History

A 3-year-old spayed female pit bull–type dog was evaluated on an emergency basis because of anorexia and vomiting of 3 to 4 days' duration. The illness started after the introduction of a puppy obtained at a hog festival into the household; that puppy was evaluated by another veterinarian who made a presumptive diagnosis of parvovirus infection. The puppy was treated supportively but died during treatment. In addition, 2 other dogs owned by the family had died after a brief illness following the introduction of the puppy.

Clinical and Gross Findings

At the emergency evaluation, the dog's rectal temperature was 39.67°C (103.4°F), and its mucous membranes were hyperemic and dry. A blood sample was collected and tested^a for Dirofilaria immitis antigen and antibodies against Borrelia burgdorferi and Ehrlichia canis; results were negative. Results of fecal floatation were also negative. Serum biochemical analysis and a CBC were performed. The dog had high BUN (72 mg/dL; reference range, 7 to 27 mg/dL), creatinine (12.3 mg/dL; reference range, 0.5 to 1.8 mg/dL), phosphate (10.6 mg/dL; reference range, 2.5 to 6.8 mg/dL), total protein (8.9 g/dL; reference range, 5.2 to 8.2 g/dL), globulin (5.3 g/dL; reference range, 2.5 to 4.5 g/dL), chloride (375 mg/dL; reference range, 110 to 320 mg/dL), and potassium (6.3 mmol/L; reference range, 3.5 to 5.8 mmol/L) concentrations; high alkaline phosphatase activity (219 U/L; reference range, 23 to 212 U/L); high WBC (20.46 × 10³ WBCs/μL; reference range, 5.5 × 10³ WBCs/μL to 16.9 × 10³ WBCs/μL) and neutrophil (15.03 × 10³ neutrophils/μL; reference range, 2.0 × 10³ neutrophils/μL to 12.0 × 10³ neutrophils/μL) counts; and a low RBC count (5.13 × 10⁶ RBCs/μL; reference range, 5.5 × 10⁶ RBCs/μL to 8.5 × 10⁶ RBCs/μL). Based on the clinical signs, the dog was treated with antimicrobials and fluid therapy. The values of renal function variables progressively increased, and at the time of euthanasia, BUN concentration was > 130 mg/dL, creatinine concentration was > 13.6 mg/dL, and potassium concentration was 7.6 mmol/L. The dog was euthanized because of the poor prognosis and submitted for necropsy. The duration of illness from the emergency evaluation to euthanasia was 10 days.

At necropsy, the dog's mucous membranes were pale. The abdominal cavity contained approximately 6 L of serosanguineous fluid (ascites). Both kidneys were enlarged (weight of left kidney, 199 g; weight of right kidney, 225 g) and congested (Figure 1). On cross section of both kidneys, pale white streaks extended from the cortex to the medulla. The liver was slightly enlarged, and the spleen was dark and appeared spongy. The lungs were congested and had a focal area of atelectasis. No other major gross lesions were observed.

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Photographs of the kidneys of a 3-year-old female pit bull–type dog that was euthanized because of severe renal disease. A—Grossly, both kidneys are enlarged with congested blood vessels. B—Cut surface view of the right kidney. Notice the pale white streaks that extend from the cortex to the medulla. The left kidney also had similar changes.

Citation: Journal of the American Veterinary Medical Association 240, 8; 10.2460/javma.240.8.957

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Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn page →

Histopathologic Findings

Sections of the lungs, kidneys, spleen, liver, small and large intestines, salivary glands, brain, and eyes were examined histologically. The lungs, kidneys, spleen, and liver tissues were diffusely and moderately congested. In the kidney tissue sections, large numbers of plasma cells and neutrophils and a lesser number of lymphocytes and few macrophages admixed with collagen fibers and fibroblasts diffusely and markedly expanded the renal cortical and medullary interstitium. The inflammatory cells surrounded the degenerate, necrotic, atrophic, and occasionally regenerating renal tubules (Figure 2). The renal tubular lumens were filled with proteinaceous casts, aggregates of inflammatory cells, and cellular debris. Scattered tubules contained oxalate crystals. There were multifocal areas of interstitial hemorrhage. The glomeruli were moderately hypercellular and had mildly thickened mesangium and variably thick capillary basement membranes.

In the sections of the liver, aggregates of several lymphocytes and scant collagen fibers multifocally disrupted the parenchyma. There were a few lymphocytes and plasma cells in the periportal spaces. In 1 section of liver tissue, multifocal periportal areas contained large numbers of eosinophils admixed with several epithelioid macrophages and few lymphocytes and plasma cells. In the sections of the small intestine, the lamina propria was expanded by few to several plasma cells, lymphocytes, and eosinophils, and the capillaries were congested. The submucosal blood vessel in a section of colon had fibrinoid necrosis of the vessel wall and was surrounded by several lymphocytes, plasma cells, eosinophils, macrophages, and reactive fibroblasts. Multifocally, aggregates of lymphocytes and plasma cells and rare eosinophils infiltrated the interstitium of the salivary glands. Unilaterally expanding the submucosal stroma of the third eyelid and surrounding the glands were several lymphocytes and plasma cells. Moderate numbers of plasma cells and few neutrophils diffusely infiltrated the splenic red pulp; the splenic periarteriolar lymphoid sheaths were hyperplastic.

Additional Laboratory Findings

On the basis of the clinical and clinicopathologic findings, renal failure due to an infectious disease was suspected. Results of antemortem testing of urine by use of fluorescent antibody test and PCR assay were positive for Leptospira sp. Microscopic agglutination testing against 7 serovars of Leptospira was performed on a serum sample obtained from the dog. The following titers were obtained for each serovar at the initial evaluation and at the time of euthanasia, respectively: Leptospira interrogans serovar Pomona, 400 and 800; Leptospira interrogans serovar Canicola, 200 and 200; Leptospira interrogans serovar Icterohemorrhagiae, not detected and 100; Leptospira interrogans serovar Bratislava, 200 and 800; Leptospira interrogans serovar Grippotyphosa, 3,200 and 6,400; Leptospira interrogans serovar Autumnalis, 1,600 and 6,400; and Leptospira interrogans serovar Hardjo, not detected and not detected. Although the highest titers were those against serovars Grippotyphosa and Autumnalis, a definitive identification of the infecting serovar could not be made. Immunohistochemical and PCR analyses and fluorescent antibody staining of kidney samples obtained after death also yielded positive results for Leptospira sp (Figure 2).

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Photomicrographs of sections (A–C) and an impression smear preparation (D) of the kidneys of the dog in Figure 1. A—Low-power photomicrograph of a section of a kidney. Notice the severe lymphoplasmacytic interstitial nephritis. H&E stain; bar = 100 μm. B—Photomicrograph of the same section of a kidney. Notice the lymphoplasmacytic interstitial nephritis and tubular necrosis. H&E stain; bar = 50 μm. C—Photomicrograph of a section of a kidney following immunohistochemical staining with polyclonal anti-Leptospira antibody. Notice the presence of Leptospira antigen staining inside the tubular epithelium and cells in the interstitium (arrows). Bar = 50 μm. D—Photomicrograph to illustrate the results of fluorescent antibody testing involving fluorescein isothiocyanate conjugate polyclonal anti-Leptospira antibodies in a kidney impression preparation. Notice the presence of an intact Leptospira organism (arrow).

Citation: Journal of the American Veterinary Medical Association 240, 8; 10.2460/javma.240.8.957

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Morphologic Diagnosis

Moderate to marked bilateral, diffuse lymphoplasmacytic nephritis with multifocal tubular proteinosis, degeneration, necrosis, and regeneration and mild multifocal, lymphoplasmacytic portal hepatitis.

Comments

For the dog of this report, the history did not suggest environmental exposure to a toxic compound, so the diagnostic investigation focused primarily on ruling out potential infectious causes. Diagnostic testing of antemortem clinical samples followed by postmortem histologic evaluation of tissue samples confirmed the diagnosis of leptospirosis.

Leptospirosis is caused by a spirochete belonging to the genus Leptospira. The disease is one of the most widespread, underdiagnosed, and fatal diseases in humans and other animals.¹ Although veterinarians are aware of the clinicopathologic features of leptospirosis, the disease remains underdiagnosed because the early stages of the disease have protean manifestations and can resemble many other febrile illnesses. The several species of Leptospira contain > 250 serovars that are grouped into several serogroups. Molecular characterization has classified this genus into 17 species.¹ These organisms are maintained in the renal tubules of domestic and wild animals. The prevalence of a particular serovar differs with geographic region and animal hosts. Currently, Leptospira spp serovars that more commonly cause disease in dogs are Grippotyphosa, Autumnalis, Bratislava, and Pomona.^2,3

In dogs, common clinical signs associated with leptospirosis include weakness, signs of depression, anorexia, vomiting, polyuria, polydipsia, diarrhea, oculonasal discharge, signs of renal and muscle pain, and icterus.⁴ The renal lesions associated with subacute leptospirosis are mainly characterized by interstitial nephritis,¹ as in the case described in the present report. Chronic effects include interstitial fibrosis and moderate interstitial nephritis. The pathogenesis and lesions of leptospirosis depend on the infecting serovar, species affected, and severity of infection.¹ In acute cases, pulmonary hemorrhage, tubulointerstitial nephritis, and hepatitis develop.⁵ Mild hepatitis in the dog of the present report was attributed to Leptospira infection. Although generalized endothelial damage and vasculitis are induced in acute leptospirosis, the focal area of mild vasculitis observed in the colon of the dog could have been unrelated to leptospirosis and might have been a residual lesion attributable to parasitic migration. Leptospirosis mainly results in tubulointerstitial lesions. Tubulointerstitial lesions can be caused by infections or immunologic disorders and many agents, including toxins, chemicals, and drugs.⁵ Unlike renal lesions induced by leptospirosis, nephritis associated with naturally occurring Lyme disease is characterized by glomerulonephritis, in addition to tubular necrosis and interstitial nephritis.⁶ Glomerulonephritis and plasmacytic interstitial nephritis can also develop in dogs infected with Ehrlichia canis.⁶ Ethylene glycol, oxalate, Amaranthus spp, and drugs such as gentamicin, tetracycline, and sulfonamides generally induce tubular lesions, and exposure to such agents should also be considered in cases in which clinical pathological findings are compatible with renal failure.⁵

Accurate and early diagnosis of leptospirosis in dogs is important for successful treatment and to prevent transmission to humans in veterinary practices and households. Detection of Leptospira organisms in blood and urine samples is the best diagnostic method in the early stage of infection. In the later stages of infection, as the disease progresses and involves multiple body systems, serologic analysis combined with the detection of Leptospira organisms generally provides more accurate results. Bacteriologic culture, although useful for epidemiological studies, is not recommended for diagnosis because of the slow growth rate of Leptospira spp and contamination of the cultured samples, which may preclude further evaluation.

Treatment of leptospirosis via administration of antimicrobials is essential. Antimicrobial treatment is effective and decreases disease severity if started early in the disease process.⁷ Antimicrobials such as penicillin, ampicillin, amoxicillin, and doxycycline are most effective.⁸ Severe renal disease and azotemia can be managed by hemodialysis.⁸

Vaccination with products containing L interrogans serovars Canicola and Icterohemorrhagiae appears to have decreased the incidence of the disease caused by these serovars in dogs. Because Grippotyphosa, Pomona, and Autumnalis are the currently prevalent Leptospira spp serovars causing disease in dogs, products containing these serovars are recommended.

In the case described in this report, precautions were advised to protect the hospital staff and the dog's owners from infection. The presumption was that the deaths of 3 other dogs in the household were due to leptospirosis and that the newly arrived puppy obtained at the hog festival was the source of infection.