Epidemiological investigations on Lawsonia intracellularis infections in pig herds

Objective: A serological screening study was carried out to determine the prevalence of Lawsonia (L.) intracellularis infections in German pig herds. Additionally a cross-sectional study of eight farrow-to-finish herds which was designed to investigate the dynamics of seroconversion. In addition, bacteriological tests were carried out on faec-al and intestinal samples from herds with diarrhoea problems to compare the prevalence of L. intracellularis with that of Brachyspira spp., Salmonella spp. and Escherichia (E.) coli. Material and methods: An indirect immunofluorescence technique was used to test blood samples from the herd screening study (n = 7546 from 694 herds) and the cross-sectional study (n = 936 from 8 herds) for antibodies to L. intracellularis and to detect L. intracellularis in the faecal and intestinal samples (n = 826 from 403 herds). The faecal and intestinal samples were tested for Brachyspira spp., Salmonella spp. and E. coli using culture techniques. Results: Antibodies to L. intracellularis were detected in 43.2% of the blood samples tested and in 81.3% of the herds tested. Herds with gilts and sows and fattener-only herds had a higher incidence of seropositivity than piglet-rearing herds, irrespective of whether the piglets were fattened on site or not. The incidence of seropositivity in herds with clinical symptoms of porcine proliferative enteropathy (PPE) was similar to that in herds free from clinical disease or with clinical symptoms of other diseases. The cross-sectional study showed that seroconversion occurred in some animals as early as 10 weeks but that most animals seroconverted between 13 and 16 weeks. Bacteriological testing of faecal and intestinal samples demonstrated that, in herds with diarrhoea problems, haemolytic E. coli and L. intracellularis were much more common (occurring in 48.4% and 33.7% of herds) than Brachyspira (B.) hyodysenteriae (21.1%), Salmonella spp. (17.3%) and B. pilosicoli (2.5%). Mixed infections of L. intracellularis with B. hyodysenteriae, B. pilosicoli or Salmonella spp. were rare, occurring in 3.5%, 1.0% and 5.6% of herds respectively. Conclusions and clinical relevance: The results indicate that infection with L. intracellularis is very widespread in Germany and that it occurs both in herds with diarrhoea and unthriftiness problems and in herds without clinical symptoms. Specific diagnostic measures are therefore required to exclude other diarrhoeal pathogens.