Vaccination of Domestic and Wild Animals Against Tuberculosis 213
disease severity, while re-vaccinating deer at
intervals of 8- to 16-week intervals induced pro-
tection against infection, but not at an interval
of 43 weeks (Griffin et al., 2006). Parenteral BCG
administered to deer at a dose of 10^6 CFU and
oral BCG at 10^8 CFU induced a similar degree of
protection (Nol et al., 2008). Evidence has been
provided of transmission of BCG by shedding of
BCG from parenterally vaccinated deer to in-
contact, non-vaccinated deer (Palmer et al.,
2009, 2010; Nol et al., 2013). It is not known
whether these non-vaccinated deer would be
protected against TB. BCG was shown to persist
for 3 to 9 months in lymphoid tissues of deer
vaccinated parenterally or orally (Palmer et al.,
2010). Oral bait vaccines would be the most fea-
sible means to administer TB vaccines to large
populations of wild deer. However, a complica-
tion can relate to vaccine bait delivery where
there are bans in some TB-endemic areas (e.g.
Michigan, USA) on the supplementary feeding
of wild deer as a TB control measure to reduce
deer congregation in large numbers. Secondly,
there are concerns about non-target uptake of
vaccine baits, particularly by cattle.
Simulation modelling has examined the
potential role that vaccination could play in the
eradication of TB in wild deer in Michigan, USA,
and in control programmes to minimize cattle
herd breakdowns (Ramsey et al., 2014). Using a
vaccine with 90% efficacy, annual vaccination
of 90% of susceptible deer was necessary to
achieve a 95% probability of eradication within
30 years, whereas vaccination of 50–90% of
susceptible deer within a 5-km radius of cattle
farms could achieve a 95% probability of having
zero cattle herd breakdowns in 15–18 years.
14.5 Vaccination of WildlifeThe requirements of a TB vaccine for wildlife are
that the animals would only receive a single vac-
cination and, for practical purposes, the vaccine
would be self-administered via an oral bait. For
an oral bait vaccine to be left in the environ-
ment, the vaccine needs to be safe. These require-
ments can be met by using an attenuated
mycobacterial vaccine such as BCG and a sum-
mary of studies undertaken with BCG vaccine in
wildlife is shown in Table 14.2. The use of a
killed M. bovis vaccine for wild boar has also
shown promise.14.5.1 Vaccination of brushtail possumsThe brushtail possum is the major wildlife reser-
voir of M. bovis infection in New Zealand; it has
been declared a noxious pest. Possums are highly
susceptible to M. bovis infection and lesions are
found predominantly in the lungs and superfi-
cial lymph nodes. Culling of possums by trap-
ping and poisoning has been a major contributor
in the dramatic reduction in the numbers of
infected cattle over the past 20 years ( Livingstone
et al., 2015). Vaccination of possums against TB
has the potential to be an effective TB control
measure when it is not suitable to cull possums,
for example, near urban areas. The key attribute
of a successful wildlife TB vaccine would be to
prevent the spread of M. bovis infection to other
wildlife or domestic animals and prevention of
infection is of lesser importance compared to
that for domestic species. However, the major
challenges for the vaccination of wildlife are
vaccine delivery and need for a single dose vac-
cine. For the formulation of an oral bait BCG
vaccine, the BCG bacilli have been encapsulated
in a lipid matrix which protects the bacteria from
degradation in the acidic stomach environment
and enhances shelf life of the vaccine in the
field. This vaccine was shown to protect possums
against an experimental aerosol challenge with
M. bovis, (Aldwell et al., 2003). Vaccine-induced
immunity waned between 6 to 12 months post-
vaccination following oral vaccination and there
were no differences between BCG doses of 10^7
and 10^8 CFU or between Danish and Pasteur
strains of BCG (Buddle et al., 2006). A more
recent study indicated that protection against an
experimental M. bovis infection extended out to
28 months post-vaccination (Tompkins et al.,
2013). BCG bacilli were shown to be stable in the
lipid matrix for 7 weeks under room temperature
conditions and 3 to 5 weeks under field condi-
tions in a forest/pasture habitat, when main-
tained in weather-proof, bait-delivery sachets
(Cross et al., 2009). Uptake of oral bait placebo
vaccines was shown to be high, with 85 to 100%
of wild possums accessing baits at bait densities
of 40–80 sachets/hectare (Cross et al., 2009).