Human TB – Bovine TB. Lessons to be learnt and three simple questions for DEFRA

While Defra hold on to a now disproven view that badger culling is needed for control of bTB in cattle, there remain important omissions, contradictions & unanswered questions in their approach to the current management policy.

For a start, the management of Bovine TB (bTB) is still plagued by the inaccuracies of currently used tests and testing systems. Importantly, none of the primary tests currently used can identify the presence of live Mycobacteria which is core to the central dogma of bacterial diagnosis developed by Robert Koch, one of the main founders of modern bacteriology.  He discovered the causative organisms of anthrax (1877), septicæmia, tuberculosis (1882) and cholera (1884). Koch’s dogma or principle, specifies that definitive diagnosis is dependent on the identification of the presence of the infectious organism.

There are major concerns about elements of the front-line bTB tuberculin skin-test. Firstly, it misses a substantial proportion of infected animals, thus allowing undetected infection to circulate in and between herds. Secondly, repeated injection with the tuberculin injection used for the skin test may potentially render an animal skin-test positive, despite there never having been any infection. Thirdly, the implementation of the skin-test is laborious and time-consuming, and requires multiple visits to the farm by a vet, hence while it creates work for vets, it is expensive.

In Human TB (hTB) the basic biology is similar. Recently, however,  the human TB clinical fraternity have become increasingly concerned about the TB skin-test. In fact the concern has been such that the Centres for Disease Control (CDC), based in the US, now recommends the use of the TB blood tests (IGRAs), such as QFT-Plus (similar to Bovigam) over the TB skin test (TST) for most risk groups.

To illustrate the importance of this change of approach, clinical studies on the phage-based test ‘Actiphage’ have shown for the first time that live bacteria can be detected in the blood of people with incipient TB infection, including contacts of infected patients. This success was mirrored by the data produced by vet Dick Sibley at Gatcombe who used Actiphage and Bovigam (gamma interferon) to effectively eradicate bTB from the farm on two occasions. Those studies showed clearly that the best way to identify infected animals was the combined use of Bovigam and Actiphage, and not skin-testing. They indicated very strongly that the biggest problem in the eradication of bTB is the inability of skin-testing to identify infected carriers which actually maintain the infectious burden within the herd. They also imply that there is no significant involvement of external non-bovine hosts in the propagation of the disease.

So, the questions we would like to put to  George Eustice and DEFRA are:

1) Why have you not implemented a controlled trial on the efficacy of different testing strategies for Bovine TB?

2) Why will you not take note of the human TB data? This  clearly shows that identification of the live bacteria is the critical key to controlling this disease.

3) When will you recognise that all the data from both bovine and human TB indicates that there is no justifiable scientific rationale for the involvement of an external host to maintain persistent infection in the herd?

 

DEFRA called out over flawed bovine TB claims at international vet conference

The UK’s Animal and Plant Agency statistician Colin Birch was roundly criticized for his presentation yesterday (12/08/22) at the 16th International Symposium of Veterinary Epidemiology and Economics (ISVEE 16) held at Halifax Convention Centre, Halifax Nova Scotia, Canada.

Birch presented data from badger killing zones in England in recent years, with no proper explanation as to why he had not also used data from unculled areas to compare. He claimed  that a reported 50% reduction in bovine TB herd incidence in culled areas was due to badger culling.

The audience seemed less than convinced. At the end one question pointed out that it is not possible to attribute the reduction in bTB incidence to badger culling as the reduction in the unculled area had a similar trajectory. Cattle measures (Testing and movement controls) that were introduced prior to and over the same period (in both culled and unculled areas) would reduce incidence in the manner observed.

A further point was made from the audience that it looked like Birch and APHA were trying to make and promote ‘policy driven evidence’ to satisfy the ministry (Defra). Birch had no coherent response to this but said that he did not agree.

The unpublished manuscript by Birch and others is yet to be fully disclosed, but comes at a highly sensitive time for Defra and Minister George Eustice and Natural England Chairman, Tony Juniper and his scientific staff. They want to sign off the killing of another 40,000 largely healthy badgers from September of this year, despite the science suggesting that complete failure is the most likely outcome.

In March of this year, Defra issued flawed data (see here) in response to a detailed peer reviewed paper (see here) published in Veterinary Record which showed that badger culling in England since 2013 has failed. In a response to the paper, Defra produced a media outburst designed to undermine it, that claimed badger culling had little or no effect in the first two years, and therefore the analysis used was flawed. Observers have been left baffled and talking about government competence, since all the Defra data presented shows large drops in herd incidence over the first two years, suggesting that it is cattle measures that are responsible for these declines, and not culling.

Despite high public interest in this most controversial of policies, Defra have become tight-lipped on their home-made dilemma since March 2022, and defiantly issued more cull licences in June. But despite well and truly losing the science argument they still  appear desperate to try to show some reason to prop up their policy and to enable them to keep killing badgers. This fell flat at today’s conference as the science community strongly questioned Defra’s handling of data.