216 B.M. Buddle et al.
Assuming widespread annual deployment,
the beneficial effects of badger vaccination
should accrue over time as the proportion of the
population vaccinated increases and animals
with pre-existing infection die off naturally.
There is currently no empirical evidence on the
optimal size or duration for a badger vaccination
programme. Benefits should start to accrue
from the onset of immunity and most badgers
(whether infected with TB or not) are expected to
die off within 5 years (Wilkinson et al., 2000).
A field trial was recently completed in Ireland
that should provide the first estimate of BCG effi-
cacy under field conditions. Lipid-encapsulated
BCG was delivered to the back of the throat of
anaesthetised badgers, while other badgers
received only the lipid as placebo. The study area
was divided into three equally representative
zones with different proportions (0%, 50% and
100%) of the badger population in each zone
being vaccinated with either BCG or placebo
(Gormley and Corner, 2013). A secondary
objective of the trial was to measure the effect of
BCG vaccine in badgers with pre-existing
M. bovis infection. When available, these data
will add to those from the relatively small field
study conducted in England with injectable BCG,
in which no evidence was found of either a
beneficial or detrimental effect of administering
vaccine to badgers already harbouring TB. In
addition to providing a measurement of protec-
tion and an estimate of vaccine efficacy, when
published, the field trial in Ireland will also pro-
vide a practical basis for assessing the logistics of
administering vaccine to wild badger popula-
tions annually on a large geographical scale.
14.5.3 Vaccination of wild boarThe wild boar is the main wildlife reservoir of
the M. tuberculosis complex (MTC) in Mediterra-
nean habitats of the Iberian Peninsula, where
TB prevalence in wild boar is associated with TB
occurrence on cattle farms (LaHue et al., 2016).
The wild boar is also involved in MTC mainte-
nance in many other regions (Gortázar et al.,
2015a). This native suid is widespread in Eurasia
and its populations are steadily growing despite
legal hunting (Massei et al., 2015). Wild boar are
highly susceptible to MTC infection and lesions
are most frequently found in the mandibular
lymph nodes, although over 50% of the cases
generalize, affecting the lungs and thoracic
lymph nodes (Martín-Hernando et al., 2007).
Recent evidence shows that inter-species con-
tacts involving wild boar are extremely rare in
Mediterranean habitats (Cowie et al., 2016), and
that transmission is most likely taking place
indirectly, for instance at shared waterholes
(Santos et al., 2015b; Barasona et al., 2016).
While attempts to control TB in wild boar or at
the wild boar–cattle interface through culling
and farm biosafety have yielded some progress,
vaccines will permit a more cost-effective and
sustainable disease control (Gortázar et al.,
2015b).
Both BCG and a heat-inactivated M. bovis
vaccine yielded significant protection (70–80%
lesion score reduction) in laboratory challenge
trials (Garrido et al., 2011; Beltrán-Beck et al.,
2014a; Gortázar et al., 2014). As mentioned
above for other wild hosts, the key attribute of a
successful TB vaccine would be to prevent the
spread of MTC infection to other wildlife or
domestic animals, with prevention of infection
being less relevant. The major challenges for
vaccinating wild boar are: (i) vaccine delivery
including the selective targeting of (mostly
uninfected) piglets while avoiding the risk of
accidental live-vaccine uptake by cattle and sub-
sequent positive TB-tests; (ii) vaccine safety for
target and non-target species; and (iii) vaccine
efficacy under field conditions. Regarding (i),
selective wild boar piglet feeders, a patented bait
and appropriate timing allowed delivery of oral
baits containing TB vaccines in a safe manner
(Beltrán-Beck et al., 2014b). Regarding (ii),
recent research has focused on heat-inactivated
M. bovis rather than on BCG. This implied full
safety, since neither vaccine strain survival in
host tissues nor vaccine strain transmission are
possible after proper inactivation (Beltrán-Beck
et al., 2014b). Finally, regarding (iii), two field
trials tested the efficacy of parenteral vaccina-
tion and of oral vaccination, respectively. In the
first one, 668 farmed wild boar piglets were par-
enterally (IM) vaccinated with heat-inactivated
M. bovis, while 182 were not vaccinated and
served as controls. In this low-prevalence
setting, parenteral vaccination protected
vaccinated individuals (66% reduction in
lesion prevalence) against natural challenge