Contagious mastitis - a reoccurring threat to Norwegian dairy production

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Streptococcus agalactiae 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 causes economic losses. The significant contribution from the Norwegian dairy cooperative (TINE SA) to this project reflects the concern of the dairy industry. The development is thought to be associated with the growing number of large free stall herds with automatic milking syst ems (AMS), but 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 animals, hygienic measures, antibiotic treatment and culling is used. However, many free stall herds are struggling to succeed. The reasons for this are not fully understood. There appears to be strain differences in the ability of S. agalactiae to p ersist, transmit and cause infection. 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 ma stitis 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 used to investigate sources and transmission of S. agalactiae. Isolates will be eva luated with respect to virulence- and antibiotic resistance genes, and isolates from animals and humans will be compared. Differences in genotypes will be correlated with their persistence, within-herd prevalence, and somatic cell counts of milk. Results from this project will be used to make efficient elimination protocols in modern bovine dairy herds.