Control of Bovine Tuberculosis in Endemic Countries
Lead Research Organisation:
University of Cambridge
Department Name: Veterinary Medicine
Abstract
Bovine tuberculosis (bTB) is a major disease of cattle but can affect other domesticated animals and wildlife. In addition, bTB poses a public health risk. Zoonotic tuberculosis (zTB) is tuberculosis in people caused by tuberculosis bacteria of animal origin. The World Health Organization (WHO) has estimated 147 000 new cases of human zTB annually and 12 500 deaths, but the true burden of zTB is likely to be underestimated. To achieve the WHO aim of ending global TB by 2030, zTB must be considered and addressed at the source of infection in the animal population. In cattle, bTB is a chronic disease which can cause reduced productivity in infected animals, affecting milk yield and carcass value. Furthermore, bTB is associated with substantial economic loss as a result of movement and trade restrictions, screening for infected animals and control efforts such as culling of affected animals, globally corresponding to an estimated cost of 3 billion USD annually.
Routine testing and slaughter of bTB positive cattle combined with movement restrictions on affected herds has successfully eliminated bTB from several countries. Nevertheless, despite intensive and costly test-and-slaughter programmes, the effectiveness of test-and-slaughter varies considerably between countries and bTB still persists in many places. In addition, test-and-slaughter is not economically feasible or socially acceptable in many bTB endemic countries and alternative control strategies are, therefore, required.
Vaccination provides potential to reduce economic barriers to controlling bTB and offers a solution for countries where test-and-slaughter is culturally unacceptable. The Bacille Calmette Guérin (BCG) vaccine commonly used in humans has shown promising results in experimental and natural transmission studies in cattle. However, there are two key barriers to the use of BCG in cattle. Firstly, it is unclear whether the vaccine provides protection from infection or simply reduces the rate of progression of disease in infected animals and, thus, the potential for onwards transmission. This distinction becomes vitally important in light of the second, and more important, barrier in that BCG vaccination undermines the effectiveness of the tuberculin skin test which underpins established control programs and is the international legal standard for establishing freedom of herds from infection.
To assess the potential of vaccination and other control measures, transmission of bTB within the population needs to be understood. The overall aim of my PhD research is to develop disease dynamics models to support the development of policies to accelerate the control of bTB. Models of disease transmission can provide insight into disease epidemiology by incorporating how infectious diseases spread within a population, specific population features and the impact of targeted control measures. In particular, I aim to develop a framework for analysis of natural transmission studies to evaluate the mode of action and efficacy of BCG vaccination as well as a generic framework for transmission and control of bTB to predict the impact and cost-effectiveness of alternative control strategies, including test-and-slaughter, segregation and vaccination. The work will strengthen scientific evidence base and support the development of policies to accelerate control of bovine tuberculosis (bTB) in endemic countries.
Routine testing and slaughter of bTB positive cattle combined with movement restrictions on affected herds has successfully eliminated bTB from several countries. Nevertheless, despite intensive and costly test-and-slaughter programmes, the effectiveness of test-and-slaughter varies considerably between countries and bTB still persists in many places. In addition, test-and-slaughter is not economically feasible or socially acceptable in many bTB endemic countries and alternative control strategies are, therefore, required.
Vaccination provides potential to reduce economic barriers to controlling bTB and offers a solution for countries where test-and-slaughter is culturally unacceptable. The Bacille Calmette Guérin (BCG) vaccine commonly used in humans has shown promising results in experimental and natural transmission studies in cattle. However, there are two key barriers to the use of BCG in cattle. Firstly, it is unclear whether the vaccine provides protection from infection or simply reduces the rate of progression of disease in infected animals and, thus, the potential for onwards transmission. This distinction becomes vitally important in light of the second, and more important, barrier in that BCG vaccination undermines the effectiveness of the tuberculin skin test which underpins established control programs and is the international legal standard for establishing freedom of herds from infection.
To assess the potential of vaccination and other control measures, transmission of bTB within the population needs to be understood. The overall aim of my PhD research is to develop disease dynamics models to support the development of policies to accelerate the control of bTB. Models of disease transmission can provide insight into disease epidemiology by incorporating how infectious diseases spread within a population, specific population features and the impact of targeted control measures. In particular, I aim to develop a framework for analysis of natural transmission studies to evaluate the mode of action and efficacy of BCG vaccination as well as a generic framework for transmission and control of bTB to predict the impact and cost-effectiveness of alternative control strategies, including test-and-slaughter, segregation and vaccination. The work will strengthen scientific evidence base and support the development of policies to accelerate control of bovine tuberculosis (bTB) in endemic countries.
