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

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

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

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

Susceptible and infectious hosts

susceptible

infectious

Immunity

immune

Population structure is important

km

km

Culling

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

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

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

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

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 What badger culling actually does

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

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

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

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

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

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

vaccinate What vaccination is meant to do 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

Selective culling

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

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” Estimates of the threshold numbers of badgers culled needed to prompt increase in territory size Bielby et al (in prep) – effects of small-scale culls on badger populations in

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