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E pidemiological effects of badger culling and vaccination PowerPoint Presentation
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E pidemiological effects of badger culling and vaccination

E pidemiological effects of badger culling and vaccination

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E pidemiological effects of badger culling and vaccination

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  1. Epidemiological effects of badger culling and vaccination Rosie Woodroffe Zoological Society of London

  2. Two important facts about bovine TB TB is a huge problem for both beef and dairy farmers Badgers are part of the problem

  3. Epidemiological effects of badger vaccination and culling Introduction to disease dynamics Nonselective badger culling Badger vaccination Combined badger culling & vaccination

  4. Epidemiological effects of badger vaccination and culling Introduction to disease dynamics Nonselective badger culling Badger vaccination Combined badger culling & vaccination

  5. Susceptible and infectious hosts

  6. susceptible

  7. infectious susceptible

  8. Immunity

  9. immune

  10. Population structure is important

  11. 1981 0 1km

  12. 1981 1982 0 1km 1983 1984 1985

  13. Culling

  14. Fewer infected hosts Fewer susceptible hosts Less frequent contact between infected and susceptible hosts

  15. What nonselective badger culling is meant to do CULL • Reduce numbers of infected animals • Reduce onward transmission of infection to other badgers • Reduce onward transmission to cattle

  16. Badger densities were reduced inside RBCT culling areas; but their territorial and ranging behaviourwere also affected Triplet D proactive

  17. RBCT culling led to a rapid drop in badger numbers… but numbers of infected badgers fell more slowly As culls were repeated, the proportion of infected badgers increased prevalence (relative to first proactive) error bars show 95% CI

  18. What badger culling actually does CULL • Disrupts territorial system • Increases opportunities for contact between social groups • Increases opportunities for disease transmission • Increases number of cattle herds contacted by each badger

  19. Badger culling has two opposing consequences Fewer badgers - good Each remaining badger more infectious – bad

  20. How does changing badger density influence TB risk to cattle? reactive culling more cattle TB outside proactive West Somerset % reduction in badger density relative change in cattle TB incidence 20% 40% 60% 80% 100% West Gloucestershire less cattle TB proactive culling

  21. Vaccination

  22. Vaccination Removes susceptibles by making them immune No impact on those already infected Nevertheless, helped eradicate smallpox and rinderpest, and to control many other diseases e.g. measles, rabies, human TB

  23. What badger vaccination is meant to do vaccinate • No effect on already-infected animals • Reduce onward transmission of infection

  24. What vaccination is meant to do vaccinate • No effect on already-infected animals • Reduce onward transmission of infection

  25. What vaccination is meant to do vaccinate • No effect on already-infected animals • Reduce onward transmission of infection • Lowers prevalence over time as infected animals die off

  26. What vaccination is meant to do vaccinate • No effect on already-infected animals • Reduce onward transmission of infection • Lowers prevalence over time as infected animals die off • Population structure likely to enhance vaccine benefits

  27. Selective culling

  28. Vaccinate test-negative badgers Catch and test 60-80% of badgers no social perturbation Detect and cull 49% of infected badgers social perturbation

  29. CSL (now AHVLA) 2009: “if... [selective] culling produced no social perturbation then the reduction in the number of infected badgers, and the reduction in herd breakdowns, was greater than either culling or vaccination... If... culling resulted in repeated perturbation of social groups each time a badger social group... had an animal culled, then there was a dramatic increase in the number of infected badgers and the number of herd breakdowns” Bielbyet al (in prep) – effects of 1986-98 small-scale culls on badger populations in 1998-2002 Estimates of the threshold numbers of badgers culled needed to prompt increase in territory size

  30. Conclusions Nonselective culling, vaccination, and selective culling function by different mechanisms but in principal all have the potential to control wildlife disease Population structure can have a major impact on disease transmission rates Culling alters badger population structure in ways which accelerate transmission, undermining benefits for TB control By contrast, badger population structure is likely to enhance the efficacy of vaccination Badger vaccination is likely to be cheaper than culling, and is unlikely to cause harm; however its contribution to cattle TB control is not yet known