Bovine TB: 2 - Understanding the Epidemiology of Cattle TB
2.0.1 Bovine tuberculosis (caused by the organism Mycobacterium bovis, abbreviated M. bovis) is a disease which poses a potential human health risk. It causes suffering to cattle, thousands of which are being slaughtered each year (over 6,000 in 1998), and both financial hardship and emotional distress to the farmers whose herds are affected. Despite 25 years of attempted TB control involving the removal of badgers, incidence of the disease is increasing and a new concerted approach is required. Little is known about the dynamics of the disease. In particular, there are no quantitative data to show the contribution badgers make to TB in cattle, nor whether badger culling is effective in controlling cattle TB.
2.0.2 Over the course of the year we have developed our assessment of the Krebs recommendations. We continue to align ourselves with his findings but have recommended an extended and strategically broad-based and interactive programme of research directed towards understanding the epidemiology of TB in cattle and wildlife, including consideration of factors related to cattle-to-cattle transmission which may be at play in influencing the control of the disease.
2.0.3 We emphasise that there is probably no single solution to the problem of TB in cattle. For future Government policy to have a firm scientific base, a comprehensive and objective approach must be made not only to obtain definitive information on the quantitative contribution of cattle, badgers and other wildlife species to the incidence of TB in cattle, but also to understand how the TB bacillus spreads within and between cattle, badgers and other wildlife populations.
2.0.4 Notwithstanding the long history of TB in cattle and its management, there are insufficient data available to assess the quantitative significance of factors such as husbandry, farming techniques, and exposure to reservoirs of infection in wildlife on the development and maintenance of TB in affected cattle herds. We also need to determine disease prevalence and infectivity in badgers and other wildlife and factors which influence the maintenance of infection in wildlife populations.
2.0.5 In short, we need to understand the epidemiology of TB in cattle and wildlife better. This is essential if the Government is to achieve the objective of controlling cattle TB while ensuring the co-existence of TB-free cattle with wildlife.
2.1 Questions to be addressed
2.1.1 In light of the above, we have reviewed the questions set out in paragraphs 1.6 to 1.8 of our original report, and have redefined and expanded them.
2.1.2 We conclude that formulation and evaluation of policy options demands basic information that will provide answers to the following key questions:-
A. What are the origins of infection? What proportion of TB cases in cattle is caused by:
- other cattle
- badgers
- other wildlife species.
B. What risk factors predispose cattle herds to TB outbreaks?
Various factors have been proposed as contributors to herd incidents, but no rigorous analysis has ever been carried out to identify and then assess the quantitative significance of these factors.
Such risk factors might include:
- farm husbandry (eg. livestock management, nutrition and health programmes, stocking density, source and purchases of stock, land management and cropping practises).
- TB incidents in nearby herds
- climate
- geographical features
- exposure to infection in badgers and other wildlife
- different strains of M. bovis.
C. What is the pattern and epidemiology of TB infection in badgers and other wildlife?
The distribution of TB infection in badgers and other wildlife at both national and local level is not known, and nor are the factors that influence the maintenance of infection within species and how and why this may vary between sites.
Factors affecting TB in badgers and other wildlife might include:
- abundance and social group structure
- population dynamics
- prevalence of infection
- severity of disease
- different strains of M. bovis.
D. What are the possible and most probable routes of transmission of infection to, within and between cattle herds - urine, faeces, respiratory discharge?
2.2 Addressing the questions
2.2.1 The Group recognises that the only way it can advise Ministers on the development of a science base capable of underpinning a sustainable long-term TB control policy is on the basis of a multi-faceted investigation. We believe this must include:
- a questionnaire based epidemiological survey
- the field trial
- studies into cattle pathogenesis
- a road traffic accident survey
- evaluation and analysis of existing TB data, and
- other related research.
2.2.2 The majority of these elements are now in place, including programmes aimed at wildlife ecology, ecological consequences of badger removal, estimation of badger population density and social group structure, vaccine development and molecular epidemiology. They are all interlinked and need to be pursued in parallel.
On to Chapter 3 - Epidemiological survey
Page last modified:
12 August 2003
Page published: 5 February 2003