Smittsom mastitt på fremmarsj i Norge

Contagious mastitis - a reoccurring threat to Norwegian dairy productionStreptococcus agalalactiae mastitis in cattle has reoccurred as a problem in Norwegian dairy herds. An accelerating increase in affected herds has been registered. The development is worrying because the disease is contagious and diminishes production profits. The significant contribution of the major Norwegian dairy cooperative (TINE SA) to this project reflects the concern of the dairy industry. It is speculated that the development is associated with the growing number of large free stall herds with automatic milking systems (AMS). Whether the risk of infection of a herd is higher because of the AMS, free stall housing, herd size, purchasing practices, or other factors is not known. For elimination of S. agalactiae from cattle herds, a system of sampling, segregation of infected animals, hygienic measures, antibiotic treatment and culling is used. However, many free stall herds are struggling to succeed. Reasons for failure to eradicate the pathogen are not fully understood, but could include the existence of extramammary bacterial sources, treatment failure or non-compliance with the eradication program. There appear to be strain differences in the ability of S. agalactiae to persist, transmit and cause infection. This may reflect metabolic differences or the presence of different virulence factors between strains. Humans can be infected with S. agalactiae, and infection can be fatal in infants. The extent of contact between human and bovine S. agalactiae populations is not known.The main objective is to reduce S. agalactiae mastitis in cattle in Norway. Screening of bulk milk will be used to estimate the prevalence and to evaluate risk factors for herd infection. A real-time PCR method will be validated and used to investigate sources and transmission of S. agalactiae in positive dairy herds to expose reasons for failure to eliminate the pathogen. Isolates will be evaluated with respect to virulence- and antibiotic resistance genes. Differences in genotypes will be correlated with their persistence, within-herd prevalence and somatic cell counts of milk. Isolates from farmers and humans will be compared to evaluate similarities between bovine and human S. agalactiae populations. Results from this project will be used to optimize elimination protocols in modern bovine dairy herds.