COMPANION ANIMALS

Leptospiral nephritis in a Shih Tzu dog

Margaret Stalker, Jessika Bronsoiler

A 4-year-old spayed female Shih Tzu living in Brantford, Ontario, was presented with a history of partial anorexia of one-month duration. Clinical workup had been previously refused, and the dog had been treated symptomatically with famotidine. On presentation, the dog was dehydrated and severely azotemic. The dog was hospitalized, treated with intravenous fluids, antibiotics, and antiemetics without significant improvement and the owner elected euthanasia. Sections of kidney collected at postmortem were submitted for histologic examination at the AHL.

Histology revealed extensive renal interstitial inflammatory infiltrates (Fig. 1), with accompanying mild interstitial fibrosis and tubular atrophy. The inflammatory infiltrate was of mixed cell types, with nodular aggregates as well as more diffuse infiltrates of lymphocytes and plasma cells, scattered macrophages, and infiltrates of neutrophils within the cortical interstitium. There was edema and patchy irregular foci of fibrin exudation and neutrophilic infiltrates within the medullary interstitium. The unusually severe and active inflammation of this lymphoplasmacytic and suppurative tubulointerstitial nephritis prompted us to perform immunohistochemistry, looking for Leptospira interrogans. Widespread positive staining was present (Fig. 2), including extensive intense linear and granular staining (the latter representing degraded bacteria) within tubular lumens, tubular epithelial cells, and also within macrophages in the interstitium. Staining with Warthin-Starry silver stains also highlighted intact organisms morphologically compatible with leptospires in renal tubular lumens (Fig. 3).

Naturally occurring infection with Leptospira spp. is relatively common in various wildlife populations in southern Ontario, principally raccoons and striped skunks. Infection in these species is apparently self-limiting and asymptomatic, with the host recovering from the initial stages of the disease while potentially remaining as a reservoir capable of continued urinary shedding of infectious bacteria. Epidemiologic studies of canine leptospirosis demonstrate increased risk of infection in middle-aged, intact male hounds, herding, working or mixed-breed dogs, presumably associated with increased outdoor activity of these breeds. However, the presence of large urban populations of reservoir wildlife species such as raccoons increases the chance of exposure of urban dogs with access to the outdoors as well.

The severe lymphoplasmacytic and neutrophilic tubulointerstitial nephritis seen in this case is a compatible lesion of subacute infection in dogs, although acute infections may cause significant hepatorenal dysfunction (with depression, anorexia, vomiting, diarrhea, icterus, dehydration, severe azotemia) with only minimal, subtle histologic lesions in the kidney and liver. Antemortem diagnosis has relied on detection of high serum antibody titers using the microscopic agglutination test (MAT), although peracute/acute infections may have low titers. PCR testing of blood or urine, and immunohistochemistry on renal biopsies may be useful for detection of early infections and confirmation of infection in some instances.