Murine Mycoplasmosis (Dirty Rat Disease) – NAVLE Study Guide
Overview and Clinical Importance
Murine Respiratory Mycoplasmosis (MRM), commonly called Dirty Rat Disease or Chronic Respiratory Disease (CRD), is caused by Mycoplasma pulmonis. This is the most common and important infectious disease of pet rats and mice, characterized by chronic progressive respiratory tract infection.
M. pulmonis is essentially ubiquitous in non-SPF rat populations and causes slowly developing, chronic disease that may not manifest until 2-18 months of age. The hallmark clinical sign is red tears (porphyrin staining) around the eyes and nose, along with snuffling, sneezing, and respiratory distress.
Etiology and Organism Characteristics
Mycoplasma pulmonis
- Classification: Mycoplasma (class Mollicutes)
- Unique Feature: LACKS CELL WALL (smallest free-living bacteria)
- Size: 0.2-0.3 micrometers
- Culture: Requires special mycoplasma media; slow-growing
- Antibiotic Resistance: Intrinsically resistant to beta-lactams and cell wall synthesis inhibitors
Epidemiology and Transmission
Prevalence
M. pulmonis is essentially ubiquitous in rats other than SPF laboratory stocks. Up to 90-100% of conventional pet rat colonies are infected. Mice are less commonly affected than rats.
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