Epidemiological investigations on Lawsonia intracellularis infections in pig herds

Objective: Investigation of the prevalence of Lawsonia (L.) intracellularis infections in Germany by serological herd screening. Additionally, in eight farrow-to-finish herds a cross sectional study was carried out to determine the course of seroconversion. Faecal and intestinal samples were examined to compare the prevalence of L. intracellularis and Brachyspira spp., Salmonella ssp. as well as Escherichia (E) coli. Material and methods: An indirect immunofluorescence technique (IFAT) was used to analyse blood samples (screening: n = 7546 from 694 herds, cross sectional study: n = 936 from eight herds) for the presence of antibodies against L. intracellularis. Faecal and intestinal samples were tested for the presence of L. intracellularis by IFAT and for Brachypira spp., Salmonella spp. as well as E. coli by culture techniques. Results: Antibodies against L. intracellularis could be detected in 43.2% of the blood sanmples and in 81.3% of the investigated herds. Sow herds and fattening herds were more often seropositive than piglet herds with or without fattening units. Frequent seropositive results were demonstrated in herds with typical signs (diarrhea and/or wasting) of porcine proliferative enteropathy (PPE) as well as in herds with other clinical symptoms or without any clinical signs. The cross-sectional study showed first antibodies in pigs between week six and 10 before main seroconversion developed between week 13 and 16. Bacteriological investigation of faecal and intestinal samples of diarrheic pigs showed highest rates for haemolytic E.coli(48.4%) and L. intracellularis (33.7%) followed by B. hyodysenteriae (21.1%), Salmonella spp. (17.7%) and B.pilosicoli(2.5%). Mixed infections of animals shedding L.intracellularis were rarely found for B. hyodysenteriae (3.5%) or Salmonella spp. (5.6%). Conclusions and clinical relevance: Results indicate a high prevalence of L. intracellularis infections in pig herds all over Germany. Because L. intracellularis infections also were detected frequently in herds without clinical signs of PPE, specific diagnostic measurements are necessary in diarrheic herds to exclude other reasons for disease.