Surveillance for ovine Johne's disease in New South Wales update to 31 December 1998

Johne's Disease in sheep (OJD) was first diagnosed in New South Wales in 1980. An intensive surveillance program was carried out during 1998 to better define the distribution and prevalence of the disease. This testing concentrated on investigation of flocks identified by tracing from known infected flocks, testing of identified "at risk" flocks in potential protected and control zones and subsidised testing for entry of necks into a market assurance program. More than 265,000 animals involving 1,600 submissions derived from about 1,200 properties (including 25 goat flocks with 2,150 blood samples) were tested with the agar gel immunodiffusion (AGID) test between 1 April and the end of December 1998. About 0.25% of samples was AGID positive. Autopsy of 1,030 animals (gel reactors or animals in poor body condition) yielded 26% with confirmed infection based on histopathological examination. At 1 January 1999 there were 440 flocks identified in NSW with a known history of infection of which 398 were still classified as infected. There were 204 flocks first recorded as infected in 1998. A total of 223 flocks had entered into the Market Assurance Program. Tracing and testing confirmed that OJD has continued to spread in NSW, but at a reduced rate. Most of the state still remains free of known OJD cases, and the disease is predominantly found in the central and southern tablelands. There is still no evidence of any major foci of infection independent of the known endemic area.