NOVEL DIAGNOSTIC APPROACHES TO COMPREHENSIVELY DEFINE SALMONELLA DUBLIN TRANSMISSION DYNAMICS AND IMPROVE DISEASE CONTROL IN DAIRY CATTLE

The overarching goal of this project is to utilize novel diagnostic techniques and sample types to comprehensively define Salmonella Dublin transmission dynamics in dairy cattle, elucidate epidemiologic features ofSalmonella Dublin infection, and improve disease control. This will be achieved through the specific objectives listed below.Objective 1: Determine the dynamics of Salmonella Dublin shedding among calves with confirmed clinical disease (pneumonia or fever ≥ 104.0°F with or without respiratory signs, combined with identification of the organism). Northeastern U.S. dairy herds with a history of endemic Salmonella Dublin infection will be enrolled. Dairy calves < 4 months of age displaying clinical signs compatible with Salmonella Dublin infection will be intensively sampled over the course of their disease. Nasal swab, saliva, and fecal samples will be collected daily from the point of apparent disease onset until clinical recovery or death, up to a maximum of 5 days, for detection and isolation of Salmonella Dublin. Blood culture samples will also be collected to confirm infection.Objective 2: Estimate the duration of fecal shedding in calves following an outbreak of clinical disease and identify risk factors for carrier status among infected calves. Dairy calves with confirmed Salmonella Dublin infection and clinical disease from Objective 1 will be included, as will apparently healthy calves demonstrating seroconversion. Both groups of calves will be longitudinally sampled, and relevant data on each calf will be recorded. Fecal samples will be collected quarterly for one year, and blood samples will likewise be collected quarterly for antibody testing using a Salmonella Dublin ELISA to establish carrier status.Objective 3: Identify sources of Salmonella Dublin transmission to calves through surveillance focused on environmental reservoirs and maternity pen cows. Northeastern U.S. dairy herds with a history of endemic Salmonella Dublin infection will be longitudinally sampled. Herds with diverse methods of housing pre-weaned calves will be selected. Environmental swab samples will be collected from numerous prescribed locations on each farm, emphasizing the calf housing area and maternity pen, at the time of herd enrollment (baseline) and at 1 and 4 weeks following an outbreak of clinical disease. Similarly, fecal samples will be collected from cows in the maternity pen at these three time points.Objective 4: Determine the role of off-site heifer raising in propagating Salmonella Dublin. Heifer raisers in New York and Pennsylvania will be enrolled. Each raiser will be sampled in cross-sectional fashion, and heifers in three age categories will be targeted: at arrival (calves typically arrive at either 3-10 days of age or 6 weeks of age), 10-12 months of age, and 22 months of age prior to departing to the home farm. Blood samples will be collected from animals in each group for antibody testing using a Salmonella Dublin ELISA. In addition, fecal samples will be collected from heifers in the oldest age group and subjected to our protocol for isolating Salmonella Dublin.