Mycoplasma bovis infections in Swiss dairy cattle: a clinical investigation.

Mycoplasma bovis causes mastitis in dairy cows and is associated with pneumonia and polyarthritis in cattle. The present investigation included a retrospective case-control study to identify potential herd-level risk factors for M. bovis associated disease, and a prospective cohort study to evaluate the course of clinical disease in M. bovis infected dairy cattle herds in Switzerland. Eighteen herds with confirmed M. bovis cases were visited twice within an average interval of 75 d. One control herd with no history of clinical mycoplasmosis, matched for herd size, was randomly selected within a 10 km range for each case herd. Animal health data, production data, information on milking and feeding-management, housing and presence of potential stress- factors were collected. Composite quarter milk samples were aseptically collected from all lactating cows and 5% of all animals within each herd were sampled by nasal swabs. Organ samples of culled diseased cows were collected when logistically possible. All samples were analyzed by real-time polymerase chain reaction (PCR). In case herds, incidence risk of pneumonia, arthritis and clinical mastitis prior to the first visit and incidence rates of clinical mastitis and clinical pneumonia between the two visits was estimated. Logistic regression was used to identify potential herd-level risk factors for M. bovis infection. In case herds, incidence risk of M. bovis mastitis prior to the first visit ranged from 2 to 15%, whereas 2 to 35% of the cows suffered from clinical pneumonia within the 12 months prior to the first herd visit. The incidence rates of mycoplasmal mastitis and clinical pneumonia between the two herd visits were low in case herds (0-0.1 per animal year at risk and 0.1-0.6 per animal year at risk, respectively). In the retrospective-case-control study high mean milk production, appropriate stimulation until milk-let-down, fore-stripping, animal movements (cattle shows and trade), presence of stress-factors, and use of a specific brand of milking equipment, were identified as potential herd-level risk factors. The prospective cohort study revealed a decreased incidence of clinical disease within three months and prolonged colonization of the nasal cavity by M. bovis in young stock.

Herd-specific strains of Mycoplasma bovis in outbreaks of mycoplasmal mastitis and pneumonia.

Mycoplasma bovis causes severe economic losses in livestock production, particularly on the Northern American continent and more recently also in continental Europe. The aim of the current study was to evaluate whether the recently emerging outbreaks were due to a particular clone or strain of M. bovis or whether these outbreaks are due to multiple infectious strains of M. bovis. The study is based on the analysis M. bovis isolated from cattle of herds with outbreaks of mycoplasmal mastitis or pneumonia from geographically non related parts of Switzerland. M. bovis isolates were typed by insertion sequence (IS) element analysis based upon ISMbov1 and ISMbov2 southern-blot hybridization. We observed a strong divergence of M. bovis strains among affected herds which mostly were herd specific. This argues against the assumption that a recent infiltration of a particular clone of M. bovis is the cause of the perilous emerging outbreaks. The study suggests that transmission occurs from animal to animal most probably via milk.