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In the 21st century, the use of antibiotics in the intensive pig production has become much more restricted. This has increased the importance of monitoring programmes and vaccination against infectious diseases.

In our study we surveyed the prevalence of Lawsonia intracellularis in 44 large Hungarian swine herds between July 2019 and May 2022, by using 3 different test methods. A total of 2567 samples were collected, of which 1713 were serological samples. During the slaughterhouse examination, 660 ileal tracts were examined, from which not only the positivity of samples but also the extent of infection was determined. Slaughterhouse checks were performed by using a 0-3 scale scoring system to assess the level of infection in the ileum, which has the disadvantage that it can only be performed post mortem, but a comprehensive picture of the level of infection can be obtained immediately at a low material cost. In addition, 194 faecal samples were taken and tested by qPCR. All three test methods were used parallelly in 6 farms.

97.7% of the surveyed farms were proved to be Lawsonia intracellularis positive, which means that there was only 1 (!) swine farm where the pathogen was not detected. 71% of the serological and slaughterhouse samples were positive. Lower prevalence values were obtained for faecal samples, with 56% of samples showing positivity. In the slaughterhouse tests, a 0-3 scale scoring system was used to assess the level of infection in the ileum. 28.8% of the examined ileums belonged to Category 0 which can be regarded as a negative sample. 44.5% of the samples were in Category 1, showing only minor proliferative lesions in the ileum. A further 26.4% of intestinal samples were classified as Category 2 and 0.3% as Category 3. An average of 2.29 10Log Copies/µl was detected in the tested faecal samples. No quantitative results were obtained for 14% of faecal samples.

The survey results show that the Hungarian swine herds had much higher Lawsonia intracellularis prevalence than the Western European ones, and the control of the infection would be important. The presented test methods, particularly the newly introduced cost-effective slaughterhouse test method, can help to rapidly assess the extent of infection and to monitor the effectiveness of vaccination against Lawsonia intracellularis.