A study was conducted to identify a population of dogs with renal pathologic lesions consistent with Lyme nephritis to determine the Lyme status of these dogs and if intact B burgdorferi organisms or other bacteria were present. Case inclusion criteria: diagnostic renal sample(s) in paraffin blocks or frozen with histopathology consistent with Lyme nephritis and serologic evidence of natural exposure to B burgdorferi (Western blot or C6 antibody test). Inclusion criteria for the control dogs: diagnostic renal sample(s) in paraffin blocks with glomerular lesions and serologic documentation of lack of natural exposure to B burgdorferi (enzyme-linked immunosorbent assay, Western blot, or C6 antibody test). Twenty-six affected and 10 control dogs met these criteria. Minimal to no evidence of intact B burgdorferi organisms in the kidneys of dogs with serology and histopathology consistent with Lyme nephritis was found.
Immunohistochemistry (IHC) and polymerase chain reaction (PCR) were negative in all cases assessed, and fluorescence in situ hybridization (FISH) was positive for the presence of a single B burgdorferi organism in 2 cases. The significance of finding a single organism in these 2 cases is unclear, as visualization of multiple organisms in a single tissue sample is usually required to make a definitive diagnosis of an infectious disease. Several cases were strongly positive for the presence of eubacteria, suggesting that a secondary eubacterial infection could have been present. The authors concluded that direct renal invasion by B burgdorferi organisms does not appear to be responsible for the Lyme nephritis syndrome, and proposed that this syndrome may occur secondary to Lyme antigen-associated immune complex deposition in the glomeruli, leading to a postinfectious glomerulonephritis.
COMMENTARY: The syndrome of nephritis seen in some dogs with Lyme disease is still a puzzle: this study determined that there were no intact Borrelia burgdorferi organisms in the kidney causing the damage. Other speculated causes that need to be studied include an immune complex disease or an additional coinfecting organism as yet to be identified. Since recent studies have identified B burgdorferi-specific circulating immune complexes in the serum of Lyme infected dogs, the next logical step is to see if these immune complexes could be the cause of this syndrome.
