Diagnostic testing for Leptospirosis in California sea lions (Zalophus californianus)

Authors: DUNCAN, COLLEEN - Colorado State University; WHEELER, LIZ - Colorado State University; Zuerner, Richard; GULLAND, FRANCES - Marine Mammal Center

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2011
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Leptospirosis is a relatively common bacterial disease in California sea lions (Zalophus californianus); however, there remain gaps in our understanding of maintenance hosts relative to animals demonstrating clinical disease. To effectively study the epidemiology of leptospirosis in any species, a solid understanding of the performance of diagnostic assays at different stages of infection is required. This study compares renal histopathology to immunohistochemistry (IHC) and polymerase chain reaction (PCR) for detection of Leptospira interrogans in California sea lions with and without evidence of clinical renal disease. Animals included in this study were stranded California sea lions presenting to The Marine Mammal Center in Sausalito, CA, between July 1, 2008, and March 30, 2009, that either died or were euthanized due to the presence of acute disease. Animals were examined post mortem and both fresh (for PCR) and fixed kidney (for histopathology and IHC) tissue was available for diagnostic testing. One hundred and thirty-four animals met the criteria for inclusion during the study period; 42 with clinical renal disease, 25 with no ante-mortem changes consistent with renal disease, and 67 with no ante-mortem blood work. Of 134 kidneys, 35 were positive for Leptospira interrogans on PCR; all of those kidneys were also positive on IHC as were an additional 17 kidneys that were PCR negative. The kappa value (agreement) between the two tests was 0.71 (95% CI 0.55-0.88). Discordant results between the two tests had no unique histologic or host characteristics and both the histologic lesions and IHC staining pattern was morphologically consistent with leptospirosis. Histologic lesions were present in the kidneys of 109 (81%) animals. The most common histologic change was interstitial lymphoplasmacytic inflammation that was either patchy or more regionally extensive and associated with tubular changes. This latter pattern along with severity of inflammation of was statistically associated with Leptospira infection. Tubular lesions (most commonly suppurative tubulitis with tubular degeneration) and glomerular lesions (glomerulonephritis) were observed in 57 (43%) animals and animals with these changes were also more likely to be infected. Not surprisingly, animals with clinical renal disease were more likely to be positive than those with no ante-mortem chemistry changes; however, two animals were positive on IHC in the absence of serum chemistry changes. Males were significantly more likely to be IHC positive than females and were also more likely to be positive on IHC in the absence of ante-mortem clinical disease, which may be consistent with characteristics of an asymptomatic or carrier animal. Results of this study suggest that IHC may be a more sensitive tool relative to PCR for diagnosis of Leptospira infection in California sea lions when using kidney tissue. Severity and pattern of histologic changes in the kidney are associated with leptospirosis but non-clinical animals can also be positive suggesting that elucidation of recovered or asymptomatic infection may play a role in maintenance of infection within populations.