Pneumonia in Rats and Mice – NAVLE Study Guide

Pneumonia in Rats and Mice

Overview

Pneumonia is a common and clinically significant respiratory disease in both rats and mice, caused by bacterial, viral, or mixed infections. The most important pathogens include Mycoplasma pulmonis (covered separately), Sendai virus (parainfluenza virus type 1), Streptococcus pneumoniae, and Pasteurella pneumotropica (now reclassified as Rodentibacter spp.). Pneumonia often results from complex interactions between multiple pathogens, with primary viral infections predisposing animals to secondary bacterial pneumonia. Clinical signs range from subclinical colonization to severe dyspnea and death, particularly in young, immunocompromised, or genetically manipulated animals. Understanding the specific pathogens, their interactions, and appropriate diagnostic and treatment strategies is essential for the NAVLE and clinical veterinary practice.

Major Pathogens Causing Pneumonia

Key Point: Severe respiratory disease in rats is typically M. pulmonis combined with Sendai virus and/or CAR bacillus. In mice, combined Sendai virus and M. pulmonis infections cause the most severe outbreaks.

Sendai Virus

Etiology and Significance

Sendai virus (SeV) is a murine parainfluenza virus type 1 that is endemic in many rodent colonies worldwide and is currently believed to be the leading cause of pneumonia in mice. It is largely non-cytolytic and selectively infects respiratory epithelium in the nose, trachea, and bronchioles, as well as type II pneumocytes. The virus is highly contagious and spreads rapidly through aerosol transmission.