Which organism is the etiologic agent of chronic respiratory disease in rodents?

• A. Mycoplasma pulmonis
• B. Staphylococcus aureus
• C. Klebsiella pneumoniae
• D. Pasteurella multocida

Answer: (A)

Chronic respiratory disease in rodents is most characteristically caused by Mycoplasma pulmonis, a wall-less bacterium that leads to murine respiratory mycoplasmosis. This organism colonizes the nasal passages and upper airways of mice and rats and often establishes a persistent infection that can progress to bronchitis and pneumonia, producing long-standing sneezing, nasal and ocular discharge, and reduced overall condition. Its lack of a cell wall means it does not stain with a Gram stain and it requires specialized media to culture, a distinctive diagnostic clue that helps separate it from other pathogens. Because of its high prevalence in lab colonies and pet rodents and its well-described clinical course, it is the best answer for the etiologic agent of chronic respiratory disease in rodents. The other organisms listed can cause respiratory infections in various contexts but are not the classic, defining cause of chronic rodent respiratory disease; for example, Staphylococcus aureus is primarily associated with skin and wound issues, while Klebsiella pneumoniae and Pasteurella multocida may cause pneumonia in other hosts but are not the primary, characteristic agents of chronic disease in rodents.