Saturday, April 30, 2005

The Tb Saga - A Vet's View.

Practising veterinarian, David Denny, B.Vet.Med, M.R.C.V.S from Worcestershire, has provided the editors with his overview of the bTb saga, past and present.

On testing:
"There was some satisfaction in testing cattle for Tb in the 1960's. Reactor cattle, some in advanced stages of the disease having been slaughtered, the remaining cattle passed their subsequent tests and farms remained free of Tb for 30 or 40 years. Job well done.

No longer: there is now despair and frustration. In spite of using a more sensitive test, finding reactor cattle is only the start of a major problem for all concerned.

In spite of the reactors being slaughtered, at subsequent 60 day or 6 month tests on virtually all farms, I find more reactors. The farms remain under restrictions - unable to move cattle on or off the premises (except for direct slaughter) The farm is unable to trade.

Usually cattle can leave their winter housing in the spring and go out to grass 'free of tb', only to react again in the autumn. (at a 6 month test). But it is not uncommon for cattle to become infected during the winter while housed.

In the 1960's, a double fence six feet apart was sufficient to stop the spread of bTb. now there is a lateral spread of two or three miles annually. Cattle in completely 'closed' herds (those who do not buy in cattle) are having Tb breakdowns. Cattle to cattle infection overall is minimal and insignificant. In several incidences, in spite of some reactor cattle with clinical signs of Tb ( coughing, nasal discharge, loss of weight etc.) that are confirmed as Tb postmortem, the remaining cattle from the same group have passed their two 60 day tests and the subsequent 6 month one. That hardly indicates a high incidence of cattle to cattle transmission."

"Doubts are now being made about the sensitivety of the intradermal test and the new blood test. That claim is based on the number of reactor cattle with 'Non visible lesions' at slaughter. The doubters show a complete lack of understanding of the disease process and the body response. Both tests look for response from the animal when it has met up (been challenged) with Tb. - an antigen, its immune status. Depending on the size of the challenge and its health status, the animal can either overcome the challenge and remain healthy, or the disease process progresses. In the case of Tb, which is a very slow disease to develop, it takes at least 6 weeks before any lesion in a lymph gland develops. More often than not, 'No Visible Lesions' is not a false positive as claimed, but an indication that the animal has been challenged with Tb, and is at an early stage of the disease process: if the challenge is small, then the animal will stop producing antibodies and pass subsequent tests.

The new blood test (Gamma interferon) is far more sensitive than the intradermal test, resulting in many more 'positives' and even more cattle being slaughtered. It is only of use when there is no reservoir of infection in the badgers (or avian - ed.)"

On badgers:
"Once badgers became a protected species in the 1970's, together with an increase of maize growing, there has been a population explosion: in some regions, a high proportion of badgers have Tb, coinciding with a high incidence of Tb in the cattle herds. Maize is a favourite food of badgers, who waive all 'territorial rights' for a feed. It is high in energy, offering badgers a higher survival rate. Unlike most other animals, badgers infected with Tb can take 3 or more years to die from it. For most of that time they are apparently healthy - capable of breeding etc., but they are infectious - able to transmit Tb to others. It is during their latter six months when they become 'ill', and suffer. Having been 'expelled' (from the group sets) they go into 'sheltered accomodation' in or close to farm buildings and an easy source of food. This is the most dangerous spread of Tb (for cattle). They spread Tb in their urine - 300,000 bacteria in a teaspoonful - which they dribble out as they move, and in their saliva - and so contaminate troughs and feed."

On Krebs:
" The Proactive culling, like Reactive has been sabotaged by the so-called badger protection groups, but this has not significantly reduced the badger population. Badgers are running around in broad daylight - so what must be happening at night? Since the traps have been placed on the runs and around the sets, it is only the healthy badger (although it may be infected) that is trapped. The terminally ill badger in 'sheltered accomodation', escapes. It is these badgers that are transmitting Tb to housed cattle. Since it takes these badgers six months to die, it will be at least a year before any improvement in the cattle situation can be expected. The termination of reactive culling was premature for that reason. Those responsible are ignorant of badger behaviour.

Another significant factor in the efficiency of the trial, is that within the culling areas there have been 10 - 20 % of farmers and other landowners who have forbidden culling on their properties. This has resulted in areas of very high badger population on them. Since badgers travel miles to feed, if infected, these badgers will act as reservoir of infection for cattle within the 'trial' areas. (editor's note: If a farm was under Tb restriction at the start of the 'trial', then it did not qualify to take part anyway, and no culling of any sort took place. A hotspot within a hotspot.)

"It is inevitable that given very close contact, an infected sow suckling her offspring, will infect them. Who could have designed a 'culling trial' which has a closed season of 3 months to allow this? The whole trial appears to revolve around the survival of the badger at the expense of the cattle. It (Krebs trial) is no more than an expensive charade."

On other players:
"I am under the impression that there is an orchestrated campaign to exonerate the badger from having any significant input into the transmission of Tb to cattle. A major part appears to be cleverly conducted by the Chief Executive of the NFBG Dr. Elaine King.

When reactor cattle are slaughtered in their thousands and while she appears happy for badgers to suffer from Tb, perhaps she can reveal what her motives are? The current scapegoats include the FMD debacle, inefficient tests both intradermal and the recent blood test, cattle to cattle transmission, badgers catching Tb from cattle, late testing, cattle movements and the involvement of deer. Anything to exonerate the badger from blame.

The ISG (Independent Scientific Group) of seven (5 being professors, only one a veterinary surgeon) which advises Ministers on Tb strategy, are either research scientists or statisticians (3). and have minimal field experience.

The conclusion:
Those of us on the front line, whether veterinary surgeons or farmers know that it is beyond all reasonable doubt that the badger is the reservoir of infection, and is by far the most significant factor in the Tb saga.

In that front line, there is frustration and very low morale. Any plans to implement further petty and irrelevant restrictions will result in a total loss of goodwill and a complete breakdown in co-operation. Until badgers are culled, the situation will only deteriorate. Why is acceptable to slaughter reactor cattle, many pedigree and heavily pregnant and not to cull the infected badgers who are responsible? Any reduction in Tb depends on co-operation of the farmers. If they are asked to take on more financial and other responsibilities they must be allowed to remove the reservoir of infection - the badgers.

Why should farmers have to 'stand and stare' (quote by a client after 15% of his pedigree cattle were found to be reactors) while their livlihoods and generations of work is destroyed as a result of Tb?

Professors do NOT have a monopoly of knowledge and statisticians in a remote office are NOT competent to determine future policy".

D.J.B. Denny 2005.

No comments: