Eradication of caseous lymphadenitis under extensive management conditions on a Scottish hill farm

The application of a test and cull policy to control caseous lymphadenitis (CLA) in a commercial hill flock in Northern Scotland is described. A commercially available ELISA test kit (ELITEST CLA ELISA, Hyphen, France) was employed on blood samples taken at approximately three monthly intervals between November 2007 and August 2009. Following each round of testing all animals identified as seropositive or diagnosed as CLA-positive by bacteriology were culled. Additional hygiene and management measures aimed at reducing the likelihood of disease transmission were also encouraged in the flock. Initial testing in November 2007 identified a CLA seroprevalence of 10% (n = 1010). Following the described test-and-cull protocol and a controlled reduction in flock size the seroprevalence was reduced to 0.4% (n = 538) by August 2009. The flock is still monitored by regular palpation of external lymph nodes and bacteriologial examination of any purulent discharge. No external CLA lesions were diagnosed in the flock by clinical examination from July 2008 to date, however in May 2009 sub-clinical CLA was confirmed by post mortem examination in one ewe which had tested positive serologically. The role and potential benefits of serological testing as a tool in CLA eradication are discussed.