Committee Reports > List of Committees > Dáil > 1986 > Committee on Public Expenditure > Report - Review of Public Expenditure for the Eradication of Bovine Tuberculosis

APPENDIX V

OF

THE IRISH VETERINARY ASSOCIATION

ON

THE BOVINE TUBERCULOSIS ERADICATION SCHEME, 1955 - TO-DATE*

The objective of the scheme is to eliminate M. bovis in cattle to the extent that cattle will not be a source of infection.

BACKGROUND

Nowadays infection with M. bovis rarely gives rise to clinical disease in cattle. Infected cattle are most commonly identified:-

(a)at meat inspection (0.26 per cent of attested cattle have lesions at slaughter).

(b)in tuberculin tests viz. (i) round tests (0.23per cent of attested cattle show positive reactions); (ii) reactor retests; (iii) special check tests, i.e., tests on herds out of which lesion-positive cattle have been slaughtered, tests on herds contiguous to infected holdings, and tests conducted on randomly selected herds in areas of high prevalence, and (iv) pre-movement tests, and

(c)on clinical and/or epidemiological grounds.

Impediments to eradication to-date are related to

(a)The organism: M. bovis survives well outside the animal body. Only a small number of viable organisms are required to set up infection. Infected cattle are likely to remain infected for life and established cases commonly are a source of infection for other animals and their environment. Other animal species (e.g., man, deer, goats, badgers) also become infected and may serve as reservoirs of infection for cattle.

(b)Inherent limitations of the tuberculin test : The standard single intra-dermal comparative tuberculin test (S.I.C.T.T.) generally has a sensitivity in the 75-85 per cent range; this may be lower in cows. There is therefore a distinct possibility that a proportion of infected cattle individually may not react positively to the standard S.I.C.T.T.

The sensitivity of the test is improved when the so-called “severe interpretation” is applied. However this in turn reduces the specificity of the test and, if generally applied to the cattle population, a number of non-infected cattle would be likely to be removed as “reactors”.

The test is a comparative one and requires the simultaneous inoculation of two tuberculin antigens: one of these is an avian tuberculin to which cattle in up to 35 per cent of herds react positively. In such cattle the reaction to this antigen is normally taken into account when interpreting the significance of the animal’s reaction to the bovine tuberculin.However, the extent to which reactivity to avian tuberculin masks reactivity to bovine tuberculin attributable to M. bovis infection is not clear: it may be significant.

* Eradication has been compulsory in the twenty-six counties only since June 1962.

The E.E.C. Directive No. 64/432, as amended, is the basis for the use of the tuberculin test within the community. This states that “a reactor is an animal which, by reason of a test or otherwise, a Veterinary Inspector believes or suspects is affected with bovine tuberculosis or is capable of infecting other animals with bovine tuberculosis”. Also, the E.E.C. Directive, at Annex (B), requires that animals which are positive to the comparative test must be removed as reactors. It is important that the veterinary surgeon carrying out the tuberculin test recommends, on the test report, the removal, as reactors, of animals which he suspects may be infected, irrespective of the lack of a significant increase in skin fold thickness on test. Even when clinical signs are absent, he/she may recommend, on epidemiological grounds, the removal as reactors, of those animals which show inconclusive or negative responses to the comparative test (T.B. 25, Rev. 1981, Department of Agriculture).

The tuberculin antigens currently in use are considered to be the best available. However, the “tuberculin test” relies solely on post-mortem findings for confirmation of its effectiveness: the efficiency of the tuberculin test - a field test - is not the subject of corroborative investigation under controlled laboratory conditions.

Both the tuberculins currently in use, and the test interpretation procedure employed, differ considerably from those used at various times during the 1950s, 1960s, 1970s and the early 1980s, and are, in effect, relatively more reliable than those used earlier in the scheme. Based on current evidence it is likely that the overall prevalence of tuberculosis in cattle in the earlier years of the scheme was significantly under-estimated and/or reported.

Accordingly, comparisons between the current situation and the earlier phases of the scheme are grossly misleading.

(c)The persistance of infection in infected holdings : The identification of an infected animal as a “reactor” has tended to be regarded almost as an end in itself rather than as only the initial step in eradicating the infection from that holding and from that locality. The control and sanitation of the infected holding, once identified, and the control of the cattle on such premises, are central to eradication. The actual cost of these measures, and of identifying and eliminating the original source of infection in each outbreak, is considerable, and tends to be underestimated.

(d)The definition of a “holding” : The operation of “fragmented holdings” as single units within which cattle may be moved without testing or other restrictions, is unsound and seriously threatens the success of the scheme. Likewise, the freedom of herd owners to walk their cattle on roads together with the poor quality of fencing between neighbouring farms, compromise the definition of “a holding”, and undermine effective control procedures.

(e)Movement of known infected cattle : Once infected cattle have been identified, by the test or other means, the responsibility for their disposal is left to the herd owner who may encounter considerable difficulties in arranging the animal’s slaughter in terms of both their transport and their acceptance for slaughter at a satisfactory price. Failure to provide a collecting service for tuberculous cattle, so as to ensure their early and direct delivery preferably to a designated meat plant, is a further impediment to eradication because it fails to emphasise the importance of early removal of such animals to the control and eradication of tuberculosis from the holding. In certain instances also it has led to illegal traffic in known infected cattle.

(f)Under-utilisation of veterinary meat inspection as a means of monitoring attested slaughter cattle for evidence of tuberculosis : Under the conditions prevailing in most export meat plants, the likelihood is that for every carcase found to have tuberculous lesions, another infected carcase is missed. This applies to both attested and tuberculin-reactor cattle.

Improvements in inspection efficiency would necessitate reductions in line speeds, improved inspection facilities, the provision of additional inspectorate staff, revised inspection procedures, and the provision of more extensive laboratory support, both locally and centrally*. Such measures, if implemented, would be of considerable benefit to the scheme.

At present, post-mortem examination of carcases at non-export plants, in the most part, is only nominal at best.

The control of tubercle-infected material, including effluent at meat plants, is less than complete.

(g)Patterns in livestock trade : Movement of cattle within the State is a highly significant factor contributing to the spread of M. bovis. The use of the pre-movement test is of some benefit, but this procedure does not apply to all cattle, since animals involved in hon-E.E.C. trade, and calves under six weeks of age are exempt.

In addition, there are no effective means available for controlling farm to farm sales/movements, and it is likely that a proportion of cattle move from farm to farm without test, since no movement permit system is in operation, nor do all herd-owners keep stock-books, as is required in other countries.

The ability of the Government to apply epidemiologically-sound restrictions on animal movement within geographically defined areas in which infection is particularly prevalent, apparently is limited, due to the constraints such measures would impose on “technically-free” herds in such areas, despite the fact that infection may be rampant in such areas.

* There is one laboratory, located in the Veterinary Research Laboratory in Dublin available to support the eradication scheme nationally.

(h) Government Attitudes : The scheme is regarded as a “loss maker” rather than as a “market saver”. But without the scheme, the marketability of Irish meat and dairy products would have been seriously jeopardised during the past three decades. To that extent, the scheme to date has been a qualified success.

Any scheme in operation for thirty years would have benefited from critical management and performance appraisal on a regular basis. The various official publications issued on the progress of the scheme during this period have been incomplete, and on specific points, misleading. Failure to take into account the effects of biological factors - as outlined at (a) and (b) above - on the efficiency of eradication measures, and failure (a) to institute proper performance assessment procedures on a programmed basis, and (b) to adopt novel measures as dictated by local requirements (e.g., the purchase of entire herds rather than individual reactor animals, and the application of the standard E.E.C. tuberculin test interpretation procedure in specific cases), have delayed the progress of the scheme.

The enforcement of the Diseases of Animals Act of 1966, in regard to prosecutíons has not been as actively pursued as it should have been, with due deference to the judicial procedure.

CONCLUSION

The 1985 programme takes cognisance of many of these points but in some respects is seriously compromised by consideration of farmer interests. Unless the finding of tuberculin reactors comes to be regarded as an indictment of that herd owner’s ability adequately to maintain the security of his/her holding, and to buy wisely, unless such a catastrophe comes to be regarded as an occasion for local community action, and unless the Government introduces improved measures (a) for identifying infected cattle and (b) for restricting movement of the cattle out of known infected areas, tuberculosis in cattle will be a serious impediment to trade, on the grounds of animal and human health, possibly for the next decade.

October 1985