JPC SYSTEMIC PATHOLOGY

CARDIOVASCULAR SYSTEM

March 2025

M-B03 (NP)

 

SIGNALMENT (JPC #2133912):  40-day-old male Cobb broiler chicken

 

History: This bird was from a commercial farm where mass culling was occurring. Veterinarian noted the birds had normal mentation but exhibited paresis or paralysis and had a characteristic posture of hock-sitting with legs extended in front of them and wing walking. Post-mortem examination of one bird showed a small bursa and femoral head necrosis.

 

HISTOPATHOLOGIC description:  Vertebrae, T4-T5: Obliterating and replacing 70% of the vertebrae is a multinodular fibrocartilaginous callus with proliferative woven bone overlying a fractured vertebra, that is dorsally displacing and compressing the overlying spinal cord. Within the compressed spinal cord, there is mild to moderate Wallerian degeneration characterized by vacuolation of the white matter with spheroids, degenerate microglia, and axonal vacuolation. There is hemorrhage, fibrin and edema within the grey matter. Within the fractured vertebra there is multifocal lytic necrosis characterized by loss of architecture with replacement by eosinophilic cellular and karyorrhectic debris. There is a focal granuloma with central necrotic debris, surrounded by heterophils and macrophages. Multifocally within areas of necrosis  and within the granuloma, there are large numbers of bacterial cocci colonies. The remaining bony trabeculae are lined by increased numbers of osteoclasts in Howship's lacunae (osteolysis) and there is moderate replacement with reactive fibroblasts (fibrosis). There are fragments of necrotic bone with empty lacunae (sequestrum). Admixed within these areas are eosinophilic fluid and increased clear space (edema), eosinophilic fibrillar material (fibrin), moderate amounts of hemorrhage, and moderate infiltration by heterophils, macrophages, lymphocytes, and plasma cells. Within areas of hemorrhage, there is both free and intrahistiocytic hemosiderin. 

 

Morphologic diagnosis:  Vertebrae, T4-T5: Osteomyelitis, heterophilic and lymphohistiocytic, chronic, regionally extensive, severe, with necrosis, pathologic fracture, callus formation, and spinal cord degeneration, avian, Cobb broiler chicken.

 

cause:  Enterococcus cecorum

 

Etiologic diagnosis:  Enterococcal spondylitis 

 

CONDITION: “Kinky back”

 

General discussion:

• Enterococcus spp. are gram (+), facultatively anaerobic cocci that are normal flora of the GI tract of many species
• Enterococcus cecorum is a known GI commensal of adult poultry, but pathogenic strains are reported to have a predilection for cartilage and bone; are known to cause spondylitis, septicemia, femoral head necrosis, osteomyelitis, pericarditis, endocarditis, perihepatitis, and splenomegaly (Dunman et al, 2023)
• Spondylitis (inflammation of an intervertebral disk and the contiguous vertebrae) is most often bacterial in origin, via a primary bacteriemia; can also be secondary to chronic infection some other source in the body
• Enterococcal spondylitis is also known as vertebral osteoarthritis or “kinky back” and affects primarily the free thoracic vertebrae (cranial to the synsacrum and caudal to the notarium) in chickens which are the only vertebrae in the thoracolumbar spine of chickens that have weight-bearing articulations and functions to transfer body weight to the hips and hind limbs – may be a predisposing factor to infection
• Worldwide distribution, most common in broiler chickens; also known to cause septicemia in Pekin ducklings and racing pigeons. 
• NOTE: “kinky back” is also used to refer to a genetic spondylolisthesis in chickens that is unrelated to enterococcal spondylitis
• Reovirus coinfection (Dunnam et al, Avian diseases, 2023):
  1. A recent study isolated avian reovirus from tendons in 70% of cases of E. cecorum septicemia; represents significant coinfection
  2. Reovirus could possibly be exacerbating occurrence and severity of E. cecorum septicemia due to immunosuppressive actions of reovirus

 

Pathogenesis:

• Intestinal colonization of a pathogenic E. cecorum à bacteremia à hematogenous spread to free thoracic vertebrae (+/- OCD lesions) à colonization of free thoracic vertebrae and its articulations à spondylitis 
• Infection of free thoracic vertebrae has been linked to osteochondrosis dissecans (OCD) lesions of the free thoracic vertebrae
• OCD is a common background lesion in broiler chickens; OCD lesions are thought to require a cleft in the articular cartilage of the free thoracic vertebrae to facilitate E. cecorum colonization 
• With vertebral osteomyelitis, the most common sequela is pathologic fracture and collapse of affected vertebrae with dorsal displacement of pus and necrotic bone into the spinal canal à sudden onset of neurologic signs 
• Bacterial infection of bone > inflammatory response with edema and suppuration > TNF-a, IL-1, IL-6, PGE2 > osteoclast activation -> bone resorption
• Vertical transmission has NOT been definitively demonstrated (Borst et al, Vet Pathol, 2017). 

 

typical Clinical findings:

• Typical presentation of symmetrical hind limb paraparesis or paralysis – “hock sitting”, lameness, reluctance to walk
• Develops in affected birds at 5–8 weeks of age; results in 5%–15% mortality
  1. Increases in mortality and morbidity occur due to septicemia at 2–3 wk of age
• Paralysis results from compression of the thoracolumbar spinal cord by the inflammatory mass due to uncontrolled infection of the free thoracic vertebrae 

 

typical Gross findings:

• Soft, gray, or yellow caseous exudates often extending to spinal canal and adjacent vertebrae, resulting in medullary compression 
• If severe and disks are destroyed, fibrous replacement of disks and formation of vertebral osteophytes can occur late in the disease course (can be confused with ventral bridging spondylosis)
• May have concurrent meningomyelitis if infection has spread dorsally into spinal canal. 
• If infection has spread laterally, can see caseous abscesses around vertebrae.

 

typical light MICROSCOPIC findings:

• Acute infections: Suppurative inflammation, hemorrhage, and necrosis of intervertebral tissues and adjacent vertebrae with presence of bacterial colonies, excessive osteoclastic resorption of trabeculae
• Chronic infections: Mostly vascular connective tissue infiltrated with mononuclear cells or a mixed inflammatory population; necrotic debris in marrow spaces, thick granulation tissue surrounding large areas of necrotic bone with prominent osteoclastic activity at the margins
• +/- evidence of various stages of OCD 

 

ADDITIONAL DIAGNOSTIC TESTS:

• Culture and A/S – Enterococci are known to be resistant to several antimicrobials, so culture with antimicrobial sensitivity is highly recommended 
• PCR
• Cytology: Appear as individual cocci or diplococci 

 

Differential diagnosis:

• “Kinky back” spondylolisthesis – genetically predisposed subluxation of T4 via a ventral displacement of the cranial end of T4 that results in compression of spinal cord via narrowing of the vertebral canal; occurrence is influenced by growth rate.
• Other bacterial infections - S. aureus and E. coli are most commonly isolated in osteomyelitis secondary to bacteremia; less commonly Salmonella, Yersinia, Streptococcus, Pasturella, and Arizonae Ornithobacterium rhinotracheale uncommonly causes osteomyelitis of the skull, joints, and vertebrae secondary to severe upper respiratory disease
• Mycobacterial infections – predominate in the bone marrow
• Fungal infections – Aspergillus spp, Candida spp, Cryptococcus sp., Histoplasma capsulatum 
• Neoplasia 

 

Comparative pathology:

• Certain spp of Enterococcus (primarily E. hirae and E. durans) may heavily colonize the small intestinal mucosa in young animals in a manner similar to enteropathogenic E. coli (D-B13), resulting in diarrhea. 
• Rodents: E. ratti known to diarrhea in young rats
• Pigs: E. villorum and E. porcini also cause diarrhea in piglets
  1. Spondylitis in pigs most often happens in the upper thoracic and upper lumbar regions due to bacteremia (Erysipelothrix rhusiopathiae, Trueperella pyogenes, and Staph spp. are most common; Brucella suis important cause in some geographic areas)
• Cats: E. faecalis known to cause diarrhea in kittens; also a known cause of cystitis in cats 
• Dogs: 
  1. E. durans causes diarrhea in puppies
  2. Enterococcus spp. is a commensal organism in the ear of dogs and can cause otitis. 
  3. Spondylitis in dogs most often occurs in large males and involves the lumbosacral spine à hyperesthesia, abnormal gait, lameness
     • Staphylococcus pseudointermedius is most common cause, but Strep, Brucella canis, and E. coli have also been implicated)
     • Can also be fungal in origin (i.e. via systemic Aspergillus infection)
• Horses: 
  1. Spondylitis often involves cervical vertebrae à neck pain
  2. Can occur secondary to penetrating neck trauma or via hematogenous spread (pathogenesis unknown because IV disks are avascular in adult horses; possibly occurs via initial colonization of vascular outer annulus fibrosus, vertebral body, or end plate and extends to disk from there, but early lesions are seen centered in IV disk, so unknown)
  3. Other causes: toxoplasmosis, trypanosomiasis, experimental SIV infection
• Birds:
  1. Enterococcus faecalis is associated with tracheitis, pneumonia, and air sacculitis in canaries and finches
  2. E. hirae causes enteritis and septicemia in several species of psittacines

 

References:

1. Abdul-Aziz T, Fletcher OJ, Barns HJ, eds. Avian Histopathology. 4th ed. Madison, WI: Omnipress; 2016:78,146,325,472,478,493,513.
2. Borst LB, Suyemoto MM, Sarsour AH, Harris MC, Martin MP, Strickland JD, Oviedo EO, Barnes HJ. Pathogenesis of enterococcal spondylitis caused by Enterococcus cecorum in broiler chickens. Vet Pathol. 2017;54(1):61-73. 
3. Crespo R, Franca MS, Fenton H, Shivaprasad HL. Galliformes and Colubriformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London, UK: Academic Press; 2018:763. 
4. Dunman G, Thornton JK, Pulido-Landinez M. Characterization of an emerging Enterococcus cecorum outbreak causing severe systemic disease with concurrent leg problems in a broiler integrator in the southern United States. Avian Diseases. 2023;67:137-144.
5. Fulton RM, Boulianne M. Bacterial Diseases. In: Boulianne M ed. Avian Disease Manual. 7th ed. Madison, WI: Omnipress; 2013:179-182. 
6. Schmidt R, Reavill DR, Phalen DN. Pathology of Pet and Aviary Birds. 2nd ed. Ames, IA: John Wiley & Sons, Inc.; 2015:31,80.
7. Shivaprasad HL. Miscellaneous Diseases. In: Boulianne M ed. Avian Disease Manual. 7th ed. Madison, WI: Omnipress; 2013:385.
8. Stanton JB, Zachary JF. Mechanisms of Microbial Infections. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:191.
9. Uzal FA, Plattner BL, Hostetter JM. Alimentary System. In: Maxie MG, ed. Jubb, Kennedy & Palmer's Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Elsevier; 2016:198. 

 

 

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