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SummaryBackgroundEquine proliferative enteropathy (EPE) is an enteric disease induced by the bacterium Lawsonia intracellularis that causes sporadically or endemically severe enteritis in foals.ObjectivesThe current study aimed to describe the kinetic of serum antibodies against Lawsonia intracellularis by Immuno‐Peroxidase‐Monolayer‐Assay (IPMA) before and after single or double intra‐rectal vaccination of foals with the attenuated live vaccine Enterisol Ileitis® in comparison to non‐vaccinated control foals. Additionally, we evaluated whether seroconversion after vaccination might provide information about the protection against EPE.Study designProspective cohort study.MethodsFive consecutive serum samples were evaluated by IPMA from all 210 foals: group 1 (single vaccination) = 70; group 2 (two vaccinations) = 69; group 3 (control group) = 71. The study period stretched from 2 weeks before to 6 weeks after the first vaccination.ResultsThe analysis showed 944 (89.9%) seronegative samples. 45 samples of group 1 (single vaccination), 56 samples of group 2 (two vaccinations) and five samples of the control group were seropositive during the study period. A total of 63/210 (30%) foals seroconverted during the study period. In foals vaccinated once (n = 70), 32 foals seroconverted, in group 2 (two vaccinations, n = 69) 28 foals seroconverted and in the control foals (n = 71), three foals seroconverted. The vaccinated foals showed significantly more often seroconversion than the control foals (p < 0.0001). After the end of the study period, a total of six foals (two vaccinated foals, and four non‐vaccinated foals) were diagnosed with EPE.Main limitationsA longer study period might have added more information on the humoral response to vaccination.ConclusionsMeasurable Lawsonia intracellularis‐antibodies can be detected after intra‐rectal vaccination, but serological testing the time around the vaccination does not seem to be a reliable method to assess the efficacy of the vaccination.

Equine proliferative enteropathy (EPE) is a well-recognized disease in foals caused by Lawsonia intracellularis. The aim of this study was to analyse clinicopathologic parameters and antibody titres up to the diagnosis of EPE. During the 2019 season, all foals born on a large breeding farm in Germany were enrolled in a monitoring program for EPE from four to nine months of age, including evaluation of rectal temperature, white blood cell count as well as serum total protein and albumin. 42 foals developed EPE between September 2019 and January 2020. Data sets of these foals and 83 age matched control foals were included in this study. All affected foals showed hypoproteinaemia and 39/42 showed hypoalbuminaemia at the onset of EPE. Total protein and albumin decreased rapidly within 7.5 days on average before the diagnosis of EPE. Both total protein and albumin values were significantly lower in the EPE-group compared to the matching foals (p < 0.0001). Seroconversion was observed in all 42 affected foals and in 50/83 matching foals. At the time of diagnosis, affected foals had a significantly higher titre compared to the matching foals (p < 0.0001). Nevertheless, the titre increased significantly between the preceding sampling and the week of diagnosis in both groups (p < 0.0001). Faecal qPCR for Lawsonia intracellularis revealed positive results in 22/42 affected foals. Based on the data analysed here, a high IPMA-titre does neither indicate protection against EPE nor a definite diagnosis of EPE, as both healthy foals and those with clinical EPE show a positive antibody titre against Lawsonia intracellularis.

The objectives of this study were to investigate the kinetics of Lawsonia intracellularis (L. intracellularis) antibodies in foals on a farm with occurrence of equine proliferative enteropathy (EPE) by immunoperoxidase monolayer assay (IPMA). 63 foals were monitored from the age of two to 10 months at two-week intervals via physical examination and selected blood parameters. Serum was used to measure total protein and albumin concentrations as well as antibodies to L. intracellularis by IPMA. In case of hypoproteinaemia and/or hypoalbuminemia, a transabdominal ultrasonographic examination was performed to measure the wall thickness of small intestinal loops. Rectal swabs were taken from foals with suspected EPE to test for L. intracellularis by polymerase chain reaction. 55 of the monitored foals developed antibodies against L. intracellularis, only three foals developed EPE. The progressions of the individual antibody titres showed great variability, no specific pattern was observed. Foals with at least two consecutive seropositive samples considering an interval of two weeks did not develop EPE later during the observation period. Four foals showed developments of antibody titres against L. intracellularis interrupted by one or two negative serum results. Since there was no uniform titre progression and foals with and foals without EPE showed high antibody titres that were detectable for different lengths of time, it was not possible to conclude the further titre progression in foals based on the kinetics. The results illustrated that a single blood analysis is not always reliable to determine by IPMA whether a foal has been infected with L. intracellularis. Due to technical weaknesses of IPMA, the authors recommend to run all samples in duplicate in order to obtain reliable results on the foal's exposure to L. intracellularis for further studies on the kinetics of L. intracellularis antibodies and when using the serology as a diagnostic tool for detecting L. intracellularis.