We hypothesized that renal glomerulopathy is a common finding in dogs with subclinical ehrlichiosis. The aim of this study was to evaluate renal cortex biopsies in four dogs with subclinical ehrlichiosis diagnosed by PCR and enzyme-linked immunosorbent assay (ELISA). Dogs with clinical signs, comorbidities or azotemia were excluded. Biopsy material was examined with light microscopy and immunofluorescence (IF). Sections were stained with hematoxylin and eosin, periodic acid-Schiff, Jones methenamine silver, Masson´s trichrome, and Congo Red. For direct IF, fresh renal specimens were embedded in optimal cutting temperature compound and snap-frozen in liquid nitrogen. Sections were incubated with FITC-labeled goat anti-dog IgA, IgG, IgM, or complement C3 antibodies.
Urine protein-to-creatinine ratio (UPC) was elevated (> 0.5) in two dogs and normal (< 0.5) in two dogs. Renal lesions were observed in all dogs with ehrlichiosis, including: thickened glomerular basement membranes (n = 2), mesangial cell proliferation (n = 3), focal segmental glomerulosclerosis (FSGS) (n = 1), synechiae (n = 2), and interstitial fibrosis and tubular atrophy (IFTA) (n = 1). On IF, all dogs demonstrated granular moderate to strong glomerular mesangial and capillary wall staining with antibodies against IgM. One dog also had weak positivity for C3 and another dog had moderate positivity for all immunoreactants.
It is well-recognized that glomerular immune complex deposition can cause renal injury. In view of the histologic evidence of renal lesions and frequent immunoglobulin staining in this preliminary study, we suggest that ehrlichiosis without clinical signs is a potential cause of renal disease in dogs and should be investigated even in animals with lower UPC.