Lawsonia intracellularis: humoral immune response and fecal shedding in weanling foals following intra-rectal administration of frozen-thawed or lyophilized avirulent live vaccine.

This study explores the immune response and fecal excretion of the bacterium Lawsonia intracellularis in young foals after being given a vaccine via the rectum. The vaccine was administered in two forms: either a frozen-thawed variant or a freeze dried version. The results suggest that both versions of the vaccine are safe and lead to similar outcomes in terms of immune response and fecal excretion of the bacterium.

Introduction to the Research

• The research focuses on investigating the immune response—specifically the humoral immune response, which pertains to antibodies and other proteins circulating in the blood—and the fecal shedding (excretion via dung) of the bacterium Lawsonia intracellularis.
• 20 weanling foals (young horses that have recently been weaned from their mothers) served as the subjects of the study.
• The foals were given a vaccine against Lawsonia intracellularis via the rectum, in hopes that it would stimulate an immune response against the bacteria and help the foals’ bodies to eliminate it.

Administration of the Vaccine

• The vaccine was administered in two different forms—either as a frozen-thawed variant or in a freeze-dried (lyophilized) form.
• Each foal received a dose of 30 mL of the vaccine, with administrations occurring twice, 4 weeks apart.

Measurement and Testing

• Following vaccination, serum samples (the clear liquid that can be separated from clotted blood) were taken from each foal every four weeks for a total of 16 weeks.
• These samples were then tested for anti-Lawsonia intracellularis specific IgG—a type of antibody—using a procedure known as immunoperoxidase monolayer assay. This would reveal whether the foals were mounting an immune response against the bacteria.
• In addition to this, rectal swabs were collected from each foal every other day for a period of 4 weeks after the vaccination. These samples were tested for the presence of the Lawsonia intracellularis bacteria using real-time PCR, an advanced laboratory technique for DNA amplification and detection.

Findings of the Research

• The data gathered and observed from the study suggests that regardless of the form of the vaccine—whether it was freeze-thawed or lyophilized—the results were comparable.
• In both cases, the onset and duration of fecal shedding of the bacteria and the presence of specific antibodies in the bloodstream were similar.
• Furthermore, both vaccine formulations were found to be safe when administered intra-rectally in weanling foals, suggesting potential for practical application.