Characterisation of the course of Mycoplasma bovis infection in naturally infected dairy herds.

Mycoplasma bovis causes bovine respiratory disease, mastitis, arthritis and otitis. The importance of M. bovis has escalated because of recent outbreaks and introductions into countries previously free of M. bovis. We characterized the course of M. bovis infection on 19 recently infected dairy farms over 24 months. Our objective was to identify diagnostic tools to assess the efficacy of control measures to assess low risk infection status on M. bovis infected farms. PCR assays and culture were used to detect M. bovis, and in-house and BioX ELISAs were used to follow antibody responses. Cows and young stock were sampled on four separate occasions, and clinical cases were sampled when they arose. On 17 farms, a few cases of clinical mastitis were detected, mostly within the first eight weeks after the index case. Antibodies detected by in-house ELISA persisted in the serum of cows at least for 1.5 years on all farms, regardless of the M. bovis infection status or signs of clinical disease or subclinical mastitis on the farm. Six out of 19 farms became low risk as the infection was resolved. Our results suggest that, for biosecurity purposes, regular monitoring should be conducted on herds by screening for M. bovis in samples from cows with clinical mastitis and calves with pneumonia, in conjunction with testing young stock by screening longitudinally collected nasal swabs for M. bovis and sequential serum samples for antibody against recombinant antigen.