Spread Of Bovine Tuberculosis Research Articles

Calculating nature: the case of badgers, bovine tuberculosis and cattle

The aim of the paper is to examine the governmentalities associated with attempts to manage nature. In particular, it assesses the role that numbers have played in rural governance. Numbers are seen as an important tool of modern government. However, like other aspects of science, their use in governing nature has been contested by other epistemologies. Drawing upon efforts to regulate the spread of bovine tuberculosis in cattle, the paper firstly examines how numbers have been used in this policy debate. Secondly, the paper outlines three epistemologies of nature — nature as numbers, nature as known and ecological nature — which have been employed in contesting government policy. Finally the paper concludes by analysing the interactions of these knowledges of nature and considering the voice of the badger in these constructions of its identity.

Behavioural Adaptation of Brushtail Possums(Trichosurus Vulpecula)to Captivity

AbstractBrushtail possums,Trichosurus vulpecula, are New Zealand's most serious vertebrate pest, facilitating the spread of bovine tuberculosis to livestock, and causing severe damage to native flora and fauna. Possum control has become a national research priority, involving the use of large numbers of captive possums. Successful adaptation of these animals to captivity is important for the welfare of the possums and for the validity of experimental results. The objective of this study was to determine, by behavioural means, the time individually caged possums required for adaptation to captivity. We used a simple behavioural measure - a possum's daily response to a caregiver at feeding (a feeding test) - to assess changes in the behaviour of possums after arrival in captivity. We also recorded changes in possum body weight throughout this period. Initially most possums ‘avoided’ the caregiver, but within 7 days more than 80 per cent of animals no longer avoided. ‘In den’ and ‘approach’ behaviour rapidly increased for the first 14 days in captivity, after which den use became less common as more possums ‘approached’ the caregiver. By day 29 of captivity, more than 80 per cent of the possums ‘approached’ the caregiver. The possums’ body weight did not change significantly during the first 14 days in captivity, but had increased significantly by day 28, and continued to increase for at least 6 weeks after capture. These data suggest that most possums adapt to captivity within 4 weeks. For the welfare of possums and the reliability of experimental results, we recommend that possums are not used in experiments until at least 4 weeks after capture.

A simulation model for the spread of bovine tuberculosis within New Zealand cattle herds

Bovine tuberculosis, caused by Mycobacterium bovis, presents a major problem to New Zealand agriculture because of the risk that it poses to export-market access. New Zealand research has focused largely on the epidemiology of the disease in wildlife reservoirs, and relatively little is known about the dynamics of the disease in cattle. This study, therefore, investigates bovine tuberculosis (Tb) dynamics within cattle herds, by construction and application of a simple simulation model of disease transmission. The model was designed firstly to estimate rates of disease transmission within herds, and secondly to identify likely consequences of changes in herd Tb-testing policies. Both deterministic and stochastic versions of the model were used to achieve these aims.The model suggests that within-herd Tb transmission does occur and contributes to the reactor rates observed under annual herd testing regimens. The mass-action disease transmission coefficient (proportion of susceptible animals infected per unit time per infectious animal, i.e. not per diseased animal or per reactor), appears to be in the order of 2.7 × 10−5 per cow per day for a typical herd of around 200 animals, resulting in a contact rate (number of potentially infectious contacts made per infectious cow per day) of about 0.0073. These are average estimates for both beef and dairy herds.Model results suggest that improving the sensitivity of the test used to diagnose bovine Tb would improve control in areas where wildlife reservoirs are absent but have little effect where they are present. Reducing the time between tests of herds on Tb-induced movement control from the current 6 months to 2 or 3 months reduces the average time a herd spends on movement control and hence national Tb prevalence. In the presence of wildlife reservoirs of infection, both the total number of tests and total reactors per unit time increase, but the extent depends on the level of external infection. In all scenarios examined, involving thousands of model runs in total, infection was invariably absent from the modelled herd by the time it was considered clear of Tb based on testing results. This suggests that the caudal fold test is a realistic measure of herd Tb status and that Tb is unlikely to persist in herds under current testing practices in the absence of anergic cattle or an external source of infection. Specificity of the caudal-fold test as used in practice was estimated to be greater than 99%.

Modelling Bovine Tuberculosis in Badgers

We use deterministic models to study the spread of bovine tuberculosis (Mycobacterium bovis) infection within badger Meles meles subpopulations. We obtain analytical results for the models and adopt an easy-to-use approach―the Logical Parameter Search (LPS) Method―to generate appropriate parameter values for the model equations. We compare our computer-generated model parameter values with those obtained from the literature and present numerical simulations for the model system, some of which mimic the observed cyclic trend in disease incidence and prevalence as suggested, for example, by Cheeseman et al. (1989)

Electric Fences and Poison Buffers as Barriers to Movements and Dispersal of Brushtail Possums (Trichosurus Vulpecula) on Farmland.

Limitation of the spread of bovine tuberculosis by brushtail possums (Trichosurus vulpecula) in New Zealand involves creating buffer zones 3-5km wide around areas where the disease is endemic in possum populations; low possum density is established by aerial and ground poisoning and maintained by repeated control. The effectiveness of a buffer zone was examined using live-trapping and radiotracking to study movements and dispersal of juvenile and adult possums in comparison with a nearby, undisturbed (control) site. At a third site, the effect of a 3-km long, 9-strand electric fence, erected from ridge to ridge across a valley catchment, for reducing possum dispersal was measured, as an alternative to a buffer zone. Adult possums were highly sedentary; only one permanent shift of more than 0.5km was detected during repeated live-trapping and radio-tracking, and most consecutive live captures were in traps less than 200m apart. None of the radio-tagged adults adjacent to the poison buffer zones moved permanently into the low-density areas. By contrast, about 20% of radio-tagged juveniles dispersed more than 0.5km, moving up to 11.6km from their natal areas, most in a generally west-north-west to east-north-east direction. About equal numbers dispersed upstream, downstream, or in other directions. Significantly more males dispersed than females, but their dispersal distances were similar. Some dispersing possums moved more than 2km overnight, and females, particularly, often made several moves before settling. Most juveniles dispersed before they were one year old, mainly in the three months immediately preceding the peak of births in autumn. Neither the poison buffer zone nor the electric fence appeared to influence the proportion of juveniles that dispersed more than 0.5km, or the average distance dispersed. The implications of these findings in preventing the spread of bovine tuberculosis are discussed.

Studies on the spread of bovine tuberculosis from badgers to cattle

Studies on the spread of bovine tuberculosis from badgers to cattle

Restricting the movements of brushtail possums (Trichosurus vulpecula) on farmland with electric fencing

A trial was conducted to test whether an electric fence would limit local movements of brushtail possums (Trichosurus vulpecula) on farmland in the central North I. of New Zealand. If effective, such a system could be used to reduce possum and cattle interactions and the spread of bovine tuberculosis. A 3-km-long, 9-strand electric fence was erected from ridge to ridge across a valley catchment of about 160 ha. Possums were live-trapped and released at bush patches within the study area and in open areas immediately adjacent to the electric fence. Only about 30% of possums caught at local bush patches were ever retrapped at the fence, and most were caught only once at the fence. About a third of possums caught at the fence were trapped at least once on both sides of the fence. The electric fence reduced possum movements through the fenced area by about 60-80%. Most possums trapped at the fence had come from bush patches within 200 m of the fence. When the fence was switched off, possum captures on the outside increased rapidly. The effectiveness of the fence was reduced because of frequent voltage reduction by earthing from a wide variety of causes, and because possums learned to move around the ends of the fence and the fences along the farm roads. Improvements to fence design are discussed.

A Retrospective Assessment of Human Health Protection Benefits from Removal of Tuberculous Beef

In the early 1900s, government agencies instituted two programs, Federal slaughterhouse inspection and on-farm tuberculin testing, to control the spread of bovine tuberculosis (TB). From this historical perspective, the economic benefits of these programs are estimated using four parameters: (a) an estimation of how many cattle would have had bovine TB without the programs, (b) the likelihood of those infected cattle causing human illness through aerosol contamination, penetration of the skin via cuts and nicks, cross-contamination of other foods in the home, and consumption of meat and meat products, (c) current costs of treating human cases of TB, and (d) the evaluation of the benefits of preventing the death of some individuals. Based on these four parameters, the TB control programs have possible estimated economic benefits which range from $30 to $300 million annually.

Field Experiment with BCG Vaccine in Malawi

A field trial to determine the value of BCG vaccine as a means of reducing the incidence and spread of bovine tuberculosis was carried out over a period of five years with Malawi Zebu cattle kept under village conditions. 204 cattle were vaccinated twice as young calves; 210 cattle acted as controls. The cattle were physically checked and tuberculin tested at regular intervals throughout the experimental period. The cattle were slaughtered and examined post mortem. Bacteriological samples were taken from all animals. The results of the tuberculin testing and of the post-mortem and bacteriological examinations showed no significant differences between the vaccinated and control cattle. The possibility of the vaccine having a beneficial effect in preventing the progression of the disease was also investigated, but there was no significant difference between the two groups. Previous experiments on the use of BCG vaccine in cattle are discussed and it is concluded that the vaccine has no preventive effect against infection with Mycobacterium bovis, Afro-Asian strain.