The role of wildlife inMycobacterium bovisinfection of livestock in New Zealand

Toward eradication: the effect of Mycobacterium bovis infection in wildlife on the evolution and future direction of bovine tuberculosis management in New Zealand

New Zealand's bovine tuberculosis (TB) control programme has greatly reduced the burden of tuberculosis on the farming industry, from 11% of mature cattle found with TB at slaughter in 1905 to <0.003% in 2012/13. New Zealand implemented TB control measures in cattle from the mid-twentieth century, and later in farmed deer. Control was based on established methods of tuberculin testing of herds, slaughter of suspect cases, and livestock movement control. Unexplained regional control failures and serious disease outbreaks were eventually linked to wildlife-vectored infection from the introduced Australian brushtail possum (Trichosurus vulpecula), which also triggered a wildlife disease complex involving a range of introduced species. This paper reviews the progressive elucidation of the epidemiology of Mycobacterium bovis in New Zealand's wildlife and farmed livestock, and the parallel development of research-led, multi-faceted TB control strategies required to protect New Zealand's livestock industries from damaging infection levels. The adoption of coordinated national pest management strategies, with increasingly ambitious objectives agreed between government and industry funders, has driven a costly but very successful management regime targeted at controlling TB in the possum maintenance host. This success has led to initiation of a strategy designed to eradicate TB from New Zealand's livestock and wildlife, which is considered a realistic long-term prospect.

A strategic approach to eradication of bovine TB from wildlife in New Zealand

A review and amendment of New Zealand's National Pest Management Strategy for bovine tuberculosis (TB) has led to adoption of new strategy objectives for localized eradication of disease from the principal wildlife maintenance host and infecting vector for farmed cattle and deer, the brushtail possum Trichosurus vulpecula. Historic programmes have been based on management of disease within herds and control of wildlife directed towards reducing infected herd prevalence. From July 2011, the TB strategy has been redirected towards eradication of TB from possums and other wildlife over a total area of at least 2.5 million hectares over a 15-year period. The amended strategy is intended to provide large-scale proof of concept, using two extensive bush areas, that TB can be eradicated from wildlife in New Zealand in the longer term, leading to eventual savings in control programmes needed to protect cattle and deer herds from infection. Achievement of strategy objectives will be supported by major research together with technical and managerial improvements in wildlife TB control and surveillance, and these are reviewed.

Emerging Zoonoses in Domesticated Livestock of Southeast Asia

Southeast Asia, identified as one of the hotspot for emerging and reemerging diseases is an area of emerging market with doubling population size within the next few years. The livestock industry is growing rapidly to cater for the population need via intensification and various diversification methods. This article discusses a few relevant emerging and emerging zoonoses within the past two decades and highlights the impact of these diseases to the animal industry and public health in the region.

Tuberculosis: a reemerging disease at the interface of domestic animals and wildlife

Complex interactions involving humans, domestic animals, and wildlife create environments favorable to the emergence of new diseases. Today, reservoirs of Mycobacterium bovis, the causative agent of tuberculosis in animals and a serious zoonosis, exist in wildlife. The presence of these wildlife reservoirs is the direct result of spillover from domestic livestock in combination with anthropogenic factors such as translocation of wildlife, supplemental feeding of wildlife and wildlife populations reaching densities beyond normal habitat carrying capacities. As many countries attempt to eradicate M. bovis from domestic livestock, efforts are impeded by spillback from wildlife reservoirs. It will not be possible to eradicate M. bovis from livestock until transmission between wildlife and domestic animals is halted. Such an endeavor will require a collaborative effort between agricultural, wildlife, environmental and political interests.

A descriptive spatial analysis of bovine tuberculosis in intensively controlled cattle farms in New Zealand

We describe the temporal and geographical distribution of confirmed cases of bovine tuberculosis (TB) in a population of cattle in the south-east of the North Island of New Zealand. Data were derived from routine TB testing conducted between 1980 and 2003 and included details for 69 farms. Four six-year periods were defined to coincide with changes in depopulation strategies against the wildlife TB reservoir, the brushtail possum Trichosurus vulpecula. For the periods 1980 to 1985 and 1986 to 1991 the median annual incidence rate of TB was 0.4 and 4.7 cases per 1000 cattle-years at risk, respectively. For the period 1992 to 2003 the median annual incidence rate of TB decreased to 1.8 cases per 1000 cattle-years at risk, coincident with the use of poisoning to control possums in the surrounding forest park (a major possum habitat area). We identified clusters of TB cases adjacent to the forest park and found no evidence of spatio-temporal interaction of TB risk among farms. Our findings support the hypothesis that possums living in the forest park are a source of bovine TB in this area and that farm-to-farm spread of disease was not an important infection mechanism.

Advances in understanding disease epidemiology and implications for control and eradication of tuberculosis in livestock: the experience from New Zealand

A deteriorating tuberculosis problem in cattle and deer in New Zealand has been halted and then reversed over the last decade. Mycobacterium bovis infection in both wild and domestic animal populations has been controlled. This has been achieved by applying a multi-faceted science-based programme. Key features of this have been a comprehensive understanding of the epidemiology of tuberculosis in animals, confidence in sampling wild animal populations, effective application of diagnostic tests in cattle and deer, and the ability to map M. bovis genotypes.

A new method for estimating the effort required to control an infectious disease

We propose a new threshold quantity for the analysis of the epidemiology of infectious diseases. The quantity is similar in concept to the familiar basic reproduction ratio, R0, but it singles out particular host types instead of providing a criterion that is uniform for all host types. Using this methodology we are able to identify the long-term effects of disease-control strategies for particular subgroups of the population, to estimate the level of control necessary when targeting control effort at a subset of host types, and to identify host types that constitute a reservoir of infection. These insights cannot be obtained by using R0 alone.

Control and eradication of animal diseases in New Zealand

New Zealand is free from all the major epidemic (Office International des Epizooties List A) diseases of animals and other important diseases, such as rabies and the transmissible spongiform encephalopathies. The once endemic conditions of sheep scab (Psoroptes ovis), bovine brucellosis (Brucella abortus), hydatids (Echinococcus granulosus) and Aujeszky's disease have been eradicated. Anthrax (Bacillus anthracis) is no longer considered endemic and Pullorum disease (Salmonella Pullorum) has effectively been eradicated from commercial poultry flocks. There are current control programmes for bovine tuberculosis (Mycobacterium bovis), enzootic bovine leucosis in dairy cattle, infectious bursal disease, ovine epididymitis (Brucella ovis), and caprine arthritis encephalitis. Historically, incursions by three important non-endemic diseases, contagious bovine pleuropneumonia, classical swine fever and scrapie, have been successfully eliminated. Any new occurrence of a serious exotic disease would be dealt with swiftly using powerful legislative authorities available for the purpose.

Veterinary epidemiology in New Zealand: a 50-year perspective

Abstract Extract The science of epidemiology is still developing although some of its principal tenets, such as identification of risk factors through comparisons of rates of disease occurrence among population sub-groups of individuals, have been used for centuries. The past 50 years has seen a particularly rapid period of growth of the discipline that has become almost exponential, especially since microcomputers and powerful analytical programs became widely available in the 1980s. The most outstanding advance has arguably been the development of causal criteria that arose from the fierce debate about links between smoking and lung cancer. The philosophical concepts of associations between cause and effect that are embodied in causal criteria now underpin epidemiological practice for scientific evaluation of evidence.