Control of caseous lymphadenitis in sheep: Risk factors for disease and validation of an interferon-gamma assay
This study investigated control of Caseous Lymphadenitis (CLA) by examining the validity of a whole blood interferon-gamma (IFN-[gamma]) enzyme immuno assay in determining disease status in naturally infected sheep. The assay, using formalin-inactivated whole bacterial cells as antigen, was assessed in known-negative, experimentally and naturally infected sheep. A sensitivity of 91% and specificity of 98% were observed when using a cut-off of 0.09 optical density (OD). Necropsy, revealed little correlation between test response and extent of infection, but did confirm the status of test negative animals. An algorithm was developed for the use of the assay in eradication of CLA. A mail survey of Ontario sheep producers determined that source of replacement stock, using a contract shearer and type of feeder are risk factors associated with abscess status of the flock (P<0.05). The IFN-[gamma] assay has the potential to be a useful tool in an eradication program for CLA.