JPC SYSTEMIC PATHOLOGY

URINARY SYSTEM

November 2023

U-B04

 

SIGNALMENT (JPC # 1549986): German shepherd dog

 

HISTORY: Tissue from a German shepherd military working dog which had several episodes of epistaxis and seemed lethargic.

 

HISTOPATHOLOGIC DESCRIPTION: Kidney: Multifocally expanding the renal interstitium predominantly at the corticomedullary junction and radiating into the medulla and cortex, surrounding small vessels and widely separating tubules, are abundant plasma cells, fewer lymphocytes, and macrophages. Multifocally within affected areas, tubules are lost, shrunken (atrophy), or ectatic and lined by attenuated epithelium. Remaining tubular epithelium in affected areas often display one of the following changes: swollen with loss of cellular detail and intracytoplasmic vacuoles (degeneration); shrunken with hypereosinophilic cytoplasm and condensed, pyknotic nuclei (necrotic); or are occasionally sloughed into tubular lumina. Occasionally tubule lumina contain pale homogenous eosinophilic fluid (tubular proteinosis). Few glomeruli have mild periglomerular fibrosis. Multifocally within the medulla, away from the corticomedullary junction, similar plasma cell rich infiltrates surround vessels, tubules, and glomeruli. In less affected areas, tubular epithelium often contains a golden-brown intracytoplasmic pigment (hemosiderin and/or lipofuscin).

 

MORPHOLOGIC DIAGNOSIS: Kidney: Nephritis, interstitial and perivascular, plasmacytic, chronic, multifocal, moderate, with mild tubular necrosis, atrophy, and degeneration, German shepherd dog, canine.

 

ETIOLOGIC DIAGNOSIS: Renal ehrlichiosis

 

CAUSE: Ehrlichia canis

 

CONDITION: Tropical canine pancytopenia, canine hemorrhagic fever, monocytic ehrlichiosis

 

GENERAL DISCUSSION:

• E. canis is a tick-transmitted, gram negative, obligate intracellular, rickettsial bacterium that replicates and spreads within mononuclear cells
• The vector and reservoir is the brown dog tick, Rhipicephalus sanguineous
• Canids (domestic dogs, coyotes, foxes, and jackals) are the reservoir hosts, rarely cats are infected
• German shepherd dogs are more susceptible to severe infection 
• E. canis is the primary agent of canine ehrlichiosis but other agents and co-infections with other rickettsioses play a significant role 

 

PATHOGENESIS:

• Endothelial cell, platelet, and leukocyte dysfunction
• Infected tick feeds on host; salivary secretions contaminate the feeding site and organisms multiply in macrophages of the mononuclear-phagocyte system during the incubation period (8 to 20 days) and then spread throughout the body
• Organism survives and multiplies intracellularly by inhibiting phagosome-lysosome fusion
• The subsequent course of the disease is divided into three phases: acute (can clear via CMI), subclinical (persists in mononuclear cells), and chronic (see below)

 

TYPICAL CLINICAL FINDINGS:

• Non-specific clinical signs; diagnosis often made during the chronic phase
• Three phases of disease: Acute, subclinical, and chronic
  1. Acute phase (2 - 4 weeks): Fever, oculonasal discharge, anorexia, depression, petechiae, ecchymoses, lymphadenomegaly and splenomegaly 
  2. Subclinical phase (40-120 days): Dog may appear clinically normal; if immunocompetent the animal may eliminate the organism 
  3. Chronic phase: Impaired bone marrow production resulting in pancytopenia; can be asymptomatic, mild or severe; mild – weight loss, mild hematologic changes; severe – epistaxis, generalized hemorrhage, pallor, severe weight loss, anterior uveitis, retinal hemorrhage, neurologic signs, protein-losing nephropathy

 

TYPICAL CLINICAL PATHOLOGY FINDINGS:

• Thrombocytopenia; exhibit a reduction in both platelet adhesiveness and aggression; suspect antiplatelet antibodies 
• Non-regenerative anemia (may be regenerative in acute phase)
• Hyperproteinemia: Polyclonal or monoclonal hypergammaglobulinemia 
• Advanced disease: Marked lymphocytosis composed of large granular lymphocytes; this is an immune response 
• Lymphocytosis
  1. Clonal rearrangements of the TCR gene have been detected in dogs with E. canis infections; one of the few non-neoplastic causes of a monoclonal gammopathy; E. canis almost exclusively causes expansion of CD8 T-cells that have granules in their cytoplasm; CD8 T-cells do not exhibit aberrant antigen expression (neoplastic cells are more likely to exhibit aberrant antigen expression); not known to cause clonal expansion of B-lymphocytes 
• Chronic E. canis may cause aplastic anemia with pancytopenia by an unknown mechanism
• Intracellular inclusions (morulae), usually in monocytes; inclusions may also be seen in lymphocytes and even more rarely in neutrophils (morulae in neutrophils more consistent with Anaplasma phagocytophilum or E.ewingii)
• Increased buccal mucosal bleeding time secondary to thrombocytopenia and hypofunctional platelets (reduced adhesiveness and aggregation)
• Proteinuria secondary to glomerulonephritis

 

TYPICAL GROSS FINDINGS:

• Hemorrhages, petechial to ecchymoses, in subcutis and major organs: Lungs, heart, gastrointestinal and urinary tracts, and eye; also in meninges, kidney, testes
• Bone marrow is hyperplastic and red in acute disease, but becomes hypoplastic and pale in dogs with chronic infection

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Generalized perivascular lymphoplasmacytic infiltrate mostly within kidneys, meninges, and hematopoietic tissue
• Hemorrhage in multiple organs
• Minimal change disease: Glomerular changes are slight, but clinical disease is marked; reversible global fusion of podocyte foot processes and significant proteinuria; produced experimentally with E. canis infection
• Kidneys: Canine glomerular amyloidosis has been associated with chronic E. canis
• Eye: Characteristic retinal changes including anterior uveitis, chorioretinitis, papilledema, and retinal hemorrhage 

 

ULTRASTRUCTURAL FINDINGS:

• Ehrlichia morulae are characteristically intracytoplasmic within a membrane bound vacuole; the vacuole contains many individual double-membrane organisms in various stages of development
• Minimal change glomerulonephropathy: Reversible global fusion of podocyte foot processes with significant proteinuria 

 

ADDITIONAL DIAGNOSTICS:

• Direct examination of E. canis morulae in peripheral blood buffy coat smears, tissue aspirates, and CSF fluid; often unreliable because only a few cells are infected; examination of buffy coat smears and lymph node aspirates have the highest sensitivity
• Morulae found in monocytes and lymphocytes are rounded, one-third to one-half the diameter of an erythrocyte with a granular internal structure consisting of basophilic elementary bodies each 0.5-1.0 micron in diameter

 

DIFFERENTIAL DIAGNOSIS:

Other canine rickettsial organisms:

• Ehrlichia ewingii: Canine granulocytic ehrlichiosis (CGE); found in neutrophils and eosinophils; milder disease; associated with polyarthritis and lameness; serologically cross reactive to a limited degree with E. canis
• Anaplasma phagocytophilum (Ehrlichia equi, Ehrlichia phagocytophila): Canine granulocytotropic anaplasmosis (CGA); found in neutrophils and rarely in eosinophils; can infect dogs, horses, and cats; milder disease than E. canis and ocular lesions more often seen with E. canis ; P-selectin ligand-1 is the neutrophil surface receptor the bacteria binds to (facilitates endocytosis)
• Anaplasma platys (Ehrlichia platys): Thrombocytotropic anaplasmosis; canine infectious cyclic thrombocytopenia; infects and replicates within platelets; causes recurrent marked thrombocytopenia; few clinical signs; infection often concurrent with E. canis infection
• Ehrlichia chaffeensis: The agent of human monocytic ehrlichiosis; infection has been reported in dogs
• Neorickettsia risticii (subsp. atypicalis): Causes little if any disease in experimentally infected dogs and cats; dynamics in natural infection are unknown
• Rickettsia rickettsii (N-B09): Rocky Mountain spotted fever; necrotizing vasculitis of small veins, capillaries, and arterioles; invades small vessels and replicates in endothelial cells; similar microscopically and clinically to acute phase of E. canis; more severe as the disease progresses; differentiate by direct FA and histopathology
• Neorickettsia helminthoeca (salmon poisoning, H-B10): Lesions resemble those of E. canis, but infection is usually fatal in 15 days; eggs of Nanophyetus salmincola may be found in the intestine
• Wolbachia sp: A closely related bacteria to Ehrlichia and Anaplasma; when this bacterium is present in Dirofilaria immitis infections, clinical signs are typically more severe; this genus has previously only been considered a pathogen of arthropods and helminths

 

Other causes of thrombocytopenia, anemia, or prolonged bleeding time:

• Estrogen toxicity, factor VIII related antigen deficiency, and disseminated intravascular coagulation (DIC): Can usually be differentiated clinicopathologically and histopathologically
• Borrelia burgdorferi (Lyme disease)(U-B01): Lymphoplasmacytic interstitial nephritis with glomerulonephritis
• Leishmania (U-P03): Circulating immune complexes deposit in walls of blood vessels causing glomerulonephritis and renal failure

 

Other causes of monoclonal gammopathy

• Neoplastic (most common): lymphoid neoplasia including plasma cell myeloma, lymphoma, chronic lymphocytic leukemia
• Non-neoplastic (uncommon): canine amyloidosis, canine visceral leishmaniasis, feline infectious peritonitis, plasmacytic gastroenterocolitis

 

Miscellaneous: Acute canine polyradiculoneuritis (model for the acute axonal form of Guillain-Barre syndrome): Serologic evidence rules out E. canis as the cause and serologically is linked to Toxoplasma gondii as the cause

 

COMPARATIVE PATHOLOGY:

• Lemur colony (south-central U.S.): anorexia, lethargy, fever, and enlarged lymph nodes; thrombocytopenia and leukopenia were common; hyperbilirubinemia, azotemia, and proteinuria were occasionally detected 
• Implicated as a positive agent causing infectious joint disease 

Selected rickettsial diseases in other animals:

• Ruminants
  • Ehrlichia ruminantium causes pericardial effusion (heartwater; cowdriosis) in ruminants; endemic in sub-Saharan Africa; pericardial effusion in small ruminants (may be absent in cattle); brain lesions common, especially in cattle, and include cerebellar petechial hemorrhages and a thickened choroid plexus
  • Cattle: Bovine ehrlichiosis caused by Anaplasma marginale or A. centrale (A. centrale limited to South America, Africa, and the Middle East)
  • Sheep and goats: Ovine and caprine ehrlichiosis caused by A. ovis
  • Cattle, sheep and goats: “Pasture fever” in cattle and “tick-borne fever” in sheep and goats; mild, nonfatal febrile disease in Europe caused by A. phagocytophilum
• Horses: Potomac horse fever (equine monocytic ehrlichiosis; equine ehrlichial colitis) caused by Neorickettsia risticii; transmitted by ingestion of trematodes within freshwater snails; biphasic fever, depression, severe diarrhea, dehydration, and laminitis; +/- colic and subcutaneous edema of the thorax, abdomen, and hind legs; predilection for monocytes and enterocytes 
• Cats: Feline ehrilichiosis caused by E. canis or A. phagocytophilum

 

REFERENCES:

1. Barger AM. Musculoskeletal System. In: Raskin RE, Meyer DJ, eds. Canine and Feline Cytology: A Color Atlas and Interpretation Guide. 4th ed. St. Louis, MO: Elsevier; 2023:490.
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