The effect of passively acquired antibodies onLawsonia intracellularisinfection and immunity in the horse

Abstract

This is the first study to show that passively acquired antibodies to L. intracellularis do not have an effect on the occurrence of clinical or subclinical EPE. A number of novel findings, including identification of the disease rate among naturally exposed horses, warrant additional work as they may help to identify potential risk factors for L. intracellularis exposure and/or the reservoir host(s) of the bacterium.

The Possible Role Mares Play in the Epidemiology of Equine Proliferative Enteropathy

“…Although most young horses being weaned by this point could account for this difference, the possibility that mares previously transmitted the bacterium to the foals cannot be ruled out. It should be noted that passively acquired antibodies to L. intracellularis were detected immediately after birth in some foals from both farms but were below the ELISA cutoff for a positive result after the second month of age [11].…”

“…Based on experimental challenge studies in horses, a 14-to 21-day incubation period has been proposed for EPE as seropositive titers are typically detected approximately 14 days after challenge [3,19]. However, as recently documented [11], the rate of naturally occurring EPE cases (clinical and subclinical) among exposed horses is significantly lower (approximately 11% vs. 33%-66%) than that seen with experimental EPE models [3,19,20]. This difference likely reflects the large challenge doses that are used to induce clinical disease in experimental settings.…”

“…The procedures used for this project are similar to those that have been reported previously [11]. Briefly, within 48 hours of parturition, whole blood samples were collected from the mare and newborn foal.…”

“…Serologic status in regards to L. intracellularis was determined using the ELISA method, as previously described [11,12]. A logarithmic regression line from a standard curve of a known immunoperoxidase monolayer assay (IPMA) titer sample was generated on each plate to allow for the conversion of tested sera to ELISA units (EU).…”

“…At the end of the study, foals were placed into four categories based on their L. intracellularis and/or EPE status from October to February, as previously described [11]: presumptive clinical EPE, presumptive subclinical EPE, seropositive only, or seronegative. Given that definitive diagnosis of EPE can only be made at necropsy, all diagnoses of EPE were considered presumptive.…”