Single and double vaccination against Lawsonia intracellularis in foals: Investigation of the humoral immune response following different vaccination protocols

Summary Background Equine proliferative enteropathy (EPE) is an enteric disease induced by the bacterium Lawsonia intracellularis that causes sporadically or endemically severe enteritis in foals. Objectives The 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 design Prospective cohort study. Methods Five 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. Results The 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 limitations A longer study period might have added more information on the humoral response to vaccination. Conclusions Measurable 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.