NAVLE Rats-Mice

Ectromelia Virus (Mousepox) – NAVLE Study Guide

March 28, 2026 18 min read 19 views
Ectromelia virus (also called mousepox) is a highly contagious viral disease affecting mice, caused by an orthopoxvirus in the family Poxviridae.

Overview and Clinical Importance

Ectromelia virus (also called mousepox) is a highly contagious viral disease affecting mice, caused by an orthopoxvirus in the family Poxviridae. While rare in modern research facilities due to strict biosecurity, ectromelia remains an important disease for the NAVLE because of its devastating impact on mouse colonies and its potential to confound research results.

Ectromelia is species-specific to mice and does not naturally infect other rodent species or humans. The disease can present in multiple forms ranging from subclinical to acute fatal depending on mouse strain, virus virulence, and immune status.

Route Mechanism Significance
Direct contact Skin abrasions, scratches, bites; contact with infected animals Primary route in colony outbreaks
Fomites Contaminated bedding, cages, equipment; virus survives in dried scabs Major source of facility contamination
Aerosol Inhalation of virus from respiratory secretions or contaminated dust Can cause respiratory form
Oral Ingestion of contaminated food, water, bedding Less common route
Vertical Transplacental or during parturition Infected dams can transmit to offspring

Etiology and Viral Characteristics

Viral Classification

  • Family: Poxviridae
  • Genus: Orthopoxvirus (same genus as smallpox, vaccinia, cowpox)
  • Genome: Double-stranded DNA virus
  • Morphology: Brick-shaped or ovoid virion, 200-400 nm
  • Replication: Cytoplasmic replication (unique among DNA viruses)

Environmental Stability

  • Highly stable in environment; can survive in dried scabs and bedding for months
  • Resistant to desiccation and many disinfectants
  • Susceptible to: Bleach (10% solution), phenolic disinfectants, formaldehyde, autoclaving
NAVLE TipRemember: Ectromelia = Orthopoxvirus = DNA virus. On the NAVLE, if you see 'brick-shaped virion with cytoplasmic inclusion bodies in mouse skin,' think ectromelia!
Form Clinical Signs Mouse Strain/Outcome
Subclinical No obvious clinical signs; may have minor tail or limb swelling; transient weight loss Resistant strains (C57BL); seroconversion without disease; chronic shedding possible
Cutaneous/Papular Maculopapular rash on tail, limbs, face, ears Progresses to pustules, ulcers, scabs Conjunctivitis, facial swelling Lymphadenopathy Moderately susceptible strains; survival common; scarring and depigmentation after recovery
Footpad/Limb Severe swelling of one or more limbs (especially hindlimbs) Footpad ulceration and necrosis Lameness, reluctance to move Possible gangrene and autoamputation Classic presentation in outbreaks; variable severity
Acute Systemic Sudden death with minimal skin lesions Lethargy, hunched posture, ruffled fur Diarrhea, weight loss Death in 7-14 days Highly susceptible strains (BALB/c, A, DBA/2); high mortality (greater than 90%)

Epidemiology and Transmission

Host Specificity

Ectromelia virus naturally infects ONLY mice. It does not cause disease in rats, humans, or other species under normal circumstances. Susceptibility varies by mouse strain:

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