Use of a virulence-associated protein based enzyme-linked immunosorbent assay for Rhodococcus equi serology in horses.

The research article focuses on the development of an enzyme-linked immunosorbent assay (ELISA) against Rhodococcus equi in horses and its utility in tracking the course of the infection or the immunization response to a virulence-associated protein (VapA) based antigen.

Methodology

• The study team developed an ELISA against Rhodococcus equi, a bacteria that is often problematic in horse breeding operations, causing pneumonia in foals.
• They extracted the whole cell material from the bacteria, with a focus on the virulence associated protein (VapA). Triton X-114 detergent was used for the extraction process.
• The study shows that there was a clear correlation between the ELISA titres (a measure of antibodies in blood) and the antibodies reacting with VapA on Western blots (a technique in molecular biology used to detect specific proteins in a sample).

Findings

• The testing indicated significant variation in antibody titres of non-immunized mares and undetermined timelines for when the colostrally derived antibody (antibodies transferred through colostrum i.e., first milk after birth) in foals declined.
• The foals typically saw a decrease in the antibodies to their lowest levels at 4-8 weeks of age. Seroconversion (the time period during which a specific antibody develops and becomes detectable in the blood) in foals happened around 8-10 weeks of age, influenced by the maternal titre and the birth month of the foal.
• The researchers observed more marked seroconversion in foals born in late summer, suggesting an effect of seasonal change on the immune response.

Immunisation Response

• When used to monitor the response to immunisation with the same extracted material, the ELISA revealed that the immunised mares before parturition developed high antibody titres, which were then transferred to their foals through colostrum.
• The foals that were born to these mares and subsequently immunised with the antigen showed a significant response to the antigen after birth.
• A non-vaccinated control group of foals seroconverted at an age of 6-8 weeks, which is in line with the natural infection course observed in the initial study samples.
• The results support the use of the VapA-based ELISA for tracking the progression of natural infections with Rhodococcus equi as well as immunisation responses to the VapA-based antigen.