JPC SYSTEMIC PATHOLOGY

NERVOUS SYSTEM

April 2023

N-V07

 

SLIDE A: Signalment (JPC #1178019): Feeder pig

 

HISTORY: This was one of 193 feeder pigs from a Midwest stockyard. Slight coughing was observed in the group. Three days later 123 gilts were sick with an influenza-like disease. The signs noted were coughing, anorexia, vomiting, shaking of the head, frequent getting up and down, and convulsions. The next day, several were found dead and 20 others were sick. The findings at necropsy were edema and congestion of the lungs, pleural and pericardial effusion, epicardial petechiation, empty congested stomach, congestion of the intestine, liver, and spleen, and marked congestion of the meningeal vessels. Bacteriologic examination was negative.

 

HISTOPATHOLOGIC DESCRIPTION: Cerebellum, cerebrum, and brainstem: Multifocally affecting all sections, Purkinje cells and scattered neurons are shrunken with hypereosinophilic cytoplasm and pyknotic nuclei (necrosis) and are multifocally surrounded by nodular aggregates of glial cells (satellitosis). Rare Purkinje cells contain poorly discernible, round, 4-6 µm, oval, eosinophilic to amphophilic, homogenous, intranuclear viral inclusion bodies that marginate the chromatin. Neurons multifocally have cytoplasmic pallor and peripheralization of Nissl substance (chromatolysis). In all sections, the white and grey matter contain multifocal scattered aggregates of glial cells (glial nodules). Multifocally, Virchow-Robin spaces and to a lesser extent vessel walls are expanded by lymphocytes and plasma cells (perivascular cuffing). The leptomeninges are expanded by moderate numbers of lymphocytes, fewer histiocytes, plasma cells, hemorrhage, fibrin, and edema. 

 

MORPHOLOGIC DIAGNOSIS: Cerebellum, cerebrum, and brainstem: Meningoencephalitis, lymphoplasmacytic and histiocytic, multifocal, moderate, with neuronal necrosis, gliosis, and neuronal intranuclear viral inclusion bodies, mixed-breed, porcine.

 

Slide B: Signalment (JPC #2015639): Yearling Hereford crossbred steer

 

HISTORY: This steer exhibited hyperesthesia, pruritus, excessive salivation, ataxia, and paralysis.

 

HISTOPATHOLOGIC DESCRIPTION: Spinal cord: There is multifocal mild to moderate gliosis of the grey matter that occasionally forms nodular aggregates (glial nodules) that rarely extend minimally into the white matter. Multifocally within the grey matter, there are rare shrunken angular, hypereosinophilic neurons (necrosis) that contain poorly discernible, round, 4-6 µm, eosinophilic to amphophilic, intranuclear viral inclusion bodies. Multifocally, scattered glial cells similarly contain an intranuclear inclusion body as previously described. Multifocally within the grey and white matter, low numbers of lymphocytes and fewer plasma cells expand Virchow-Robin space (perivascular cuffing). 

 

MORPHOLOGIC DIAGNOSIS: Spinal cord: Poliomyelitis, lymphoplasmacytic, perivascular, multifocal, mild, with glial nodules, rare neuronal necrosis, and rare neuronal and glial intranuclear viral inclusion bodies, Hereford crossbred, bovine.

 

ETIOLOGIC DIAGNOSIS: Alphaherpesviral encephalitis / poliomyelitis

 

CAUSE: Suid herpesvirus-1 (SuHV-1, pseudorabies virus, PRV)

 

CONDITION: Pseudorabies

 

CONDITION SYNONYMS: Aujeszky’s disease, mad itch, porcine herpesvirus infection, infectious bulbar paralysis

 

GENERAL DISCUSSION: 

• Enveloped DNA virus; genus Varicellovirus; subfamily Alphaherpesvirinae; family Herpesviridae; OIE-listed notifiable disease
• Neurons are primary target: results in polioencephalitis or polioencephalomyelitis
• Pseudorabies is a worldwide, sporadic disease of domestic swine, except for Australia, Canada, North America, New Zealand, and some European countries
• The pig is the only natural host; virus maintained (reservoir host) in enzootic areas in domestic swine, feral swine, European wild boar, and brown rats (suspected)
  • Highly contagious, often asymptomatic in pigs
• Other species are dead end hosts (no viral shedding) with acute, fulminant disease
  • Virus is neurotropic in species other than pigs

 

PATHOGENESIS:

• Mechanism of injury: Disruption and lysis of neurons likely caused by actions of immune cells on virus-infected neurons
• Routes of natural infection in pigs:
  • Virus enters nasal/oral cavity or abraded skin via infected nasal secretions (direct, aerosol, fomites) à viral replication in epithelial cells of upper respiratory tract, tonsil, or monocytes-macrophagesà lysis of epithelium and viral shedding à invades sensory nerve endings of cranial nerves (olfactory, glossopharyngeal, trigeminal) à retrograde axonal transport to brain à neuronal infection à transsynaptic spread throughout CNS à cytotoxic T-cell response à neuronal dysfunction à lymphohistiocytic encephalitis with neuronal necrosis
  • Virus ingested à retrograde transneuronal infection
  • Via local percutaneous inoculation à centripetal invasion of local peripheral nerves à stimulation of regional sensory nerves à pruritis
  • Some evidence of venereal transmission in adult carrier boars
• Regardless of route of infection, virus is found in nasal secretions
• Can cross placenta and infect fetuses, causing abortion 
• Most adult pigs remain persistently infected and can harbor the virus in tonsils and nasopharyngeal secretions for many months after exposure; serve as latent carriers
  • Trigeminal ganglion, olfactory bulb, tonsil most common sites
• In other domestic species, pathogenesis is similar to pigs and transmission occurs via:
  • Direct or indirect contact with pigs
  • Ingestion of infected pork (usual source for dogs and cats)
• Viral envelope glycoproteins C, B, D, H, and L used to attach, fuse, and enter nerve cells
• Virulence factors: (Ren, J Vet Diagn Invest, 2018)
  • gB, gH – essential for replication
  • gE, gI, gC – contribute to virulence, not essential for replication

 

TYPICAL CLINICAL FINDINGS:

Pigs:

• Newborn domestic piglets: Very high mortality; rapidly become prostrate and die (12-24 hrs) without specific nervous signs
  1. High mortality has not been described in similar age wild suids
• Young piglets: Pyrexia, ataxia, congenital tremors, recumbency, generalized seizures, and variable respiratory signs; possibly high mortality, but can recover
• Postweaning and older pigs: Respiratory signs are a hallmark of infection, usually mild infection including fever, rhinitis, coughing (in domestic pigs, not described in boars), +/- mild generalized pruritus
• Susceptible pregnant sows: Early embryonic death, abortion, and mummified fetuses

Non-porcine species:

 

TYPICAL GROSS FINDINGS:

• No characteristic or specific gross lesions
• Piglets: Tonsillar necrosis +/- tracheal/esophageal necrosis; rhinitis with patchy epithelial necrosis is common; multiple 1-2mm hemorrhagic foci (necrosis) in the liver, spleen, lymph nodes, adrenal glands, placenta, intestines, and lungs; edematous lungs; lymphadenomegaly; meningeal congestion
• Non-porcine species: Cutaneous trauma associated with itching, pulmonary congestion, and hemorrhage in severe cases

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Reflect neurotropic and epitheliotropic nature of the virus
  • Epitheliotropic lesions most common in young, aborted, or stillborn piglets 
  • Neurotropic lesions more common in ruminants or carnivores 
• Neurotropic lesions
  1. Lesions most commonly observed in gray matter (polio-)
  2. Nonsuppurative meningoencephalomyelitis with trigeminal ganglioneuritis, lymphoplasmacytic perivascular cuffs, edema, gliosis, neuronophagia, satellitosis 
  3. Severe ganglioneuritis in paravertebral ganglia
  4. Lymphoplasmacytic inflammation with neuronal degeneration of gastric myenteric plexus 
  5. Acidophilic intranuclear inclusion bodies in neurons and astroglia
     • Pigs: Solid and amphophilic
     • Other species: Granular, small, and multiple
  6. Lesion distribution:
     • Piglets: Panencephalitis, most severe lesions in cerebral cortex, brainstem, spinal ganglia, and basal ganglia of brain
     • Other species: Lesion distribution in CNS is local to, and determined by, the route of exposure
     • Epitheliotropic lesions: Tiny areas of coagulative or lytic necrosis in liver, tonsil, spleen, lung, placenta, and adrenal glands with characteristic intranuclear inclusions; at site of cutaneous infection, acute serofibrinous inflammation, epithelial necrosis, ballooning degeneration, and rare intranuclear inclusions
     • Pulmonary lesions: Mild to severe
       1. Diffuse edema, mild cellular infiltration
       2. Necrotizing, hemorrhagic pneumonia
     • Necrotizing vasculitis
• Respiratory disease:
  1. Bronchointerstitial pneumonia with necrosis and sloughing of bronchial and bronchiolar epithelium; frequent eosinophilic intranuclear or faintly basophilic inclusions early in the disease
• Non-porcine species: Nonsuppurative encephalomyelitis with ganglioneuritis and neuronal intranuclear viral inclusions; nonspecific cutaneous lesions secondary to self-trauma

 

ULTRASTRUCTURAL FINDINGS:

 

ADDITIONAL DIAGNOSTIC TESTS:

• IHC highlights intranuclear inclusions in tonsil and brain
• Fluorescent antibody test (IFA) on frozen tissue (tonsils, liver, brain)
• ELISA (Cheng, J Vet Diagn Invest, 2021)
• qPCR
• ddPCR (Ren, J Vet Diagn Invest, 2018)
• Centrifugal microfluidic disk (CMFD) (Yuan, J Vet Diagn Invest, 2019)

 

DIFFERENTIAL DIAGNOSIS:  

Swine:

• Rabies (N-V06): Rare in pigs; perivascular cuffing, Negri bodies
• Viral encephalomyelitis of pigs/Teschen disease (Picornaviridae, teschovirus; N-V04): No gross lesions; nonsuppurative encephalomyelitis of predominantly the gray matter
• Classical swine fever (Flaviviridae, pestivirus; N-V16): Splenic infarction, hemorrhagic lymph nodes, tonsillar necrosis, renal petechial and ecchymotic hemorrhages, subcutaneous and serosal hemorrhage
• African swine fever (Asfarviridae): Vasculitis, edema, and hemorrhage 
• Bacterial: Streptococcus suis and Glaesserella parasuis (Glasser's disease)
• Salt poisoning (N-T08): Abundant eosinophils expanding the meninges and Virchow-Robin space
• Porcine hemagglutinating encephalomyelitis virus (Coronaviridae): Nonsuppurative meningoencephalomyelitis, neuronal degeneration

 

Cattle:

• Rabies (N-V06): Negri bodies in cytoplasm of Purkinje cells
• Polioencephalomalacia (N-T02b): Prominent cerebral cortical necrosis
• Lead toxicity (N-T05): Laminar cortical necrosis

 

COMPARATIVE PATHOLOGY:

Suid herpesvirus 1 in other species:

• Common domestic species are naturally susceptible; very few reports in goats and horses
  1. In species other than pigs, disease is usually fatal
• Natural infection occurs in mice, rats, various species of wildlife, and on fur farms
• Domestic and non-domestic canids: incidentally infected 
  1. A recent report of pseudorabies virus in two hunting dogs in Japan detected viral antigen in numerous nervous tissues and mononuclear cells; infection was associated with non-suppurative encephalitis in the brainstem; gross lesions included facial edema, tonsillar and meningeal congestion, incomplete splenic contraction, and blotchy hemorrhages on the pericardium and mitral valves (Izzati, J Comp Path, 2021)
• Mink: Unlike other species, microscopic features include vascular fibrinoid degeneration in the CNS, myocardium, and oropharynx
• Rabbit: Most sensitive laboratory animal; often used for virus identification via subcutaneous inoculation and subsequent development of intense local pruritus
• Guinea pig: Less susceptible, but succumb to intracerebral and intraperitoneal inoculation
• Raccoons and hyenas: Severe pruritus and self-trauma; nonsuppurative encephalitis with intranuclear eosinophilic viral inclusion bodies in neurons; myocardial, pancreatic, and lymphoid necrosis

Other Herpesviruses associated with encephalitides:  

• Equine herpesvirus-1
• Bovine herpsesvirus-1 and -5
• Canine herpesvirus
• Simian herpesvirus B (cercopithecine herpesvirus-1)
  • Fatal encephalitis in humans, rabbits, and some mice
• Human herpesvirus 1 (herpes simplex virus 1)
  • Fatal encephalitis in rabbits, New World primates

 

References:

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016: 258-259.
2. Cantile C, Youssef S. Nervous system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier; 2016: 370-372.
3. Caswell JL and Williams KJ. Respiratory System. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Elsevier; 2016: 530.
4. Cheng T, Magtoto R, et al. Detection of pseudorabies virus antibody in swine serum and oral fluid specimens using a recombinant gE glycoprotein dual-matrix indirect ELISA. J Vet Diagn Invest. 2021; 33(6): 1106-1114.
5. Church ME, Terio KA, Keel MK.  Procyonidae, Viverridae, Hyenidae, Herpestidae, Eupleridae, and Prionodontidae.  In: Terio, KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press Elsevier; 2018: 310-311.
6. Foster RA, Premanandan C. Female Reproductive System and Mammae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022: 1302-1303.
7. Izzati UZ, Kaneko Y, et al. Distribution of Pseudorabies Virus Antigen in Hunting Dogs with Concurrent Paragonimus westermani Infection. J Comp Path. 2021; 188: 44-51.
8. Keel MK, Terio KA, McAloose D.  Canidae, Ursidae, and Ailuridae.  In: Terio, KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press Elsevier; 2018: 239.
9. Martinez MAJ, Gasper DJ, Mucino MCC, Terio K. Suidae and Tayassuidae.  In:  Terio, KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press Elsevier; 2018: 211-212.
10. Miller AD, Porter BF. Nervous system. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022: 975
11. Ren M, Lin H, et al. Detection of pseudorabies virus by duplex droplet digital PCR assay. J Vet Diagn Invest. 2018; 30(1): 105-112.
12. Stanton JB, Zachary JF. Mechanisms of Microbial Infections. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed.  St. Louis, MO: Elsevier; 2022: 271-272.
13. Wachtman L, Mansfield K. Viral diseases of nonhuman primates.   In: Abee CR, Mansfield K, Tardif S, Morris T, Morris T, eds.  Nonhuman Primates in Biomedical Research.   London, UK: Academic Press; 2012: 15.
14. Williams B, Burek Huntington KA, Miller M.  Mustelids.  In:   Terio, KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press Elsevier; 2018: 293.
15. Yuan X, Lv J, et al. Multiplex detection of six swine viruses on an integrated centrifugal disk using loop-mediated isothermal amplification. J Vet Diagn Invest. 2019; 31(3): 415-425. 

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