Mouse Hepatitis Virus (MHV) – NAVLE Study Guide

Overview and Clinical Importance

Mouse Hepatitis Virus (MHV) is a highly contagious coronavirus that is one of the most common infectious agents in laboratory mouse colonies worldwide. MHV causes a spectrum of diseases ranging from asymptomatic infection to severe hepatic necrosis, enteritis, encephalitis, and respiratory disease, depending on viral strain, mouse age, immune status, and genetics.

MHV is critical for the NAVLE because it represents the prototype murine coronavirus, shares genomic features with SARS-CoV-2, and is a major confounding variable in research. Understanding MHV strain differences and disease manifestations is essential.

Etiology and Viral Characteristics

Viral Classification

• Family: Coronaviridae
• Genus: Betacoronavirus
• Genome: Positive-sense single-stranded RNA (27-32 kb)
• Morphology: Enveloped, spherical, 80-120 nm, crown-like surface spikes
• Strains: Over 25 strains (MHV-1, MHV-3, MHV-A59, MHV-JHM, MHV-Y, etc.)

MHV Strain Classification by Tropism

Epidemiology and Transmission

• Fecal-Oral (Primary): Enterotropic strains shed in feces
• Aerosol/Respiratory: Polytropic strains shed in respiratory secretions
• Fomites: Contaminated bedding, cages, equipment; virus survives days
• Asymptomatic Carriers: Immune adults shed virus without clinical signs

Clinical Presentation by Disease Form

IMPORTANT: Most MHV infections in immunocompetent adult mice are SUBCLINICAL. Disease expression depends on strain, age, genetics, and immune status.

1. Hepatic Form (Polytropic Strains)

Most Common Presentation in Research Settings

• Clinical Signs: Often subclinical; severe cases show lethargy, hunched posture, ruffled fur
• Gross Pathology: WHITE FOCI on liver surface (pathognomonic)
• Histopathology: Focal necrotizing hepatitis with SYNCYTIAL CELLS (multinucleated giant cells)
• Outcome: Self-limiting in immunocompetent; fatal in immunodeficient

2. Enteric Form (Enterotropic Strains)

• Age: Suckling mice (less than 2 weeks old) most susceptible
• Clinical Signs: Watery diarrhea, dehydration, weight loss, high mortality in neonates
• Histopathology: Transient syncytia in intestinal mucosal epithelium, villous atrophy

3. Respiratory Form (Polytropic Strains)

• Clinical Signs: Dyspnea, nasal discharge, ruffled fur (uncommon)
• Pathology: Interstitial pneumonia, rhinitis

4. Neurologic Form (MHV-JHM Strain)

• Clinical Signs: Tremors, paralysis, ataxia, seizures
• Pathology: Acute encephalitis, chronic demyelination (used as MS model)

Diagnosis

Treatment and Management

NO specific antiviral treatment. Management focuses on colony eradication and prevention.

Colony Management

• Depopulation of infected colonies
• Thorough facility decontamination (bleach, formaldehyde)
• Restock with SPF (specific pathogen-free) mice

Prevention

• SPF sourcing, quarantine, barrier housing, sentinel monitoring