Behavior of different bovine chlamydial agents in newborn calves

A chlamydial agent strain EBA-59-795, isolated from an aborted bovine foctus, induced clinical disease in 7-day-old calves and evoked microscopic tissue changes comparable with those seen in calves of naturally occurring abortions from which the agent was isolated. The chlamydial agent of bovine polyarthritis, strain LW-613, induced fatal infections in 24-hour-old calves following adminstration by mouth. After subcutaneous or oral administration with this strain, 7-day-old calves also became fatally infected. The tissue responses were studied and compared. The histological lesions were similar in the calves of the different experiments, but they differed in degree of severity. Calves inoculated with strain LW-613 had involvement of the serosal and synovial tissues which was not observed in calves inoculated with other strains. Foetal and newborn calves did not form group-specific chlamydial antibodies following infection. At an age of 43 to 57 days antibody formation began in infected calves. The age of the calf and the degree of virulence of the strains used were important factors in the outcome of the chlamydia-host interaction.