Preliminary evaluation of a dual antigen ELISA to distinguish vaccinated from Leptospira infected horses.

This research article discusses the development and preliminary evaluation of a dual antigen ELISA – a laboratory test – to differentiate between horses that have been vaccinated for Leptospira and those that are infected with the bacteria. The paper outlines how the test is based on specific proteins produced in response to the bacteria and the differences in antibody response seen in infected versus vaccinated horses.

Objective of the Study

• The fundamental objective of the study was to develop an enzyme-linked immunosorbent assay (ELISA) that is capable of distinguishing between horses that are vaccinated for Leptospira interrogans and those that have been naturally infected with the bacteria.

The Role of Leptospira Proteins

• The paper outlines how various proteins of the Leptospira interrogans bacteria – specifically the sph1, ligA, hsp15, and LipL45 – are significantly increased in horses that are infected, but are barely or not at all detectable in cultivated organisms.
• On the contrary, the protein LipL32 can be found abundantly in cultivated Leptospira, and also triggers antibody responses to infection.

Development of the ELISA

• The researchers developed an ELISA based on the LipL32 or Leptospira sonicate (a preparation created by disrupting the bacteria), and host-induced proteins to differentiate between serum antibody resulting from vaccination and from natural infection.
• The researchers examined the immunoglobulin G (IgG) – a type of antibody – specific for the various recombinant proteins, in the serum of horses naturally infected with Leptospira and those immunised with the serovar Pomona bacterin (a type of vaccine).

Findings and Conclusion

• The study found that sera from infected horses reacted strongly with the proteins Sph1, LigA and Lk90, but not the sera from vaccinated ones. Similarly, the proteins LipL45 and Hsp15 showed moderate reactions with infection sera but weak reactions with the vaccine sera.
• Both infected and vaccinated horses showed a strong reaction to Leptospira sonicate and LipL32.
• As anticipated, the vaccine produced from culture was unable to stimulate an antibody response to host-induced proteins.
• Based on these findings, the researchers concluded that a dual antigen ELISA built on Leptospira sonicate or LipL32 combined with host-induced Sph1 and Lk90 could be a useful tool in distinguishing between responses due to vaccination and natural infection.