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.