Extra reading TB

Policy to control bTB is vigorously debated and contentious because of its implications for the livestock industry and because some policy options involve culling badgers, the most important wildlife reservoir

Includes- disease of cattle, affects humans and many other animals, since milk pasteurisation less of a problem in developed countries

problems of TB- advances cases loss of condition, developed countries: movement restrictions, mandatory slaughter, indirect losses to farmer 

 English and Welsh governments estimate that they have spent £0.5 billion in the last decade on testing, compensation and research with further costs being borne by the agricultural industry

 EU law currently prohibits the vaccination of cattle as it can mask the detection of infection

The vaccination of badgers is the subject of intense current research, and vaccination has been under way in Wales since 2012 

 The complex biology of the pathogen and its mode of transmission make the study of bTB epidemiology particularly challenging

 Efforts to control the disease regular testing of herds, destruction of individuals that test positive (37 068 cattle in 2012; a further 943 close contacts were also slaughtered) and post-mortem surveillance of all routinely slaughtered animals.

Where infection is detected in a herd, cattle sale and movements are restricted and contacts of the infected herd traced

 A recent rapid decline in bTB in cattle in New Zealand has, in part, been associated with control of a wildlife host species (the introduced brush-tailed possum) .The relevance of this programme to the British Isles is limited by the very different biology of the wildlife hosts involved and also because the rules governing cattle movement, disease compensation and other aspects of bTB policy are different in New Zealand 

Transmission occurs within cattle herds, and movement of undetected infected cattle can lead to transmission between herds . In ‘Officially Tuberculosis Free’ regions of Great Britain, such as Scotland, nearly all herd breakdowns can be convincingly attributed to cattle movement

Little is known about how M. bovis is transmitted between badgers and cattle

In designing bTB control programmes for known and potential high-incidence areas, benefits will be obtained from implementing effective measures that target the disease in both cattle and wildlife in the same area

Testing and surveillance 

There are several different methods available for diagnosing bTB infection in cattle, either alive or at slaughter. None of these is 100% sensitive, which means that infected animals are sometimes missed

The tests are also not 100% specific, which means that uninfected animals may sometimes be incorrectly identified as infected (false positives).

Sensitivity and specificity are usually defined with reference to a goldstandard test, which acts as the definitive arbiter of whether an individual is infected. There is no such gold-standard for bTB, and post-mortem investigations, which probably miss some infections, have to be used instead.

Testing and surveillance

The single intradermal comparative cervical tuberculin test is the approved stand-alone test for bTB infection in living cattle used in the UK and the Republic of Ireland. It has high specificity in individual animals, and a recent meta-analysis of current diagnostic tests found a median value for the animal level specificity of the SICCT test to be above 99%. The same meta-analysis estimated the mean herd-level sensitivity to be 49%

In 2012, slaughterhouse testing accounted for nearly one-quarter of all new confirmed breakdowns in cattle herds across Great Britain

Biosecurity

 Cattle movements, especially movements from high incidence areas, are associated with increased risk of the onward transmission of bTB...pre movement tests...Scotland: post movement tests, provide incentive to buy from low disease areas.....double fencing prevent cattle contact...feed off floor, limit badger access, section off setts and latrines

Culling badgers can affect the incidence of confirmed bTB in cattle herds in Great Britain

 Culling badgers is known to disrupt badger social structure, and this has been shown to cause badgers to move more frequently and over longer distances

It is not currently known whether alternative culling methods (e.g. shooting of free-ranging badgers or snaring) could reduce badger densities more or less effectively in Great Britain than the cage trapping

Vaccination 

To vaccinate cattle against bTB, a BCG vaccine (a live attenuated strain of M. bovis that is widely used in humans) exists, but it is not yet licensed for use in cattle and such use is currently prohibited by EU regulations.... BCG vaccination of cattle leads to false positive reactions

As with cattle, the main protective effect for vaccinated badgers is to reduce the severity and progression of disease upon challenge with M. bovis