Friday, February 06, 2004

Parliamentary Questions

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Mr. Paterson: To ask the Secretary of State for Environment, Food and Rural Affairs what the sensitivity of the test used on translocated badgers is in (a)positive response and (b)negative response. [150583]

Mr. Bradshaw: The test, which is generally used, for the detection of TB in translocated badgers is a test for antibodies (the Brock Test). This is generally accepted to have a low sensitivity (the ability to detect diseased animals). However it is difficult to give accurate values for the sensitivity because euthanased animals are not always subject to laboratory culture.

Where a badger translocation is carried out under licence (from Defra or English Nature) each individual badger is tested three times. If any of the three results are positive, the badger is euthanased. Any other badger that has been in contact with the positive testing badger is also euthanased, regardless of the results of its own tests

Where an orphaned or previously injured badger is translocated by an animal centre or similar body they follow a voluntary code of practice (drawn up by the RSPCA, National Federation of Badgers Groups and Secret World Wildlife Rescue). Any animal to be relocated is tested three times and, if it tests positive, is euthanased. This protocol does not advise in the destruction of badgers who have had contact with a test positive badger. It should be emphasised that this voluntary protocol was not devised or approved by Defra.

The Veterinary Laboratories Agency is trying to develop a range of TB tests for badgers with improved accuracy, including a gamma-interferon test.

Mr. Paterson: To ask the Secretary of State for Environment, Food and Rural Affairs how many herds were placed under TB restriction in December 2002; and how many of those same herds were still under restriction in October 2003. [150571]

Mr. Bradshaw: A total of 725 herds were placed under movement restriction in December 2002. This includes 294 herds placed under movement restriction following disclosure of a new TB incident. The remainder were herds placed under movement restriction because the routine herd test was overdue.

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Ninety six herds placed under restriction in December 2002 were still under restriction on 31October 2003 (66 of those as a result of an ongoing TB incident).

Mr. Paterson: To ask the Secretary of State for Environment, Food and Rural Affairs how many herds require 60-day testing for tuberculosis; and what the estimated annual cost is for this testing programme in 2003–04. [150587]

Mr. Bradshaw: All herds suffering a TB breakdown are subject to at least one short interval ("60-day") test. A total of 7,275 short-interval tests were carried out from April to December 2003, at an estimated cost (including administration costs) of £3,485k. The forecast cost for 2003–04 is £4,600k.

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Mr. Paterson: To ask the Secretary of State for Environment, Food and Rural Affairs

(1) pursuant to her answer of 8December 2003, Official Report, column 215W, what epidemiological inferences can be drawn from the observed seasonal trends in the incidence of TB in cattle; [150596]

(2) what further research she is planning into seasonal trends in the incidence of TB in cattle. [150712]

Mr. Bradshaw: The absolute number of new TB incidents disclosed every month is closely correlated to the rate of testing. Hence, the majority of incidents are detected in the winter months (October through March), when most herds are tested.

However, if the data are adjusted to take into account the seasonality of TB testing, there does not appear to be a clear seasonal pattern in the rate of new TB incidents disclosed each month (i.e. it is not possible to conclude that the herd incidence of bovine TB in certain months of the year is consistently higher than in other months).

Because of the difficulty in studying seasonality of TB infection, there are few reports investigating this aspect of the disease. However, the results of one such investigation was reported in a paper by Wilesmith et al (1982)1. They examined seasonal variations in the risk of acquiring infection between 1971 and 1976 for a Dorset cattle herd during an extensive TB herd breakdown. The data indicated that the April/May period presented the time of greatest risk. This correlated with possible exposure to re-infection at the start of the grazing season, exposure lasting for a relatively short time. However, re-exposure to infection was not necessarily the same as re-exposure to pasture, since some stock were out-wintered.

The Veterinary Laboratories Agency will continue to monitor epidemiological trends, including seasonality.

1 Wilesmith, J. W, T. W. A. Little, H. V. Thompson and C. Swan. (1982). Bovine tuberculosis in domestic and wild mammals in an area of Dorset. I. Tuberculosis in cattle. Journal of Hygiene, Cambridge 89: 195–210.

Mr. Paterson: To ask the Secretary of State for Environment, Food and Rural Affairs what percentage of M. bovis was isolated from (a)carcasses and (b)faeces from wildlife species tested in studies carried out by or on behalf of her Department and its predecessor since 1974. [150611]

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Mr. Bradshaw: The information is as follows:

(a)All previous Defra information on M. bovis isolated from wildlife carcases was collated in the following review paper: Delahay, R. J., de Leeuw, A. N. S., Barlow, A. M., Clifton-Hadley, R. S. and Cheeseman, C. L. (2002). "The Status of Mycobacterium bovis Infection in British Wild Mammals: A Review". Veterinary Journal 163, 1–16.

(b)Two projects currently in progress involve sampling both live animals and carcase material from a variety of species. The data from these projects have not been fully analysed at this point so accurate figures are not available. Results from carcase material published in the OIE report on Wildlife disease 2003 showed that the prevalence of M. bovis infection was 2.9 per cent. in wildlife (669 cadavers, 20 positive cultures). The culture positive species were fallow deer, fox and muntjac.

Live sampling (samples including faeces) from over 4,000 small mammals (<30g) have shown that the prevalence of M. bovis is less than 0.3 per cent. The spoligotypes associated with these animals are largely of a type only found in small mammals.

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Mr. Paterson: To ask the Secretary of State for Environment, Food and Rural Affairs pursuant to the answer of 8 December 2003, Official Report, columns 21–18W, under what circumstances genetic structures of M. bovis undergo mutation following sequences of transmission, with particular reference to transmission between species; at what rate mutations occur; whether techniques and facilities are available to detect these changes; and whether back-mutation of bacilli from final host species would assist in the determination of the direction of inter-species transmission. [150847]

Mr. Bradshaw: As Mycobacterium bovis is transmitted over time there is evidence that hyper variable regions of its genome change, although most of the genome remains stable. Changes can be identified using molecular biological techniques. Hyper variable regions may change in both intra and interspecies transmission. There is no reason to believe that, except for very rare adaptive changes, the rate of mutation will increase as a strain moves between species.

The rate at which mutations occur depends on the region of the genome. Hence, single nucleotides have an average rate of change of about 10- 9 per nucleotide per generation. However, tandem repeats that show variable numbers (variable numbers of tandem repeats, or VNTRs), show a greater rate of change. Spoligotype changes are intermediate in rate between VNTR and single nucleotide mutations.

We use two main techniques to detect genetic variation in M. bovis. The first of these, spoligotyping, exploits a polymorphic region direct repeat (DR) locus in the genome that is composed of multiple 36bp DR copies interspersed by unique spacers, with strains varying in the presence or absence of spacers. The VNTR method targets 6 alleles (A-F) that vary in the length of internal repeat units, permitting strains to be differentiated on the number of repeats at each target; i.e. 7–5-5–4-3–3-3 would have 7 copies of allele A, 5 of B, etc. High throughput facilities for both of these techniques exist at the Veterinary Laboratories Agency

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(VLA), allowing the molecular typing of about 4,000 to 5,000 strains per year. Our current models of the population structure of M. bovis suggest that the VNTR loci evolve faster than the DR repeat locus. Thus spoligotyping provides a global picture of the population structure and epidemiology of M. bovis in Great Britain, while VNTR typing has proved useful as a fine scale method for detecting local changes in the M. bovis population.

The evolution of the members of the Mycobacterium tuberculosis complex has led to specific host preferences; hence M. tuberculosis appears human restricted, while M. bovis consists of a series of clones with a wider mammalian host range. The process of host adaptation probably involves a number of discreet mutations, which would all need to revert to reverse the host adaptation. Back-mutation i.e. the reversion of mutations, occurs very infrequently. The rate for a specific single nucleotide reversion would be about 10- 9 X 10- 9 ( or 10- 1 8 ) per nucleotide per generation. Indeed, if some of these mutation events were deletions they could not revert without the re introduction of the DNA. These questions are being investigated using laboratory based molecular biological techniques at the VLA.

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