JPC SYSTEMIC PATHOLOGY

NERVOUS SYSTEM

January 2023

N-B10

 

Signalment (JPC #2907779): A chick

 

HISTORY: Several chicks from this flock were recumbent and had torticollis. One bird was submitted for necropsy examination and histopathology.

 

HISTOPATHOLOGIC DESCRIPTION:  

Slide A: Cerebrum, multiple sections: Multifocally and randomly, affecting both gray and white matter, there are variably sized, up to 2 mm in diameter, areas of rarefaction characterized by increased pallor with loss of normal architecture and scattered scant cellular and karyorrhectic debris (liquefactive necrosis). These foci contain low numbers of gitter cells with abundant eosinophilic vacuolated cytoplasm and rare heterophils as well as scattered necrotic neurons characterized by shrunken, hypereosinophilic cytoplasm, and pyknotic nulcei. Within necrotic areas, small caliber blood vessels are often lined by hypertrophic endothelial cells (reactive) and are occasionally occluded by fibrin thrombi.  Multifocally within necrotic areas there are small aggregates of 1-2µm diameter basophilic cocci that are occasionally within histiocytes. At the periphery of necrotic foci, there is mild vacuolization of the neuropil and white matter parenchyma (spongiosis); few eosinophilic, swollen axons (spheroids) within dilated myelin sheaths; hypertrophied, reactive astrocytes with abundant eosinophilic cytoplasm (gemistocytes), and increased numbers of glial cells (gliosis).

 

Slide B: Brown and Brenn: Multifocally, there are few Gram-positive 1-2µm diameter cocci observed individually and in clusters within areas of rarefaction/necrosis.

 

MORPHOLOGIC DIAGNOSIS: Cerebrum: Encephalitis, necrotizing, subacute, multifocal, moderate, with gitter cells, spheroids, gliosis, and few intrahistiocytic and extracellular gram-positive cocci, chicken, avian.

 

ETIOLOGIC DIAGNOSIS: Enterococcal encephalitis

 

CAUSE: Enterococcus hirae

 

GENERAL DISCUSSION:

• Gram-positive cocci that occur singly, in pairs, or short chains; non-motile, non-spore-forming, facultative anaerobes

• Major pathogenic species are E. faecium, E. faecalis, E. cecorum, and E. hirae

• Previously classified as Lancefield group D Streptococcus spp. commonly referred to as “fecal streps”
• Enterococcus spp. are considered normal flora of the intestinal tract; opportunistic pathogens

• In chickens, E. hirae is usually only found in the small intestine of 3-4 week olds

• Enterococcus hirae is most often associated with growth depression, septicemia, endocarditis, and encephalomalacia in young poultry
• One report of osteomyelitis from E. hirae in a chicken (Kolbjornsen, Vet Pathol. 2011)

• Septicemia in psittacine birds
• Diarrhea in rats, dogs, pigs, rabbits, ruminants and horses

 

TYPICAL CLINICAL FINDINGS:

• Torticollis
• "Star-gazing"
• Lame and may be found sitting on their hocks
• May be found dead

 

TYPICAL GROSS FINDINGS:

• Pinpoint yellowish lesions on the brainstem; typically no cerebellar lesions
• Splenomegaly
• Hepatomegaly
• Renomegaly
• Endocarditis
• Fibrinous pericarditis

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Large, well demarcated foci of necrosis, predominately in the brainstem
• Gram-positive bacterial colonies are observed in thrombosed vessels and in necrotic foci
• In affected areas, only blood vessels may be preserved
• Few infiltrating heterophils

 

ADDITIONAL DIAGNOSTIC TESTS:

 

DIFFERENTIAL DIAGNOSIS:

• Vitamin E deficiency (crazy chick disease; N-M22)

• Encephalomalacia of chicks or turkey poults: Cerebellar hemorrhage (from multifocal petechiae to large areas), necrosis, demyelination, and neuronal degeneration

• The most common Streptococcus and Enterococcus spp. causing both septicemia and localized infections in poultry are:  S. zooepidemicus, S. bovis, E. hirae, E. durans, and E. faecalis

• Enterococcus cecorum (G+) is an emerging avian pathogen in broiler chickens and breeder flocks that primarily affects the free thoracic vertebra (FTV) and its articulations causing vertebral osteoarthritis (AKA enterococcal spondylitis [ES]; “kinky back”) resulting in symmetrical hind limb paraparesis or paralysis due to spinal cord compression by an inflammatory mass; proposed pathogenesis:  intestinal colonization of pathogenic E. cecorum 1-3 weeks of age > bacteremia > colonization of pre-existing OCD lesions (mechanism unknown; FTV OCD lesions common in broiler chickens during same period) > ES (Borst, Vet Pathol. 2017)

• Highly Pathogenic Avian Influenza (HPAI; D-V25)

• Brain, spleen and heart most frequently affected
• Vasculitis that is most prominent in the meninges with perivascular inflammation

• Salmonella enterica subspecies arizonae (S-B01): 

• Septicemia, neurological signs, blindness; egg-transmitted disease primarily of young turkey poults; heterophilic and fibrinous meningitis; heterophilic exudate in anterior chamber and/or vitreous (later in disease course)

• Other bacterial septicemic diseases should be considered, such as staphylococcosis, colibacillosis, pasteurellosis, and erysipelas

 

COMPARATIVE PATHOLOGY:

• Enterococcus hirae has been reported to cause (or reported in association with):

• Septicemia in psittacine birds
• Diarrhea in rats, dogs, pigs, rabbits (suckling rabbits), ruminants and horses
• Rare reports of Enterococcus spp. mastitis in dairy cattle

 

REFERENCES

1. Borst LB, Suyemoto MM, Sarsour AH, et al. Pathogenesis of enterococcal spondylitis caused by Enterococcus cecorum in broiler chickens. Vet Pathol. 2017;54(1):61-73.
2. Chadfield MS, Christensen JP, Juhl-Hanson J, Christensen H, Bisgaard M. Characterization of Enterococcus hirae outbreaks in broiler flocks demonstrating increased mortality because of septicemia and endocarditis and/or altered production parameters. Avian Disease. 2005;49:16-23.
3. Kolbjornsen O, David B, Gilhuus M. Bacterial osteomyelitis in a 3-week-old broiler chicken associated with Enterococcus hirae. Vet Pathol. 2011;48(6):1134-1137.
4. Logue, CM. Other Bacterial Diseases. In: Swayne, DE, ed. Diseases of Poultry. 14th ed. Ames, IA: John Wiley & Sons, Inc.; 2020:10006-1010.
5. Swayne, DE, Barnes HJ, Abdul-Aziz, T, Fletcher, OJ. Nervous system. In: Abdul-Aziz T, Fletcher OJ, Barnes HJ, eds. Avian Histopathology. 4th ed. Jacksonville, FL: American Association of Avian Pathologists; 2016: 513.

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