Bovine TB: Epidemiology research
Epidemiology is the study of disease patterns. Whilst occasionally a clear cause and effect relationship can be demonstrated, in most cases the situation is more complex and the research tells us what factors are important concerning a specific question or a theoretical level of risk associated with a particular event, behaviour or contact. There are many recognised branches of epidemiology, for instance there is molecular epidemiology where known genes are studied and environmental epidemiology which looks at exposure to an agent and the outcome of the exposure plus many others. All forms involve some form of mathematical or statistical analysis to look at disease patterns. Basic epidemiologic study designs use primarily observational data and are applicable to all branches of epidemiology. Studies can be organised into descriptive, cohort, case-control, cross-sectional or ecological designs which are investigation and exposure assessment tools. Often the methods employed provide population level data and so such techniques are used by Defra to help develop policy.
How does Defra decide on what research to fund?
Research is funded in order to provide evidence based policies for control of bTB. The Independent Scientific Group (ISG) on Cattle TB provides advice to the department on future research requirements. Other advice is sought from specialists within Defra and from other stakeholders and independent experts. Many of the epidemiology projects fall under a steering group where invited experts and members of the ISG give advice to Defra on the ongoing objectives of the work and help decide if a change of direction is needed.
Research projects
The spatial component of TB in cattle has been investigated in several projects. Genetic typing of M. bovis isolated as a result of the Randomised Badger Culling Trial (RBCT) has shown that the same strains can be cultured from cattle and badgers in the same location. This suggests that transmission can exist between species but does not provide any information about which way the transmission went e.g. from cattle to badgers or badgers to cattle. Nor does this show the importance of any specific transmission route.
Spatial methods using databases incorporated into a global information system (GIS) have been used to look at the role of suspected environmental variables as risk factors for the disease in cattle, the results indicated a number of possible environmental correlates with disease incidence (SE3001). Other work in a similar vein using a non-GIS approach has confirmed some elements of the work in SE3001. The final report will be available soon.
Mapping the movements of cattle from the cattle tracing system database (CTS) with disease incidence around the country has shown us that cattle movements are an important route of transmitting bTB from one herd to another, particularly outside core hotspot areas (SE3034).
Post foot and mouth disease (FMD) in 2001 Defra commissioned a project to look at bTB risk to farms after restocking compared with those farms that did not restock. This work is ongoing and it is too early in the analyses to be able to give any results.
The spatial component of bTB in badgers has been investigated both in areas of the RBCT, and in the research station at Woodchester Park. The Woodchester Park data tells us that not all badgers in a social group may be infected with TB and though the infected individual may continue to live there for many seasons, the other members of the sett do not usually become infected.
An important area of epidemiology is in estimating the level of risk bTB poses to cattle from other wildlife. The prevalence of TB in British wildlife has been looked at recently in two projects (SE3009, SE3010), one conducted by the Central Science Laboratory and the other by Oxford University. Both have produced final reports and found that overall the level of risk of other mammals (excluding badgers) being a significant source of infection to cattle is extremely low. However, two species of deer were thought to present a higher level of risk due to their ecology and social interactions with cattle. The Department has taken these findings on board and has commissioned two projects to try to quantify the risk wild deer may pose to cattle.
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Page last modified:
July 7, 2008