Risk factors associated with Lawsonia intracellularis in English pig farms.

Porcine proliferative enteropathy (PPE) caused by the bacterium Lawsonia intracellularis causes considerable economic loss to the pig industry. The objective of this study was to evaluate the seroprevalence of L. intracellularis exposure in different age groups of pigs (growers to finishers) within English farms and to identify potential risk factors. Samples were obtained in a cross-sectional study of 147 farms between 2008 and 2009. Twelve samples (six growers and six finishers) from each farm were tested for L. intracellularis by antibody ELISA. At animal level there was a significant positive linear trend between seroprevalence and age in weeks (r(2)=2.65, P<0.001), with seroprevalence lowest (24.73%) at 11 weeks and highest (93.33%) at 24 weeks. At farm level, seroprevalence was significantly lower in growers than finishers (56.80% vs. 94.26%, P<0.001). Farms reporting minor Salmonella problems and those that brought boars onto the farm had higher odds of testing positive in growers (OR 5.69 and 4.31, respectively. On the other hand, farms where producers considered temperature as an important stress factor (OR=0.3) and which had more than two sites on which pigs are kept (OR=0.16) were less likely to test positive in growers. The current study confirmed the high prevalence of L. intracellularis in English pig farms. The potential risk factors and further information of the disease impact on the farm productivity will aid the development of appropriate control strategies through better understanding of the disease.