Association of Borrelia burgdorferi with nuchal bursitis and elevated outer surface protein A-specific serum antibodies in horses of the northeastern United States.

OBJECTIVE

Evaluate the incidence of Borrelia burgdorferi in cases of equine nuchal bursitis (NB) and investigate the relationship between elevated serum outer surface protein A (OspA) antibodies and the molecular identification of B burgdorferi in bursal tissue or synovial fluid. Additionally, describe clinical cases and compare the histologic changes in NB with and without detection of B burgdorferi.

METHODS

This was a retrospective multicenter cohort study (2013 to 2022). Medical records from horses with a diagnosis of NB and B burgdorferi PCR testing on NB tissue or synovial fluid were reviewed. The study population included 11 horses with a postmortem diagnosis of NB, 19 horses from the northeastern US with an antemortem diagnosis of B burgdorferi PCR-positive NB, and 15 healthy controls without evidence of NB and unvaccinated for B burgdorferi. Where serum was available, Lyme multiplex assay results were compared with controls and ELISAs targeting individual B burgdorferi antigens were performed. Histologic findings in nuchal bursa tissue were compared between NB cases with and without B burgdorferi PCR detection.

RESULTS

Serum OspA antibody values in B burgdorferi-positive NB cases (n = 13) were significantly elevated (P < .001) compared to controls (15), and OspA was the predominant antigen detected by ELISA (8). Histopathology did not vary between NB cases with (n = 9) and without (6) B burgdorferi PCR detection.

CONCLUSIONS

The presence of B burgdorferi in the nuchal bursa of horses is associated with increased serum OspA antibodies.

CLINICAL RELEVANCE: The role of B burgdorferi in equine NB may be underestimated, and targeted therapy requires investigation.