Serological responses of Australian horses using a commercial duplex indirect ELISA following vaccination against strangles.

This research study evaluates the effectiveness of a commercial vaccine in protecting Australian horses from a bacterial infection called strangles. The results, based on performances of 19 horses, suggest that this vaccine is unlikely to interfere much with the ability to detect the disease and may thus serve as a useful tool in controlling strangles outbreaks in this population.

Research Method

• The researchers administered a primary course of Streptococcus equi subsp. equi (S. equi) extract vaccine to a sample of 19 horses owned by clients from five different properties.
• The immune response of these horses to the vaccine was measured using a duplex indirect ELISA (iELISA), a laboratory test that can detect antibodies produced by the immune system in response to antigens, which in this case were fragments of two specific proteins found on the cell wall of the S. equi bacteria.
• Blood samples were taken from the horses at various time points surrounding the vaccination process, including immediately before each of the three vaccinations, and again 28 and 56 days after the third vaccination.

Findings

• The results showed that significant increases in mean antibody levels among horses being vaccinated were only observed in response to one of the two antigens tested; AgC, implying the immune response was specific.
• There was no substantial increase in the average quantity of antibodies in response to the other antigen, AgA, highlighting the importance of the specificity of immune responses.
• Only a minority, specifically 22% of the horses, exceeded the test cut-off for antigen C, indicating the majority of horses were unlikely to respond to this antigen.

Conclusion

• The researchers concluded that vaccination of Australian horses is unlikely to interfere significantly with the detection of strangles using the duplex iELISA.
• They also discovered that most horses did not respond to AgC, which suggests that the vaccine was only effective for a small percentage of horses.
• Based on these findings, they suggested that the results of this study validate the usefulness of the duplex iELISA to assist control measures for strangles outbreaks in Australian horse populations.