JPC SYSTEMIC PATHOLOGY

DIGESTIVE SYSTEM

October 2018

D-V04

 

Signalment (JPC# 2019022): BALB/c nu/nu mouse

 

HISTORY: D-V04A: This mouse died after inoculation with an infectious agent.

 

HISTOPATHOLOGIC DESCRIPTION: Liver: Multifocally and randomly affecting approximately 60% of the liver are areas of hepatocellular degeneration, necrosis, and loss. These foci of necrosis are characterized by loss of hepatic tissue and cellular architecture and replacement by eosinophilic cellular and karyorrhectic debris (lytic necrosis) and loss of differential staining and retention of hepatic architecture (coagulative necrosis) admixed with viable and degenerate neutrophils, macrophages, and lymphocytes with variable amounts of hemorrhage, fibrin, and edema. Multinucleated viral syncytial cells that contain up to 30 small, pyknotic nuclei are frequently present within the necrotic foci, which may represent endothelial and/or parenchymal syncytia. In the adjacent parenchyma, hepatocytes are swollen and often vacuolated (degeneration) and compress the adjacent sinusoids. There is multifocal indentation of the hepatic capsule overlying areas of stromal collapse, which has occurred secondary to necrosis and hepatocyte loss. Rarely viral syncytial cells are present within the tunica intima of hepatic vessels. Periportal areas are expanded by edema and there are dilated lymphatics.

 

MORPHOLOGIC DIAGNOSIS: Liver: Hepatitis, necrotizing, acute, random, multifocal, marked, with numerous viral syncytia consistent with Mouse Hepatitis Virus, BALB/c nu/nu mouse, rodent.

 

Signalment (JPC# 2316944): Mouse

 

HISTORY: D-V04B: Tissue from a quality control mouse.

 

HISTOPATHOLOGIC DESCRIPTION: 1. Duodenum: There is multifocal to coalescing blunting, fusion, and loss of villar tips, which often contain large viral syncytial cells, up to 150um diameter, with pale flocculant cytoplasm and up to 20 nuclei.

2. Lymph node: Multifocally within the paracortex there are coalescing areas of lytic necrosis with lymphocytolysis, loss of normal architecture and replacement by necrotic debris.

3. Stomach; pancreas: No significant lesions.

 

MORPHOLOGIC DIAGNOSIS: 1. Duodenum: Villar blunting, fusion and loss, diffuse, mild, with numerous epithelial syncytia consistent with Mouse Hepatitis Virus, mouse strain unspecified, rodent.

2. Lymph node: Lymphocytolysis, multifocal.

 

ETIOLOGIC DIAGNOSIS: Coronaviral hepatitis

 

CAUSE: Mouse Hepatitis Virus (MHV - murine coronavirus)

 

SYNONYM: Lethal Intestinal Virus of Infant Mice (LIVIM)

 

·      GENERAL DISCUSSION: Common, highly contagious and highly mutagenic virus that affects all ages and strains of mice; most likely mouse disease to interfere with biological responses and contaminate transplantable tumors and cell lines

·      The clinical signs in sucklings, weanlings and adult mice vary with the virus strain, tissue tropism, mouse strain and age of mice

·      Pleomorphic, enveloped, 80‑150 nm diameter RNA virus that replicates exclusively in the cytoplasm of infected cells

·      High mortality in infant mice (LIVIM), immunodeficient mice, or genetically susceptible mice; neonates protected by passive immunity

·      Divided into two biologically distinct groups:

1.    Polytropic (eg. MHV-JHM, MHV-A59, MHV-S, MHV-3) initially replicates in nasal mucosa & disseminates to other organs

·      Immunocompromised animals : Systemic disease; acute necrosis with syncytia in liver, splenic red & white pulp, GALT, thymus and bone marrow

·      Neonatal mice: Vascular-oriented necrotizing encephalitis with spongiosis and demyelination in brain stem

·      C3H mouse: Semi-susceptible

·      BALB/c & DBA/2 mice: Susceptible

·      SJL mouse: Resistant

2.    Enterotropic (MHV-S/CDC, MHV-Y, MHVR1, MHV-D) infects intestinal mucosa of terminal ileum, cecum, ascending colon & rarely disseminates

·      Neonatal mice: Severe necrotizing enterocolitis; high mortality

·      Adult mice: Minimal lesions - enterocyte syncytia in the cecum and ascending colon

·      Immunodeficient adult mice: Minimal hyperplasia in intestinal mucosa

·      Adult nude mice: Mild intestinal lesions with minimal mucosal hyperplasia; can develop a chronic hyperplastic typhlocolitis and mesenteric lymphadenopathy

·      SJL mouse: Susceptible to enterotropic

 

PATHOGENESIS:

·      Highly contagious by the oronasal route

·      Polytropic strains: Initial replication in the nasal mucosa → hematogenous or lymphatic dissemination (in susceptible strains, mice < 2 weeks old, immunocompromised mice) → 2º replication in endothelium and parenchyma of brain, liver, lymphoid organs, bone marrow and other sites → disease → immune-mediated viral clearance → by 3-4 weeks, resolution of infection or carrier state except in nude or SCID mice → progressively severe disease (unable to mount immune-mediated viral clearance)

·      Infection of adult mouse brain can occur directly via the olfactory neural pathway

·      Enterotropic strains: Selectively infect the mucosal epithelium and rarely disseminate (the severity of the disease is age-related in neonates, not immune-related; infected adult SCID and nude mice have minimal lesions)

·      Host immunity is MHV strain specific, thus recovery from one strain will protect against re-exposure to that strain, but provides little to no protection against infection from heterotypic strain

·      Innate and acquired cell mediated and humoral immunity important for controlling infection

·      T cells critical for viral clearance & recovery

·      Maternal protection against polytropic MHV is via serum IgG

·      Maternal protection against enterotropic MHV is luminal whey containing IgA or IgG

·      Zona pellucida provides effective barrier against MHV infection

 

TYPICAL CLINICAL FINDINGS:

·      Acute disease: Ruffled hair, depression, inanition, dehydration, rapid wasting, huddling, muscle tremors, dark yellow urine and reluctance to move

·      Chronic or latent infections: No signs or porencephaly, paralysis, hepatitis, encephalitis, lymph node adenopathy, vasculitis and demyelination

 

TYPICAL GROSS FINDINGS:

·      Liver: Multifocal, random necrosis (white foci)

·      Runted and jaundiced infant mice

·      Involution of lymph nodes, spleen, and thymus

·      Ascites

·      Splenomegaly, lymphadenopathy

·      +/- peritoneal hemorrhagic exudate, jaundice

·      Necrotizing enterocolitis

·      Thin-walled intestines filled with watery, yellow digesta in neonates; thickened bowel segments in weanlings and adults

·      Mucosal proliferation or hyperplasia (ascending colon and ileocecal junction in older mice)

·      Granulomatous serositis with or without hepatic/intestinal lesions found in IFN- γ receptor -/- mice & IFN- γ -/- mice

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

·      Polytropic:

·      Focal acute necrosis & syncytia of parenchymal cells & vascular endothelium of multiple organs

·      +/- focal peritonitis

·      Syncytia of pulmonary vascular endothelium common in immunodeficient mice

·      Liver: Necrotizing hepatitis, syncytial cells within necrotic foci usually only apparent in immunodeficient mice, neutrophilic and histiocytic infiltrates, hepatocellular regeneration and fibrosis

·      Bone marrow: Necrosis of hematopoietic cells, syncytial giant cells

·      CNS: Necrotizing encephalitis, meningitis, spongiosis, demyelination, syncytial giant cells

·      Spleen, red pulp: Necrotizing splenitis, syncytial giant cells

·      Lymphoid tissue: Necrosis, syncytial giant cells

·      Olfactory mucosa, nerves, bulbs & tracts of the brain: Meningoencephalitis and demyelination

·      Clin path: Pancytopenia & compensatory hematopoietic hyperplasia

·      Enterotropic: Dependent upon age of mouse

·      Terminal ileum, cecum, ascending colon

·      Villus attenuation, enterocyte syncytia (balloon cells), mucosal necrosis

·      Eosinophilic intracytoplasmic inclusion bodies

·      Syncytial cells within mesenteric lymph nodes and endothelial syncytial cells of mesenteric vessels

·      Coinfection of enterotropic MHV with bacteria (i.e. E.coli) or parasites (Spironucleus muris) common

·      Granulomatous serositis, syncytial cell-laden, MHV Ag + serosal exudate with or without hepatic/intestinal lesions found in IFN- γ receptor -/- mice & IFN- γ -/- mice; unknown whether related to polytropic or enterotropic strains

 

ULTRASTRUCTURAL FINDINGS:

·      Enveloped virus with surface peplomers that are 12-24 nm in length

 

ADDITIONAL DIAGNOSTIC TESTS:

·      Active infection via immunohistochemistry or virus isolation

·      PCR or serology

·      Bioassay methods: MAP testing or infant/nude mouse inoculation

 

DIFFERENTIAL DIAGNOSIS:

·      Gastrointestinal disease:

·      Adult mice:

·      Tyzzer’s disease (Clostridium piliformis): Intracytoplasmic bacilli; no giant cells

·      Salmonellosis (S. enteritidis, S, typhimurium): multifocal necrosis; venous thrombi; granulomatous hepatic lesions

·      Ectromelia (mouse pox; Orthopoxvirus, Poxviridae): Splenic necrosis (“tiger striping”) and skin lesions; cytoplasmic, eosinophilic inclusion bodies

·      Infant mice:

·      Epizootic Diarrhea of Infant Mice (EDIM; Rotavirus A): Less severe disease in neonatal mice; no multinucleated giant cells or endothelial changes; epithelial vacuolar degeneration in ileum and jejunum; epithelial eosinophilic intracytoplasmic inclusion bodies

·      Reovirus-3 infection (orthoreovirus; Reoviridae): Foci of hepatic necrosis and CNS lesions; also myocardial necrosis and pulmonary hemorrhages

·      Adenovirus: Intranuclear inclusion bodies

·      Salmonellosis (S. enteritidis, S, typhimurium): multifocal necrosis; venous thrombi; granulomatous hepatic lesions

·      Cytomegalovirus (MCMV): Resistant strains include B6, B10, CBA, C3H; susceptible strains are BALB/c and A; macrophage is target cell

 

·      Neurologic disease:

·      Mouse encephalomyelitis virus (MEV)

·      Lactate dehydrogenase-elevating virus (LDV) in immunosuppressed AKR, C58 mice

·      Polyoma virus (MPyV) in immunodeficient mice

COMPARATIVE PATHOLOGY:

·      Coronaviruses of other species: villus atrophy and fusion is a common microscopic lesion with enteric infection

·      Chicken: Infectious bronchitis virus (IBV): Infectious bronchitis, nephrosis, uremia

·      Turkey (Bluecomb disease virus): Infectious diarrhea

·      Pig: Transmissible gastroenteritis virus (TGE) – diarrhea/vomiting in all age groups with high piglet mortality

Porcine epidemic diarrhea virus (PEDV) – identical clinical, gross, microscopic lesions to TGE; requires PCR or IHC to distinguish from TGE

Porcine respiratory coronavirus (PRCoV) – mild respiratory disease

Porcine deltacoronavirus (PDCoV) – all age groups exhibit diarrhea/vomiting; mortality rates in nursing piglets lower than with PEDV

·      Cat: Feline infectious peritonitis (FIP) – caused by mutated form of FECV

Feline enteric coronavirus (FECV) – mild villous atrophy

·      Dog: Canine coronavirus (CCoV) – villous atrophy (D-V03)

·      Ox: Bovine coronavirus (BCoV) – diarrhea in neonatal calves; pneumonia in calves; winter dysentery in adults

·      Ferret: Ferret coronavirus (Epizootic catarrhal enteritis) – diffuse lymphocytic enteritis; villous atrophy, fusion, and blunting

·      Rat: Rat coronavirus: Sialodacryoadenitis virus (SDAV) - squamous metaplasia of serous glands (D-V05)

 

REFERENCES:

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents & Rabbits. 4th ed. Ames, IA: John Wiley & Sons, Inc.; 2016:27-31.

2. 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. St. Louis, MO: Elsevier; 2016:146-151, 529, 541-542.