THE USE OF SIMULATION MODELLING IN THE MANAGEMENT OF BRUCELLOSIS ERADICATION

Problems faced by Government veterinarians in the planning and implemention of the national bovine brucellosis eradication campaign are described. These problems stem from the uncertainty associated with the epidemiology of the disease and its initial status in eradication areas. They are compounded by contraints on abattoir capacity, finance and time. A computer stimulation model is discussed which is designed to assist campaign organisers to cope with these problems. Inputs related to expected test and slaughter rates, district disease prevalence and proposed campaign intensity are entered into the model. Output from the model inlcudes distributions giving predicted testing workloads, cattle slaughtered and disease status over the course of the campaign. The operation of the model is illustrated using data from the Bangalow district of New South Wales.     

THE EFFECT OF CALFHOOD VACCINATION WITH STRAIN 19 ON THE SEROLOGICAL DIAGNOSIS AND ERADICATION OF BOVINE BRUCELLOSIS

Data from 42,224 cattle from 694 herds collected during the brucellosis eradication campaign were used to examine the effects of calfhood strain 19 vaccination. The prevalence of infection in vaccinated herds was 1.8% compared with 9.1% in non-vaccinated herds (p< 0.005). The mean titre in the former group was lower (p< 0.001). Vaccinated herds required 3.3 herd tests to achieve a provisionally free status compared with 4.8 in non-vaccinated herds (0.001 < p < 0.005). Vaccination did not significantly reduce the number of herd tests in herds with less than 100 breeding females. In tests after the initial herd test only 0.5% reactors were found in vaccinated herds compared with 6.9% in non-vaccinated herds (p< 0.005). There were 0.9% false positive to the Rose Bengal plate test in non-vaccinated and 2.1% in vaccinated animals (p< 0.005) in non-infected herds. In infected herds this percentage was 3.0% and 4.2% respectively by (p< 0.05). In the non-infected herds there were 0.04% false positives to the complement fixation test out of 10,506 non-vaccinated cattle tested and 0.2% out of 24,734 vaccinated cattle.     

ERADICATION OF TUBERCULOSIS FROM AN EXTENSIVELY MANAGED BEEF HERD

SUMMARY Eradication of tuberculosis from a herd of 5,000 head of beef cattle with a long history of infection was achieved in a 5-year period using the single caudal fold tuberculin test in conjunction with segregation of breeders of different ages and selective slaughter of problem groups. The major problem which had to be overcome to achieve eradication was the occurrence of anergic tuberculous animals. All animals in the group were slaughtered when it was apparent testing was not successful. Testing was very effective in elminating TB from cattle under the age of two years. Incomplete musters and breakdown of segregation caused reinfection of clean groups in the early stages.