232 P. Livingstone and N. Hancox
disease and preferred treatment of wildlife
( Bengis et al., 2002; Cassidy, 2012).
If wide-scale eradication of TB from cattle is
an extraordinary goal as espoused by Miller et al.
(2006), eradicating TB from a wildlife host as
well as from cattle is much more so. Neverthe-
less, with the right research knowledge and
detailed planning, costed strategic options
should be able to be developed for stakeholders
and the wider public to consider. This consider-
ation needs to involve technical and operational
validity, the concerns of affected parties and the
wider public, and a realistic assessment of costs
and benefits, which may fall much more widely
than for a programme involving cattle TB con-
trol alone. This will take time.
15.3.1 Determining the presence
of a tuberculosis in a wildlife
maintenance hostForemost in coming to grips with finding TB in
wildlife is proving which species is acting as a
maintenance host and whether it (or any other
species) is acting as a TB vector or source of
infection for cattle, as described by O’Brien et al.
(2011). In some cases, a complex multi-host epi-
demiological situation may become apparent,
which needs to be evaluated through detailed
epidemiological research and modelling. This
can be time-consuming and expensive. Figure
15.1 shows the level of interrelationships
identified for transmission of bovine TB in New
Zealand.
There are at least two alternative processes
that can be used to determine the presence of a
TB wildlife maintenance host. Firstly, the TB
maintenance host may emerge through the
accumulation of circumstantial evidence, anec-
dotal information and serendipitous findings
that point to the culprit species, with knowledge
gaps being filled in through later systematic
work as happened in New Zealand (Livingstone
et al., 2015a). Secondly, based on the New Zea-
land experience, the following describes a more
efficient process that could be used to identify the
presence of a TB maintenance host.
If a wildlife source of infection for cattle is
suspected but not proven, an epidemiological
review of all recent herd infections should be
undertaken. This should aim to identify any geo-
graphic clustering of recent herd infections that
are not clearly associated with livestock-only
infection pathways or sources (such as cattle
purchase or movement, mixing with infected
stock, or undiagnosed residual infection). Sig-
nificant clustering of herd infection that cannot
be explained by livestock pathways would ini-
tially suggest wildlife involvement. Further eval-
uation of this would require investigation of the
distribution and density of the suspected wildlife
species in proximity to clusters of infected herds.
Irrespective of the suspect species, post-
mortem surveys of the most common wildlife
scavengers in areas of concern will assist in
determining the extent of wildlife TB presence
(Byrom et al., 2015; Nugent et al., 2015b). As
identified by Byrom (2015) and Nugent (2015b),
scavenger species have relatively large home
ranges over which they will scavenge wildlife
carrion. If the carrion is from a TB-infected pop-
ulation, then over time the scavenger species will
also become infected. This can provide a rela-
tively quick way of determining the presence of
wildlife infection around clusters of herd infec-
tion, although survey design and species target-
ing needs to take account of factors such as
species longevity, population density, home
range and likely TB prevalence, for both the scav-
enger species and the suspected maintenance
host or hosts. (Byrom et al., 2015; Nugent et al.,
2015b).
If TB is identified in a wildlife scavenger spe-
cies, then further research will be required to
identify its epidemiological role as described by
Palmer (2013). It may turn out to be a mainte-
nance host as, for example, wild boar in Spain
(Boadella et al., 2012), or a spillover host such as
wild pigs in New Zealand (Nugent et al., 2015b).
If the infected scavenger species is deemed to be
a spillover host, then the exact source of infec-
tion will need to be determined for the scavenger
(i.e. which of its carrion source species was
infected). Information on the distribution and
home range attributes of the scavenger species
will help to define the geographic area in which
an intensified survey of other wildlife species
would be undertaken. Such a survey would sam-
ple intensively all wildlife species that are likely
to be carrion sources and are present in the
probable home range of the spillover TB animal.
If the likely maintenance host and vector for