G Nugent & B Warburton Landcare Research, P.O. Box 40, Lincoln, N.Z

1. Can TB be eliminated from possums in large forest areas?Local elimination - Proof of concept of eradication G Nugent & B Warburton Landcare Research, P.O. Box 40, Lincoln, N.Z Tb bacillus

2. Outline • TB history • Proposed future for TB-possum management • Local Elimination • Proof of concept of eradication trial TB lesion in cow head TB lesion in possum armpit

3. Trends in TB in livestock • 30 April 2010: 95 herds infected, probably <50 caused by possums • >94% reduction in livestock TB in 15 years • => Now no doubt that possum control is being successful in most areas

4. NPMS review and new proposal • Current National Pest Management Strategy for bovine TB aims to reduce TB in livestock to <0.2% by 2013 • It does NOTaim to eradicate TB from possums • TB has been eliminated from some small areas • BUT no proof yet TB can be eradicated from possums in large tracts of native forest in which TB is long established

5. Can TB be eradicated from a wildlife host? • One country (Oz) has eliminated TB from wildlife host • But from Buffalo • Big and easy to see, and muster or shoot • Much harder from possums?

6. NPMS TB: New proposal (2009) • Extend strategy to 2025 New objectives: • To reduce area with infected wildlife • To obtain proof of concept that TB can be eradicated from the wild across large forested habitats • NB: Also, clarify legal responsibilities for reporting animal ID information from slaughter TB vector free

7. 1.0 0.8 0.6 0.4 0.2 0.0 Eradication requirements: 5% RTCI 2% RTCI • Intensive possum control to break cycle in possums • Model: >99% prob of Tb extinction in 5 y at <2% RTCI • Maintain low possum numbers till SPILLBACK risk is zero • Infected female deer can remain alive and infected for 10-15 years 1% RTCI Probability of Tb extinction Predictions of a spatial possum-Tb model 0 1 2 3 4 5 6 7 8 9 10 Years SPILLBACK RISK: Possum eating pig mesenteric tissue

8. Three phases in TB eradication • Initial knockdown • Reducing possums from carrying capacity to below ~0.4 possums/ha. • Maintenance • Possum densities kept at this low level 10-15 y to allow bTB to die out • Proof of Freedom (POF) • surveillance data used to assess objectively the likelihood that bTB has been eradicated successfully

9. ExampleBlythe Valley; 13,000 ha hilly farmland, N Canterbury Possum control started 2000 No possum control 30% 20% Possum control RTCI 10% 0% 1991 1994 1997 2000 2003 2006 2009 Rapid initial knockdown (by ground-based methods)

10. Maintenance control • 4 yrs trapping • Index-removal-index estimator • Only 30 possums now present • 0.002/ha • Too low to sustain TB?

11. ‘Proving’ freedom: Step 1 Have we done enough? Predicted effect on possum Tb 1.0 • Model predicts 99% prob Tb eradicated from possums by 2005 IFthe high intensity of control had been applied evenly 0.8 0.6 extinction Probability of Tb 0.4 0.2 0.0 2000 2002 2004 2006 2008 Year

12. Proving TB Freedom Step 2: Validate model predictions with surveillance data • Multiple data sources: • Livestock Tb testing • Wildlife necropsy • Possum trapping Bayesian Framework

13. Prob TB absence in possums Blythe Valley 2006 predicted probability = 10%* • If possums almost eliminated a single survey can provide >99% confidence Tb is absent * Conservatively set high

14. Local elimination of possumsControl at zero density Three components • Maximise initial knockdown: >99% reduction • Already achievable - 0% RTCI already common • Focus now on cost reduction • Mop up: Detect and eliminate any survivors • Requires cheap detection method • Preventing all or most reinvasion: • Difficult but not issue if surrounding area controlled

15. Initial knockdown: Hauhungaroa 2005 Example • 88,000 ha treated with aerial 1080 • 2 pre-feeds, cost $60/ha • Monitored by 512 traplines • RTCI = 0.045% (50 x lower than 2% target) • Predicted prob Tb extinction > 99% in <5 yr • But repeat control still needed - because of deer spillback risk

16. Mop-up of survivors key step • Development of Chew Card as low-cost but sensitive detection devices • To mapwhere survivors are still present • So they can be targeted by follow-up or mop-up control

17. Possum Detection Probability DNA extracted from Chewcards and trapped possums >80% of possums detected by Chewcards (when spaced 50m along lines 250m apart) BUT only 40% of the possums present trapped => not ideal, but adequate if control annual

18. Local eliminationCurrent status • Conventional aerial ops can deliver knockdown to near zero density • Feasible to prevent population recovery through annual detect-and-mop-up control • If not reduce further • Difficult to prevent re-invasion • But with regional-scale control to low density not an issue

19. Proof of concept of eradicationproposed trials • Two areas ID’d as possibilities: • Hokonui, Southland • Rangitoto/Hauhungaroa (RHR) • RHR: Established focus of TB • >50% adult female deer infected, most pigs historically. • Some controlled since 1994, others not till 2005. • TB-infected deer killed in 2008 • Farms periphery still infected 2009 TB lesion, red deer lungs

20. Otago Daily Times 21/01/2008 ‘Standard’ eradication recipe for ‘deep’ forest • Conventional broadcast aerial 1080 with 1-2 prefeeds • Reliable intensive control • Repeat 3 time at ~5 y intervals • To keep possums v low for >15 yr • RTCI monitoring • To confirm UNIFORM low possum density • Pig and deer Tb survey AHB Design best practice (Draft)

21. Alternative 2: Low-cost aerial • 2nd & 3rd aerials at half cost • If first control highly effective • Use low-sow techniques • Potentially = broadcast? • But even if not adequate to prevent spill back?

22. Option 3: Targeted aerial • Reduce cost of 2nd & 3rd aerial by targeted low sow • Use detection surveys (Chew Cards) to identify areas with most possums • Same cost as option 2, but less 1080. • Plus extra surveillance data from simultaneous possum/pig/deer survey 2006 Chew Card survey: Large areas with no possum detections

23. Option 4: Detection and Ground-based Mop-up’ • Use detection surveys (Chew Cards) to identify areas with possums • Annual or biennial. • Plus extra surveillance data from simultaneous possum/pig/deer survey • Only need aerial1080 for first knock down

24. Eradication proof of concept trial • 2011-2025: • Compare speed & cost effectiveness of 4 diff approaches • Standard – conventional broadcast aerial, RTCI monitoring, pig and deer Tb survey • Low sow (half price) standard aerial RTCI monitoring, pig and deer Tb survey • Targeted low sow: Low intensity detection CTCI surveys to systematically map possum distribution, and target option 2 at <50% of area • Ground-based detection & mop up incorporating possum, deer and pig surveillance annually.

25. Eradication proof of concept Illustrative scenario ($/ha)

26. Summary I We can: • Reduce possums to near zero • Detect survivors with high sensitivity • Mop up survivors at > reproductive rate => Local elimination feasible

27. Summary II At the same time we can also : • Show many sites have no possums (= no TB) • Proving TB can be eradicated may be easy? • And it may be achievable more cheaply and quickly than current practice