Does Badger Culling have a part to play in the Control of Bovine TB?

Transcription

1 Does Badger Culling have a part to play in the Control of Bovine TB? Roger Blowey BSc, BVSc, FRCVS, FRAgS Wood Veterinary Group, 125 Bristol Road, Gloucester, GL2 4NB rogerblowey@mailbox.co.uk

2 Overview Standard approach to disease control Evidence relating to removal of infected badgers What do other countries do? Could we improve our current approach What are the other options? Was the Gloucestershire cull effective? Social and human cost

3 State Disease eradication policies Brucellosis identify infected animals + cull; vaccination to prevent spread, then final test + cull to eliminate Warble fly remove reservoir (imports) then enforced treatment at susceptible stage Anthrax remove reservoir (M+BM) by test + destroy infected carcase. Prohibition of M+B meal BSE identify source of infection (M+B) and remove

4 State Disease eradication policies EBL + FMD EBL identify reservoir (imported cattle) + remove FMD 1967, 1981, 2001, Identify source, reduce spread, remove infected animals

5 State Disease eradication policies -TB Test + cull infected cattle Identify + remove the reservoir Worked well from 1930 s to 1970 s, with around 400 reactors pa in 1970 s + 80 s

6 Testing cattle worked well in 1950 s + 60 s

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8 The massive surge in btbhas occurred despite increasing cattle controls Premovement testing Testing of all adult stock, no longer able to omit beef cattle Whole herd movement restriction if IR (= inconclusive reactor) identified Second time IR animals are culled Auditing of vets doing TB testing (+ prosecutions where its shown to be incorrect) Far fewer farms and batches of animal movements than 30 years ago

9 History of TB Control 1920 s TB a problem in cattle and man 1930 s pasteurisation of milk 1940 s??? 1950 s voluntary TB accreditation. Double fencing 1960 s compulsory eradication 1970 s down to 400 reactors per year, but fell no further, ie numbers started to plateau TB found in badgers in Glos 1973 badger protection to prevent badger baiting 1981 protection of badger setts

10 History of TB Control Thornburyarea cleared of badgers and TB disappeared for 10 years 1980 Dunnetreport. Welfare doubts on cyanide gassing Para 56 : unnecessary and indeed a waste of resources to seek further confirmation proactive culling banned. Clean ring trapping 1997 Krebs report. Questioned the validity of Thornbury trial no controls Total ban on badger culling John Bourne starts randomised badger culling trial 2007-Chief scientist s group contradicted ISG s conclusion

11 History of TB Control 2008 Jenkins and others show that in the 2 years following the end of the RBCT, in proactive areas TB decreased by 60%, and that there was no longer any evidence of the perturbation effect We know that skin test does work clearance of TB from herds in Northumberland post FMD restock Used widely in other countries to achieve effective TB control, provided wildlife reservoir is reduced

12 PERTURBATION -Estimated effects of proactive culling on the incidence of confirmed cattle TB breakdowns inside trial areas and up to 2 km outside trial area boundaries (DEFRA)

13 What happens when you remove the reservoir?

14 The Evidence so far Area (sq km) culling herd outbreaks Thornbury % Clear for 10 years Steeple Leaze % Clear for 7 years Hartland Point 64 >80% 80-90% reduction 10y East Offaly 738 >80% 88% reduction 7y Four Counties 100 x 4 >80% 60-80% reduction RBCTs 100 x % 19-23% reduction inside 22-29% increase outside

15 Thornbury removal of badgers gave no TB for 10 years, but an increase as soon as badgers returned The Thornbury Trial CATTLE HERDS WITH CONFIRMED TB AND BADGER SETT NUMBERS Number of herds Number of setts Years 0 control started control ended

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17 How have other countries eliminated Australia culled infected wild buffalo NZ cull infected possum Ireland cull infected badgers France cull infected badgers the problem?

18 Remove only infected setts? WoodchesterPark shows that some setts remain clean even when surrounding setts are infected Likely to be more acceptable to Society at large if only infected setts were removed Make use of badger nocturnal habits

19 Are TB reactor cattle infectious? They can be! Milk from infected cows CAN spread TB to calves After housing two naturally occurring reactors with 10 clean cattle for 12 months fourbecame infected, showing that prolonged close confinement can result in transmission (Costello et al, 1998). Not the major source however Analysis of new outbreaks by the epidemiology Unit at Weybridge, found that 90% of new herd incidents were considered to be of badger origin

20 But lots of evidence for low rate of spread 200 rector cattle from the trial areas were tested for infectiousness by culture of samples of nasal mucous. All were negative (ISG Report, 2007,appendix 1,p 234). In another project 41 reactors were serially sampled but all 1080 samples of nasal mucous cultured were negative for M.bovis (Vordermeier, 2007) no transmission between 22 naturally infected reactor cattle and 32 uninfected contacts, whilst open housed or kept in paddocks together for from 4 to 9 months (O Reilly and Costello,1988). Yet 20/22 showed gross lymph node lesions and serial section of lungs found mostly small gross lesions in 12 with eroding bronchial lesions apparent in 9 pairs of lungs.

21 Is Vaccination an option? (Chambers et al) BCG a poor vaccine in man s/c badger vaccine reducestb excretion from experimental challenge, but all badgers became infected. Does not work if badgers are already infected i/m vaccine easier, but even 10x vaccine dose was only able to reduce the number of infected tissues at and reduce the level of excretion

22 And of we don t remove the 2013 cull -4 badgers shot from heavily guarded sett (WBP) One (pic) with bad abscesses (+ smell!), other 3 all positive for TB Small pedigree Charolaisbeef unit may have to slaughter all its stock. Adjdairy farm lost 15 cows Do we really want our children walking over TB infected ground? Do we really want our badgers dyingwith this horrible disease? infection.

23 Did the Gloucestershire cull achieve its targets? Safe, humane and effective Need to await final report on PM s etc Safe no injuries reported Humane wounded badger did not report any injuries Effective 921 removed = only 40% of AHVLA estimate. No badgers seen by the 30 contractors for the final 3 4 nights, so probably less than 30% remaining. Gloscondecided to end the cull Social and human cost

24 Social and human costs Defamatory postings on Facebook etc Continual phone calls through the night; Rape alarms Obstructing farm drives; tracker devices on cars Trespass, balaclavas; torches in faces, through windows Intimidation of children and elderly Passing details to telesales, leading to frequent cold calling. Confusing for the elderly. Damage to property = traps

25 The Future? Somehow we need to get reasoned opinion on side I don t understand why its acceptable to cull rabbits, rats, mice, wild boar, deer, elephants etc, but not badgers Vaccination may have a part to play to prevent spread of TB in edge areas, but will not be effective in the face of heavy challenge