceptible pigs.

Epidemiology of PPE is complex, but the PCR has proved to be a valuable tool, capable of screening for the presence of L. intracellulars in field conditions. Additionally, its use has permitted some initial conclusions to be drawn regarding the excretion and transmission patterns of this unique organism.