Lack of correlation between antibody titers to fibrinogen-binding protein of Streptococcus equi and persistent carriers of strangles.

This study examines whether there is a correlation between antibody responses to a certain protein in the bacteria “Streptococcus equi” and the persistence of the animal disease strangles. The paper ultimately finds that while their proposed method of detection could confirm a recent exposure to the bacteria, it could not accurately predict if the infection would persist.

Research Background

• The research was prompted by a lack of studies that use an indirect enzyme-linked immunosorbent assay (iELISA) in monitoring outbreaks of strangles, a disease in horses caused by Streptococcus equi.
• Prior to this research, there had been propositions to use serologic responses (reactions of the immune system that can be measured in the blood) to identify ongoing carriers of this bacterium, but no scientific evaluation had tested this theory.

Methodology

• The specific aims of the study were to understand the duration and level of specific antibody production in ponies following a natural strangles outbreak, and to assess if results from the serologic test could predict persistent carrier status.
• Samples were taken before and after a natural strangles outbreak, and those who continued to carry S. equi were identified through culture and polymerase chain reaction (PCR) testing from fluid collected in certain areas of the nose and throat, both after recovery and postmortem.
• Logistic regression analysis was used to identify if there was a correlation between the serologic response and the status of the bacterium’s persistence.

Findings

• The serologic responses measured by the ELISA could definitively confirm recent exposure to S. equi.
• However, this immune response could not predict the persistence of the carrier status in the outbreak of strangles.

Implications

• In light of these findings, the authors of the study conclude that the most accurate method for identifying ongoing carriers of S. equi remains the classic approach: utilizing a guttural pouch endoscopy and subsequent culture or PCR testing.