Serial use of serologic assays and fecal PCR assays to aid in identification of subclinical Lawsonia intracellularis infection for targeted treatment of Thoroughbred foals and weanlings.

The research study aimed to evaluate the effectiveness of using a combination of immunoperoxidase monolayer assays (IPMAs) and fecal polymerase chain reaction (PCR) tests, in conjunction with other diagnostic methods, in detecting subclinical Lawsonia intracellularis infections in Thoroughbred foals and weanlings.

Research Methodology

• The study involved 100 foals and weanlings – 53 from a farm where L. intracellularis infection was endemic and 47 from a non-endemic farm.
• Every four weeks, serum from each participant was collected and tested for antibodies to L. intracellularis using an IPMA test.
• Bi-weekly fecal samples were collected and subjected to an L. intracellularis-specific PCR test.
• If either IPMA or PCR tests showed positive results or if the subjects showed clinical signs consistent with equine proliferative enteropathy (EPE), further clinicopathologic testing was performed to decide the treatment plan.

Research Findings

• None of the foals tested positive for the L. intracellularis-specific IPMA test before weaning.
• 60.4% of the weanlings at the endemic farm and 17% at the non-endemic farm tested positive using the IPMA test.
• Only 6 weanlings at the endemic farm tested positive via the fecal PCR test while none at the non-endemic farm did.
• Out of the 32 weanlings with positive IPMA results at the endemic farm, 19 were treated for EPE, of which five exhibited clinical signs of EPE. No weanlings at the non-endemic farm showed clinical signs or were treated for EPE.

Conclusions

• The results suggested that IPMA tests could be a useful tool for identifying weanlings exposed to L. intracellularis especially in endemic areas.
• However, the validity and utility of the fecal PCR tests seemed more questionable given the lower rate of positive results.
• More research is needed to improve understanding of the infection dynamics of L. intracellularis in horse populations, and to develop more sensitive and reliable diagnostic tools.