Arb. Higgs et Cd. Hawkins, OVINE JOHNES-DISEASE - THE RISK ASSOCIATED WITH SHEEP IMPORTED INTO WESTERN-AUSTRALIA, Australian Veterinary Journal, 76(8), 1998, pp. 546-550
Objective To assess the risk of Johne's disease not being detected in
sheep imparted from New South Wales into Western Australia. Design A s
tochastic simulation model. Procedure The process of importing sheep w
as broken down into steps and numbers or probabilities assigned to eac
h. Controls on the movement of sheep included surveillance tests in so
urce flocks and serological tests on sheep in consignments before and
after transportation to Western Australia. The model calculated the ri
sk of occurrence of Johne's disease in Western Australia and the succe
ss of the agar gel immunodiffusion test in identifying consignments wi
th infected sheep. Results Negative surveillance tests in source flock
s reduced the risk to about one twentieth of that when no surveillance
tests were required. On average, Johne's disease was predicted to be
introduced once in every 3 to 7 years when no testing of either the so
urce flock or the sheep in consignments was required. When negative su
rveillance tests only were required the interval increased to once in
every 63 to III years and, with the additional requirement that all sh
eep in each consignment must have a negative lest before and after tra
nsport, the interval further increased to once in every 125 to 333 yea
rs. When only sheep in consignments were tested, the interval was calc
ulated to be 8 to 14 years. Conclusion A requirement that imports be d
erived from flocks which had negative surveillance tests to Johne's di
sease would provide significantly greater protection for the sheep ind
ustry in Western Australia.