JPC SYSTEMIC PATHOLOGY

URINARY SYSTEM

November 2023

U-B02

 

SIGNALMENT (JPC #2132377): A Thoroughbred foal.

 

HISTORY: This foal died acutely.

 

HISTOPATHOLOGIC DESCRIPTION: Kidney: Multifocally affecting 40% of the renal cortex and less often the medulla are numerous 250-500µm diameter microabscesses that efface renal tubules, glomeruli, and interstitium. Microabscesses are composed of abundant eosinophilic cellular and karyorrhectic debris (lytic necrosis) admixed with numerous viable and necrotic neutrophils, fewer macrophages, lymphocytes, plasma cells, fibrin, hemorrhage, edema, and large colonies of basophilic, 1x2µm coccobacilli. Renal tubules are multifocally mildly ectatic and renal tubular epithelium is often degenerate with swollen and vacuolated cytoplasm or necrotic with hypereosinophilic cytoplasm and shrunken pyknotic nuclei. Tubular lumina contain variable amounts of debris and proteinaceous fluid and there is occasional mineralization within medullary tubules. Multifocally, blood vessels are lined by hypertrophied (reactive) endothelial cells and the interstitial capillaries are often congested with multifocal areas of interstitial hemorrhage. 

 

MORPHOLOGIC DIAGNOSIS: Kidney: Nephritis, embolic, suppurative, subacute, multifocal, moderate, with large colonies of coccobacilli and tubular degeneration and necrosis, Thoroughbred, equine.

 

ETIOLOGIC DIAGNOSIS: Renal Actinobacillosis

 

CAUSE: Actinobacillus equuli       

 

CONDITION: Sleepy foal disease; septicemia of foals; navel-ill; joint-ill, foal shigellosis

 

GENERAL DISCUSSION:  

·    Gram-negative, non-sporulating coccobacilli of the family Pasteurellaceae

• Causes highly fatal septicemia of newborn foals with failure of passive transfer
• Most common cause of embolic nephritis in horses

 

PATHOGENESIS:  

• Actinobacillus equuli subsp. equuli and Actinobacillus equuli subsp. haemolyticum are both normal inhabitants of the alimentary and reproductive tracts
• Transmission can occur in utero, during parturition, or via post-natal umbillical infection 
• Bacteremia results in showers of septic emboli that frequently lodge in small capillaries, particularly in the glomerular tufts, causing microabscesses throughout the renal cortex; necrosis often obliterates the glomeruli; microabscesses in other organs such as liver, adrenal glands, and joints
• Can cause septicemic diseases in adult horses with concurrent infection or immunosuppression

 

TYPICAL CLINICAL FINDINGS:  

• Fever, prostration, and diarrhea/hemorrhagic enteritis
• Inability to stand and/or nurse
• Swollen, hot, and painful joints
• Most infected foals die within the first three days after birth

 

TYPICAL GROSS FINDINGS:  

• Kidney: Multiple cortical green-yellow purulent foci up to 3 mm diameter, uniformly distributed throughout cortex
• Joints: Fibrinopurulent polyarthritis and polysynovitis
• Liver, adrenal glands, viscera: Multiple small (up to 3 mm) abscesses
• Hemorrhagic pneumonia 

       

TYPICAL LIGHT MICROSCOPIC FINDINGS:  

• Kidney: Multiple microabscesses within the cortex originating from glomerular and intertubular capillaries; contain bacterial colonies and variable numbers of neutrophils; hemorrhage within the medulla

• Joints: Fibrinopurulent polyarthritis and polysynovitis

• Lungs: Multifocal microabscesses in the interstitium in association with small vessels
• In a recent study of non-racehorses, A.equuli subsp. haemolyticus was the third most common bacteria isolated from cases of bronchopneumonia (Rahman 2022)

 

ADDITIONAL DIAGNOSTIC TESTS: 

 

DIFFERENTIAL DIAGNOSIS:

Acute septicemia/synovitis/arthritis (due to failure of passive transfer):  

• Escherichia coli  
• Klebsiella sp.
• Streptococcus sp.
• Rhodococcus equi (P-B06)
• Salmonella sp.

 

COMPARATIVE PATHOLOGY: 

Embolic suppurative nephritis in other species:

• Pig: Erysipelothrix rhusiopathiae (U-B09), Streptococcus sp., Corynebacterium sp.

• Cattle: Truperella pyogenes from valvular endocarditis
• Sheep and goats: Corynebacterium pseudotuberculosis (H-B06)
• Dogs: Prototheca zopfii (D-F03)

 

Disease-causing Actinobacillus sp.:

• Actinobacillus equuli: Septicemia in foals (occasionally in pigs and calves; rarely adult horses)

• Actinobacillus suis: Septicemia in piglets and fibrinous pericarditis in horses
• Actinobacillus lignieresii: Wooden tongue in cattle
• Actinobacillus seminis: Epididymitis and polyarthritis in lambs
• Actinobacillus capsulatus: Arthritis in laboratory rabbits
• Actinobacillus pleuropneumoniae: Porcine contagious pleuropneumonia
• Actinobacillus salpingitis: Salpingitis and peritonitis in chickens

 

REFERENCES:  

1. Cianciolo RE, Mohr FC. Urinary system. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier Saunders; 2016:432-433,452.
2. Rahman A, Uzal FA, Hassebroek AM, Carvallo FR. Retrospective study of pneumonia in non-racing horses in California. J Vet Diagn Invest. 2022;34(4):587-593.
3. Schlafer DH, Foster RA. Female genital system. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. 6th ed. Vol. 3. Philadelphia, PA: Elsevier Saunders; 2016:417-418. 
4. Stanton JB, Zachary JF. Mechanisms of Microbial Infections. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7^th ed. St. Louis, MO: Elsevier. 2022; 219.
5. Sula MM, Lane LV. The urinary system. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7^th ed. St. Louis, MO: Elsevier. 2022; 733, 746.
6. Uzal FA, Plattner BL, Hostetter JM. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier Saunders. 2016: 114.
7. Van Wettere AJ, Bown DL. Hepatobiliary System and Exocrine Pancreas. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7^th ed. St. Louis, MO: Elsevier. 2022; 515-516.

 

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