Cilia-Associated Respiratory Bacillus Infection

Cilia-associated respiratory (CAR) bacilli are widespread and significant respiratory pathogens in rats, commonly infect rabbits, and probably infect mice at a higher rate than is currently recognized.

FIG. 1.66. Respiratory mucosa of a mouse experimentally monoinfected with cilia-associated respiratory (CAR) bacillus. Note rafts of bacteria (arrows) on the epithelial brush border and within the exudate.

Experimental, and probably natural, infections may be inapparent with no discernable lesions. The organism has been associated with chronic respiratory disease in conventional B6 and B6 obese mutant mice dying with the disease. Chronic suppurative cranioventral broncho­pneumonia with marked peribronchiolar infiltration with lymphocytes and plasma cells and luminal neutro­philic exudation were evident microscopically. Warthin-Starry silver impregnation staining revealed typical filamentous CAR bacilli among cilia. Although disease can be experimentally induced by CAR bacillus monoinfection (Fig. 1.66), natural outbreaks of disease in mice seem to be associated with viral infections, including Sendai virus and PVM. Chronic respiratory disease and seroconversion have been produced in BALB/c mice inoculated intranasally with the CAR bacil­lus, but B6 mice developed less severe lesions and lower antibody responses.

Diagnosis is achieved by silver staining of respiratory tissue to reveal characteristic organisms among cilia of the respiratory epithelium. Organisms can be grown in cell cultures, cell culture medium, and embryonated hens' eggs. Serologic assays utilize bacterial lysates, which are prone to considerable nonspecificity due to cross-reactivity with other bacteria. PCR can be utilized to detect mild or subclinical infections in rodents and can be applied to nasal, oral, and tracheal swabs, with the oral cavity being the most suitable noninvasive site for detecting early infection.