Detection of pathogenic Leptospira bacteria in pinniped populations via PCR and identification of a source of transmission for zoonotic leptospirosis in the marine environment

Abstract

Leptospirosis, caused by the spirochete Leptospira, is a geographically widespread disease that affects a broad range of mammals, including marine mammals. Among pinniped populations, periodic epizootics of leptospirosis are responsible for significant die-offs. Along the west coast of North America, the most recent leptospirosis epizootic occurred in 2004, during which samples were collected from cases ranging from California to British Columbia. The primary objective of this study was to use this well-defined sample set to determine the feasibility of using PCR techniques to diagnose Leptospira infection among pinniped populations in comparison with diagnostic methodologies commonly used for marine mammals. Successful amplification was achieved from a variety of samples, including freshly collected urine, urine stored at -80 degrees C for less than 6 months, and kidney (freshly collected, frozen, and decomposed), as well as feces- and urine-contaminated sand collected in the vicinity of a live-stranded animal. Pathological examination of tissue collected from Leptospira-infected animals revealed the presence of leptospiral antigen in the kidneys. The use of species-specific primer pairs revealed a pattern of host specificity for Leptospira interrogans in sea lions and Leptospira kirschneri in elephant seals. These studies indicate PCR is a sensitive and specific diagnostic tool for the detection of Leptospira infection in pinnipeds and reveal a potential source for epizootic, enzootic, and zoonotic spread of leptospirosis in a marine environment.

FIG. 1.

Images taken from a California sea lion with leptospirosis. (A) Photomicrograph of a hematoxylin and eosin-stained section of kidney illustrating numerous lymphocytes and plasma cells infiltrating the renal cortical interstitium. Tubules are occasionally ecstatic, lined by flattened epithelial cells and contain eosinophilic fluid, necrotic epithelial cells, and neutrophils (arrows). (B) Photomicrograph of immunohistochemistry for Leptospira sp. demonstrating positive staining in renal interstitial inflammatory cells and of spirochetes within renal tubules (arrows). Images A and B were taken from case 16 (CSL6176).