Xishan Biology

Introduction to Pathogens

Respiratory ciliary bacterium

CAR bacillus disease (Cilia-associated respiratory bacillus infection) is a typical respiratory illness affecting various animals, caused by the Cilia-associated respiratory bacillus. It was first isolated in 1980 from the lungs of rats infected with pneumonia. Rodents infected with this bacterium typically exhibit symptoms such as weight loss, disheveled fur, teeth-chattering, or wheezing. Almost all affected animals develop mucous-filled bronchitis and chronic bronchiectasis. To date, no human infections have been reported. According to testing data from 2020 to 2023 provided by Suzhou Xishan Bio, a third-party testing institution in China, the positive rate for respiratory cilia bacilli among laboratory animals was 0%.

Pathogenic Characteristics

 

CAR bacilli are Gram-negative, filamentous bacteria that are motile, moving via a "gliding" mechanism. During locomotion, they adhere to solid surfaces and propel themselves by bending their bodies. These bacteria measure 4–6 μm in length and do not form spores. CAR bacilli can be cultured in serum-containing cell culture media as well as in chicken embryo allantoic fluid, and they require 7% CO₂ for optimal growth. The bacteria can be inactivated at 56°C for 30 minutes, yet remain infectious when stored in urine at 23°C for up to one week. They are also highly resistant to repeated freeze-thaw cycles and can be effectively preserved at -70°C. Currently, researchers have conducted homology analyses of the 16S rRNA gene from CAR bacilli isolated from different sources. The results reveal that strains derived from rats and mice exhibit remarkably high similarity, whereas those from rabbits show significant divergence. Specifically, the 16S rRNA sequence from rat-derived CAR bacilli shares 83% identity with *Rhodococcus roseus*, 83% with *Chitinophaga pinensis*, and 81% with *Curvibacter sancti*. These findings provide valuable insights for the taxonomic classification of CAR bacilli.

There is obvious infiltration of round cells around the mucosa and bronchi, with neutrophil exudation observed within the airways. The ciliary body margins are densely packed, and colonization by CAR bacilli can be seen.

Epidemiology

 

The primary mode of transmission is direct contact. If the mother is a carrier, animals may become infected as early as one week after birth. Since this bacterium spreads through direct contact, sentinel animals are not effective in detecting it, and thus the possibility of transmission within the population remains unresolved.

Infecting rats with tracheal lavage fluid from infected rats or by inoculating rat and mouse nasal passages with chick embryo passaged material can reproduce lesions similar to those observed in natural cases. When experimentally healthy rats are housed together with infected ones, the disease can be transmitted. The primary route of infection is likely through respiratory transmission. Once established, the pathogen is typically difficult to eliminate from the respiratory tract, allowing infected rats to remain a persistent source of infection for an extended period.

Clinical symptoms and pathological changes

 

Among all susceptible animals, infections are predominantly latent. When clinical symptoms do appear, they typically involve chronic infections and classic respiratory diseases, accompanied by weight loss, disheveled fur, teeth-chattering, or hissing sounds. In rats, bloody tears may also occur. Rats exhibit more severe clinical signs compared to mice; in fact, the symptoms observed in rats infected with CAR bacillus closely resemble the respiratory symptoms associated with Mycoplasma infection.

Similar to Sendai virus disease and mycoplasmosis, this condition has a relatively long incubation period. The characteristic clinical sign is an abnormal "gurgling" respiratory sound. Some rats exhibit arching of the back and difficulty breathing. Excessive amounts of clear or milky-white mucus accumulate in the trachea, while the lungs show incomplete collapse. Additionally, cervical lymph nodes appear hemorrhagic, with evidence of atelectasis and swelling in the mandibular region. The primary pathological changes include peribronchial cell infiltration and bronchiectasis—features that closely resemble those seen in mycoplasmosis. However, distinguishing between the two diseases can be aided by the presence of plasma cell infiltration, basophilic cells in the ciliated portion of the bronchial mucosal epithelium, and mild neutrophil infiltration within the tracheal lumen.

The Impact on Research

 

Chronic respiratory diseases in laboratory rats can disrupt, impair, and even derail long-term research efforts—particularly those involving respiratory studies—since they are the leading cause of illness and mortality in conventional rodent colonies.

Prevention and Removal

 

CAR bacteria are primarily transmitted through direct contact; there is no evidence to suggest transmission via contaminants, carrier animals, or airborne aerosols. The primary preventive measure is to avoid direct contact between infected and uninfected animals. Animal populations should undergo regular screening for CAR bacteria, and newly introduced animals must be quarantined to rule out infection. The emergence of this bacterium in previously unaffected groups indicates the introduction of infected animals—possibly from wild sources—and calls for a careful reassessment of disease-control strategies. In infected populations, CAR bacteria spread relatively slowly. While restricting animal movement and using PCR and serological tests can help track infected individuals, it is still recommended to either reintroduce animals from disease-free sources or implement pathogen-free management protocols. Pathogen-free management can be achieved through cesarean sections or embryo transplantation.

References

 

1. Li Qiaofan. Advances in Research on a Novel Respiratory Pathogen of Laboratory Animals: Respiratory Ciliary Bacillus

2. James R. Ganaway et al. Pathogens of Chronic Respiratory Diseases: Isolation, Cultivation, and Characterization of Rat Ciliated Respiratory Bacilli, a Newly Recognized Pathogen

3. Laboratory Animal Epidemiology

 

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