Bovine tuberculosis

Vaccination of Domestic and Wild Animals Against Tuberculosis 217

( Díez-Delgado et al., 2016). The second one
(2012–2016) tested the uptake rates and effi-
cacy of oral BCG and of oral heat-inactivated
M. bovis in high prevalence settings (40–80%
wild boar infection prevalence) in Montes de
Toledo, Spain. Results are still in preparation,
but preliminary analyses suggest that heat-
inactivated M. bovis performed better than BCG,
and that heat-inactivated M. bovis can signifi-
cantly contribute to TB control in wild boar
under field conditions (Díez-Delgado et al.,
unpublished data).
Ongoing laboratory research with heat-
inactivated M. bovis is also targeting other hosts
ranging from cattle, deer and goats (Roy et al.,
2017; Thomas et al., 2017; van der Heijden
et al., 2017). The multi-host nature and environ-
mental survival of MTC generates complexity, a
context where successful disease control strate-
gies will need to integrate all available tools,
including biosafety and prevention, population
control where possible, and vaccination.

14.5.3 Vaccination of ferrets

In New Zealand, ferrets (Mustela furo) can
become infected with M. bovis via feeding on
tuberculous carcasses, particularly possums,
and potentially can become a source of infection
for other wildlife or cattle (Byrom et al., 2015).
In most circumstances, ferrets are simply spill-
over hosts, but on rare occasions may act as
maintenance hosts when present in high densi-
ties. Vaccination has been considered as a possi-
ble control measure for ferrets and in the first of
two vaccination trials, ferrets orally vaccinated
with BCG incorporated into dietary meat were
partially protected against oral challenge with
virulent M. bovis (Qureshi et al., 1999). In the
second trial, vaccination of ferrets with BCG by
the subcutaneous route resulted in reduced
severity of disease following experimental infec-
tion with M. bovis (Cross et al., 2000). Ferrets
and badgers are members of the Mustelidae
family and because of availability and ease of
housing, ferrets may serve as a convenient
model for evaluating tuberculosis vaccines
designed for badgers. A new experimental infec-
tion model has been established in ferrets based
on aerosolised M. bovis (McCallan et al., 2011),

but reports assessing vaccine efficacy using this

model have yet to be published.

14.5.4 Vaccination of African buffalo

African buffaloes are the main wildlife reservoir

of M. bovis in some South African game parks,

and vaccination has been considered as one

of the few ethically acceptable control measures

that could be available. A vaccine trial was

undertaken to assess the efficacy of BCG vaccine

for buffaloes. Two doses of BCG were adminis-

tered subcutaneously and the buffalo were

challenged with virulent M. bovis via the intra-

tonsillar route. The study did not reveal signifi-

cant differences in the number of lesioned

animals between the vaccinated and control

groups (de Klerk et al., 2010). Delivery of a TB

vaccine to large herds of buffalo continually on

the move would be a considerable challenge.

14.6 Conclusions

Vaccination of cattle with BCG would have

greatest application in countries where test-and-

slaughter strategies are not affordable or socially

acceptable, and in this situation reducing the

spread of bovine tuberculosis would be very

valuable. However, vaccination would need to be

integrated with other control measures as vac-

cination alone is unlikely to induce complete

protection. It is well recognized in humans that

BCG confers some non-specific protective effects

against other pathogens (Garly et al., 2003).

This has yet to be evaluated in cattle, but could

potentially have benefits in developing coun-

tries. It is important that BCG is field tested in dif-

ferent environments and husbandry systems as

this may help explain any variations in vaccine

efficacy. Collaborations with human TB research

groups have resulted in the testing of a number

of the new human TB vaccines in cattle. No sin-

gle vaccine has been shown to be better than

BCG, although combinations of various subunit

TB vaccines and BCG have produced encourag-

ing results. There has been encouraging prog-

ress on the development of DIVA tests, and these

tests need to be evaluated in field situations and

their use shown to be cost-effective.