Salmonella in Swedish Cattle Epidemiology and aspects on control

In Sweden, all herds detected with salmonella are put under restrictions and measures aiming at eradication are required. The purpose of these studies was to provide a basis for decisions on how surveillance and control of salmonella in Swedish cattle can be made more cost-efficient. Results from a bulk milk screening were used to investigate seroprevalence of salmonella and to study associations between salmonella status and geographical location, local animal density, number of test positive neighbour herds, animal trade and herd size. Additional information on potential risk factors for salmonella was collected via a questionnaire sent to selected herds. The results confirmed a low prevalence of salmonella in Swedish dairy herds throughout the country, except for an island in the southeast (Öland). Test-positive salmonella status was associated with test-positive neighbours, with a stronger association for herds with indication of infection with the host-adapted S. Dublin, than for those with indication of infection with other serotypes. The results suggest local spread as an important component in transmission of salmonella between herds. Specific factors of importance in this local spread were not identified, suggesting that a broad biosecurity approach is needed in prevention of salmonella. Infection with S. Dublin was associated with herd size, and herd size was in turn associated with type of housing and many management factors, which might affect the persistence of salmonella in a herd. Costs for implementation of required measures in restricted herds during the years 1999-2013 were on average 0.49 million EUR per farm, with a median of 0.11 EUR, and a range of 1080 EUR to 4.44 million EUR. Larger herds and longer restriction periods were associated with higher costs. Efficiency of different sampling strategies was evaluated on herd level. The study highlights the importance of considering a herd’s risk of having salmonella when deciding on sampling strategies for different purposes, e.g. surveillance of pre-purchase testing.