THE SPREAD OF CORYNEBACTERIUM-PSEUDOTUBERCULOSIS INFECTION TO UNVACCINATED AND VACCINATED SHEEP

The decrease in the prevalence of Corynebacterium pseudotuberculosis a fter two generations of vaccination against the disease it causes, was used to estimate the rate of control of caseous lymphadenitis (CLA), Three groups of 150 sheep, of which 50 in each group were artificially infected with C pseudotuberculosis and 100 in each group were uninfec ted sheep, were run separately for 40 months and shorn 5 times to prom ote the spread of CLA. One lot of 50 infected sheep and 2 lots of 100 uninfected sheep were vaccinated against CLA. The rate of spread of CL A was recorded. Sheep vaccinated against CLA and naturally exposed to infection had a 74% lower infection rate than unvaccinated sheep, Shee p vaccinated against CLA and exposed to only vaccinated infected sheep had a 97% lower infection rate. Unvaccinated sheep had a 76% infectio n rate, with 77% of the transmission occurring at the 4th and 5th shea rings, without any discharging CLA abscesses being observed, This stud y supports the view that in Australian wool producing flocks, CLA spre ads mainly from sheep with discharging lung abscesses to sheep with sh earing cuts, Vaccinated sheep infected with CLA have 96% fewer lung ab scesses compared with unvaccinated infected sheep and are therefore le ss likely to spread this disease to other sheep.