Surveillance Vol.14 No.3 1987 Tuberculosis "blowout" in Owaka valley Outbreaks of bovine tuberculosis (Tb) small feral herd for the same purpose. in South Otago have highlighted the Tb had never been encountered by role of possums in the spread of this Innes, nor had it been a problem in disease among cattle. the immediate vicinity. Pockets of possum Tb associated with cattle Tb have been found over Lesions the years in the Catlins area and, although this had been a cause for The tuberculosis problem on the frustration, no properties were pro- farm was first identified when 162 ducing large numbers of reactors. In steers were slaughtered at the local mid 1986, however, Innes Burgess, a freezing works and 23 were found to cattle farmer at Owaka (south of Bal- have visible lesions. Subsequently, on clutha) suffered a dramatic Tb break- 3 May 1986, 103 out of I1 79 cattle down in his cattle. reacted positive to routine tuberculin Innes, who took over the farm in testing, less than 12 months after 1954, had increased its carrying being tested clear. The earlier test had capacity from 30 head of cattle, 1200 involved 202 breeding cattle, using the ewes, and 300 hoggets to 1200 head of criteria laid down in the rules of the cattle, 4000 ewes, and 1000 hoggets by Tb control scheme that a maximum of 1987. 250 animals is required in surveillance His main problems during the testing. farm's early development had been Epidemiological investigation of the incursions by wild pigs at lambing problem by MAF veterinarians and time, but regular hunting and poison- livestock officers suggested Tb ing efforts had successfully countered infected possums were involved. A these. A few pigs were, however, left survey showed 12 out of 48 possums for recreational hunting. In addition, to be infected in one small (50 ha) area he released some fallow deer to form a of the farm, the winter grazing area. Continued overleaf 22 Surveillance 14 (3) Surveillance Vol.14 No.3 1987 The cattle Tb problem could not be To retain the emphasis on cattle, more on the user paying. However the solved until the possums, as the source Innes plans to maintain a programme nature of the Tb problem associated of infection, were removed. A limited of possum poisoning and trapping to with possums indicates that any control operation was therefore car- keep the situation under control. This efforts will be well rewarded. ried out to restrict the possum popula- is a major commitment, but it has the tion. This was undertaken by the local technical and moral support of MAF- Enquiries pest destruction board, assisted by Qual and the local pest destruction MAFQual and local farmers. board. Co-operation between farmers Concerns about the relationship An aerial drop of 1080 poison was and government agencies is proving between Tb in possums and cattle can made over three bushy gullies. The the most effective way of controlling be directed to Paul Livingstone, MAF- 1080 was used in preference to cya- the problem. Qual, Head Office, Wellington. The nide, as the possums in the area had In future the responsibility for such local contact for the Catlins area is become cyanide shy. There was a high control will be more in the hands of Martin Chalmers, Senior Livestock acceptance rate of 65-loo%, as estab- landowners, as the pest boards rely Officer, Balclutha. lished through acceptance-interference ground trials* conducted by livestock officers over three nights, using flavoured pellets and paste. As well, there was intensive “spit- ting”? over a much larger area than that covered by the aerial drop, to take care of ranging possums in open areas. This covered three-quarters of the property and fringes of neighbouring properties. Before the poisoning, an attempt had been made to eliminate the remaining feral pigs and fallow deer, in the eventuality that they too might be infected. The hunters employed to do this reported Tb lesions in the ani- mals they killed; and Martin Chal- mers, Senior Livestock Officer, Balclutha, obtained laboratory confir- mation of Tb for one pig and one deer. It seems that all the deer (about 15 in all) were eliminated, but there is less certainty about the pigs. Hunters were able to kill only a proportion of them, although the rest may have suc- cumbed to secondary poisoning by 1080, after eating the carcasses of ani- mals which died during the poisoning operation. No pigs have been seen since the operation. Effectiveness Results indicate the exercise has been successful in reducing the pos- sum population and reducing the source of Tb which was infecting the cattle. In the first post-breakdown test, in May 1987, 24 out of 1021 steers reacted positive to the tuberculin test, but on 30 July the breeding herd had a clear whole-herd test. Possum control is expensive and does not provide a simple or perma- nent solution. When a habitat has been depopulated, it takes only 5 years for migrating juvenile possums and their offspring to build up to the origi- nal population levels. Cattle, because of their low labour- input requirement, were the focus of Innes’ farming operation, and the idea of changing over to sheep had little appeal for him. *Acceptance-interference trials identify the percentage of bait accepted by the target animal and that interfered with by non- target animals. t‘‘Spitting” involves turning a sod upside down and placing the bait on the upturned soil. The sod can be returned to position after the operation, so burying the poison. Surveillance 14 (3) 23 .