Ovine caseous lymphadenitis (CLA) and ovine Johne's disease (OJD) or paratuberculosis have been serious diseases in the Australian sheep industry, mainly causing losses from abattoir condemnations from CLA or mortalities on the farm from OJD. CLA is now a disease of minimal concern, with clinical cases reported rarely. Although OJD continues to spread through parts of the sheep population, the catastrophic losses in flocks occurring prior to the introduction of vaccination are now uncommon. Change-management factors relevant to the improvements in both prevalence and producer concerns for CLA and OJD were examined, including drivers and motivation for change, resistance to change, knowledge management, farming system dimensions and leadership. Although extension programs addressing disease risk factors are likely to be of relevance to improved knowledge and attitudes towards disease risk management of producers, improvements in disease-control practices were considered largely attributable to the introduction of vaccination programs for CLA in 1983 and OJD in 2002. Inclusion of the CLA antigen within clostridial vaccines ("6 in 1" vaccine) enabled routine annual CLA vaccination to occur in an increasing proportion of the national flock, with estimates of CLA prevalence suggesting a decline from 26% in 1995 to 5.2% in 2009. Encouraging the routine vaccination of lambs for OJD (Gudair vaccine) in infected flocks to reduce or avoid losses significantly reduced the within-flock prevaccination-postvaccination median prevalence from 2.72% to 0.72%, based on estimated shedding rates of Mycobacterium avium subsp. paratuberculosis determined by pooled fecal culture in 37 infected flocks vaccinating for at least 5 years. Although persistent use of CLA vaccine is a convenient intervention for producers, promoting the persistent use of OJD vaccination to continue disease suppression when clinical cases are undetectable, plus improvements in biosecurity, remain a challenge for animal-health authorities. Despite concerns of vaccine efficacy and safety issues with OJD vaccination, persistent vaccination has produced a profound improvement in the health of Australian sheep, and is a positive development of relevance to sheep production in other countries.
Keywords: CLA; OJD; caseous lymphadenitis; disease-control programs; ovine Johne’s disease; paratuberculosis; sheep health; vaccination.
© 2014 Windsor.