Satoru Matsushita

Serodiagnosis of cilia-associated respiratory bacillus infection by the indirect immunofluorescence assay technique

Antibody to cilia-associated respiratory (CAR) bacillus was detected by the indirect immunofluorescence assay (IFA) technique using tracheal sections of infected mice as antigen in serum samples collected from rats infected naturally and experimentally. Nine of 23 cases of natural infection were positive in IFA antibody, with titres ranging from 1:10 to 1:80, and all these antibody-positive cases were also histologically positive. The remaining 14 cases were negative in both IFA antibody and histological diagnosis, even though some of them were infected with Sendai virus and Mycoplasma pulmonis. In the experimental infection, serum samples collected from 18 rats on days 4, 7, 14, 21, 28 and 56 post-inoculation (PI) (three rats for each point) and examined for IFA antibody revealed that seroconversion occurred in one rat on day 14 PI and in three rats on day 21 PI. Antibody titres of 1:80 to 1:160 remained to the termination of the experiment. The IFA technique was useful for the diagnosis of CAR bacillus infection except in the early stage of the infection.

Transmission experiments of cilia-associated respiratory bacillus in mice, rabbits and guineapigs

Transmission experiments of cilia-associated respiratory (CAR) bacillus were performed in mice in order to clarify the principal route of the infection, and in rabbits and guineapigs in order to examine their susceptibility. Determination of the infection was evaluated serologically by the indirect immunofluorescence assay (IFA) technique and histologically by the presence of CAR bacillus in the airways. BALB/c mice were intranasally inoculated with the SMR strain of CAR bacillus. The IFA antibody to the bacteria in these mice rose to more than 1 : 160 at 4 weeks postinoculation (PI) and the mice were utilized as transmitters for the following experiments. One out of 15 uninfected mice kept in intracage contact with infected mice became infected from 4 weeks after contact. Incidence of contact infection increased thereafter. On the other hand, there was no evidence of infection in the uninfected mice housed in the separate cages from the cage in which infected mice were housed throughout the 12-week observation period. The primary method of CAR bacillus transmission seems to be direct contact with infected mice or fomites contaminated by infected mice; airborne transmission appears to be of little importance. Rabbits and guineapigs were also intranasally inoculated with the SMR strain of CAR bacillus. IFA antibodies were positively detected by 4 weeks PI, but no CAR bacillus nor histological changes relating to the infection were observed in the airways of either species. It is suggested that rat origin CAR bacillus can transmit to rabbits and guineapigs, and that the infection can spread to other species of rodents and rabbits.

Pathology of rats intranasally inoculated with the cilia-associated respiratory bacillus

Five-week-old Wistar/Ms rats were inoculated intranasally with a lung homogenate containing a strain of cilia-associated respiratory (CAR) bacillus and were examined on days 4, 7, 14, 21, 28 and 56 postinoculation (PI). Some rats showed clinical signs with wheezing and considerable body weight loss from day 21 PI. Gross lesions, including enlargement of lungs with focal atelectasis, bronchiectasis and emphysema, were observed from day 21 PI. Histologically, round cell infiltration was first present in the lamina propria of the nasal respiratory mucosa on day 7 PI. From day 14 PI, colonization of the CAR bacillus (4-8 µm in length), associated with round cell infiltration in the lamina propria and the peripheral regions, was observed in the ciliated mucosa of the bronchioles, bronchi, trachea and nasal cavities. Generally, the lesions progressed and expanded from upper to lower airways with time. Sporadic mucopurulent bronchopneumonia was observed from day 21 PI in some rats. The CAR bacilli (0·2-0·25 µm in diameter) were also demonstrated electron-microscopically in the ciliated epithelium of the intrapulmonary airways. The CAR bacillus antigen was demonstrated on the ciliated mucosa of the affected airways by the indirect immunofluorescence assay technique. Microbiological examination revealed that the rats used in this study were free from other known respiratory pathogens throughout the experimental period. Thus, it is suggested that the CAR bacillus alone can produce a murine respiratory disease. Fourteen days were needed for pathological lesions to develop.