The big five iceberg sheep diseases and the actions that are needed

摘要

An 'iceberg disease' is a term used to describe a disease which has a large number of undiagnosed cases so that what is seen clinically is a small representation of the total. In the sheep industry it is a phrase that is generally used to describe diseases that are insidious, production limiting, slow in onset and diagnostically challenging. The following have all been described as 'iceberg diseases' of sheep in UK: Maedi Visna (MV), Ovine Johnes Disease (OJD), Jaagsiekte (OPA), caseous lymphadenitis(CLA), Border Disease (BD), tuberculosis (TB) and scrapie. In a post mortem study of ewes at a fallen stock centre in the north of England, 6% were found to have OPA and a further 6% OJD (Lovatt & Strugnell 2013). A sero-prevalence study of 700 GB flocks in 2010 indicated that the average flock level prevalence of MV was 2.8%, though it was as high as 15% in some counties of England (Ritchie 2012). A study undertaken in 2000 indicated that as many as 18% of terminal sire flocks were infected with CLA (Baird et al 2004).