Evaluation of Two Serologic Tests for Rapid Detection of Anti-Leptospira Antibodies in California Sea Lions (Zalophus californianus)

Leptospirosis is a bacterial zoonosis impacting wild and domestic animals globally. Leptospira interrogans serovar Pomona is endemic in free-ranging California sea lions (CSLs; Zalophus californianus), and leptospirosis is frequently diagnosed in stranded CSLs. Serum microscopic agglutination test (MAT) is a commonly performed diagnostic assay, and CSLs with clinical disease have reliably elevated MAT titers. However, MAT results may not be available for several days after sampling. Given the zoonotic and high transmission potential of Leptospira spp., a point-of-care diagnostic test would be valuable in rehabilitation and managed care settings and during outbreak response efforts. The IDEXX SNAP and Zoetis WITNESS anti-Leptospira antibody tests are rapid diagnostic tools that have been validated in dogs and give a qualitative (positive or negative), not quantitative (exact titer), result. The SNAP test uses ELISA to detect both immunoglobulin (Ig)M and IgG antibodies, whereas the WITNESS test is a lateral flow assay that only detects IgM. We compared SNAP and WITNESS results with MAT results by using serum collected from stranded and free-ranging CSL with negative, low, medium, and high anti-Leptospira antibody titers as previously determined by MAT. Percent agreement between SNAP and MAT results was high, with a Cohen's kappa statistic of 0.957. No WITNESS tests were positive. These findings suggest that the SNAP test may be useful for detecting anti-Leptospira antibodies and ruling out leptospirosis in CSL.